Davis’s Shieldback (Atlanticus davisi): COSEWIC assessment and status report 2020

Official title: COSEWIC assessment and status report on the Davis’s Shieldback Atlanticus davisi in Canada

Committee on the status of Endangered Wildlife in Canada (COSEWIC)
Threatened 2020

COSEWIC assessment summary

Assessment summary - November 2020

Common name: Davis’s Shieldback

Scientific name: Atlanticus davisi

Status: Threatened

Reason for designation: This flightless katydid is found only in six small areas of the sand barren and oak savannah habitats of the Norfolk Sand Plain in southwestern Ontario, where it occurs with other rare species of conservation concern such as Fern-leaved Yellow False Foxglove and Virginia Goat’s-rue. The Canadian population is estimated at fewer than 1500 mature individuals. The species has presumably declined over the past 150 years due to the over 90% reduction of dry oak woodland, savannah, and sand barren habitats in southern Ontario. This species depends on fire-maintained ecological communities, and the quality and quantity of this habitat have declined as a result of fire-suppression, forest succession, afforestation efforts, and invasive species. These threats continue with one site likely extirpated as a result of land clearing as recently as 2020.

Occurrence: Ontario

Status history: Designated Threatened in November 2020.

COSEWIC executive summary

Davis’s Shieldback
Atlanticus davisi

Wildlife species description and significance

Davis’s Shieldback (Atlanticus davisi) is a flightless member of family Tettigoniidae (katydids or bush crickets). Adults are 20-25 mm long with a mottled brown and grey colouration. As is typical of shieldback katydids, this species is robust, with a rounded head, a sculpted pronotum (shield-like plate) on the top and sides of the thorax, and a large bulging abdomen. Males have short leathery forewings that extend only a short distance beyond the pronotum and two short projections at the end of the abdomen (cerci). The wings on the female are entirely covered by the pronotum and a long sword-like ovipositor projects behind the abdomen. Nymphs are smaller and similar in appearance to adults except that the male forewings are not fully developed.

In Canada, Davis’s Shieldback occurs only in the southern Norfolk Sand Plain physiographic region in southern Ontario. These same habitats have additional species of conservation concern, such Fern-leaved Yellow False Foxglove and Virginia Goat’s-rue.

Distribution

Davis’s Shieldback occurs in eastern North America, with a range that extends from Iowa east to Vermont, southwards to North Carolina, and west to Arkansas. A disjunct population occurs in central Michigan. The distribution in Canada is restricted to a small area north of Lake Erie in southern Ontario. The Canadian population consists of six extant subpopulations, although the persistence of one subpopulation is uncertain.

Habitat

In Canada, Davis’s Shieldback is closely associated with oak woodland, oak savannah and sand barren habitats on dry sandy soils. It is most often found near forest edges, in woodland openings, or openings along forest access roads or trails. Key habitat features include the presence of well-drained sandy soils, dry leaf litter, low shrubs or saplings, and the availability of sunlight at ground level. Katydids tend to inhabit the leaf litter and above-ground shrubbery.

Biology

Davis’s Shieldback has one generation per year and grows through incomplete metamorphosis. It probably overwinters in the egg stage, with nymphs hatching in the spring, and undergoing a series of moults before maturing in early summer. Adults are active from July through September, perishing once temperatures drop below freezing.

The adults and nymphs eat plant and animal materials. Adults and nymphs are incompletely nocturnal, being most active from dusk until shortly after midnight, and only intermittently active during the day. Adult males produce songs (stridulations) by rubbing their wings; females do not sing. Their quiet but distinctive songs are useful in locating individuals and for species identification. The female uses her ovipositor to insert the eggs into the ground.

Population sizes and trends

The Davis’s Shieldback population in Canada is presumed to have declined; the extent of dry oak woodland, savannah and sand barren habitats in southern Ontario has declined by over 90% over the past 150 years. Habitat decline is continuing although the number of known subpopulations has increased due to increased search effort. Available data suggest the Canadian population is small, with a preliminary estimate of between 300-1310 mature individuals over the six extant subpopulations.

Threats and limiting factors

Threats to Davis’s Shieldback are primarily from ecosystem modifications driven by a combination of fire suppression, forest succession, afforestation and invasive non-native/native plant species. Habitat loss due to road construction, land clearing and light industrial development is ongoing at one of the six subpopulations (#1-6).

Davis’s Shieldback habitats are fire-dependent ecological communities. Fire suppression and the consequent invasion of woodland openings by native and non-native woody species are pervasive threats to the habitats of all subpopulations. These threats are partly mitigated by prescribed burning and other vegetation management activities at some protected areas.

A major historical cause of habitat loss in the Canadian range was the widespread planting of conifer plantations in dry sandy openings and open woodlands. Afforestation of open areas is a possible threat at Davis’s Shieldback sites outside protected areas.

Protection, status and ranks

Davis’s Shieldback and its habitat have no legal protection in Canada or Ontario. The six subpopulations are spread over 17 known landowners (referred to as sites): nine sites are in provincially owned protected areas, including Turkey Point Provincial Park and two separate tracts in the St. Williams Conservation Reserve. Three other sites are publicly owned lands that are not protected areas.

Davis’s Shieldback is critically imperilled in Canada (N1) and Ontario (S1). The species has not been ranked globally. In Michigan this species is imperilled or vulnerable (S2S3) and has been designated as a species of Special Concern. No other jurisdictions in the United States have assigned a conservation status to the species.

Technical summary

Scientific name: Atlanticus davisi

English name: Davis’s Shieldback

French name: Sauterelle de Davis

Range of occurrence in Canada: Ontario

Quantitative analysis

Is the probability of extinction in the wild at least [20% within 20 years or 5 generations, or 10% within 100 years]? Insufficient data

Threats (direct, from highest impact to least, IUCN threats calculator)

Was a threats calculator completed for this species? Yes. A threats conference call was held on 10 December 2019. The overall threat impact was rated as Low but adjusted to Medium-Low based on some unknown threats being probable. Known threats include:

1.2 Commercial and industrial areas (Low impact)

6.1 Recreational activities (Low impact)

7.3 Other ecosystem modifications (Low impact)

What additional limiting factors are relevant?

• Small disjunct geographic range
• Small individual territory and/or home range
• Low dispersal capability
• Northern limit of global range

Data sensitive species

Is this a data sensitive species No

Status History:

COSEWIC: Designated Threatened in November 2020

Status and reasons for designation:

Recommended Status: Threatened

B1ab(i,ii,iii,iv)+2ab(i,ii,iii,iv)

Reasons for designation:

This flightless katydid is found only in six small areas of the sand barren and oak savannah habitats of the Norfolk Sand Plain in southwestern Ontario, where it occurs with other rare species of conservation concern such as Fern-leaved Yellow False Foxglove and Virginia Goat’s-rue. The Canadian population is estimated at fewer than 1500 mature individuals. The species has presumably declined over the past 150 years due to the over 90% reduction of dry oak woodland, savannah, and sand barren habitats in southern Ontario. This species depends on fire-maintained ecological communities, and the quality and quantity of this habitat have declined as a result of fire-suppression, forest succession, afforestation efforts, and invasive species. These threats continue with one site likely extirpated as a result of land clearing as recently as 2020.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. Population trend is unknown.

Criterion B (Small Distribution Range and Decline or Fluctuation): Meets Threatened, B1ab(i,ii,iii,iv)+2ab(i,ii,iii,iv), because EOO is less than 20,000 km² (known EOO is 172 km²), IAO is less than 2000 km² (known IAO is 48 km²), (a) is known from fewer than 10 locations (estimate 8-11), (b) both the (i) extent of occurrence, (ii) index of area of occupancy are projected to decline based on development, (iii) an inferred and projected decline in the area, extent, and quality of habitat based on habitat loss and invasive species and (iv) number of locations or subpopulations is projected based on the development at one subpopulation.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable. Population trend is unknown.

Criterion D (Very Small or Restricted Population): Not applicable. Population, index area of occupancy, and number of locations is too large

Criterion E (Quantitative Analysis): Not applicable. Quantitative analysis not performed

COSEWIC history

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2020)

Wildlife Species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years

Extinct (X)

A wildlife species that no longer exists

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere

Endangered (E)

A wildlife species facing imminent extirpation or extinction

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed

Special Concern (SC)*

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats

Not at Risk (NAR)**

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances

Data Deficient (DD)***

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990

** Formerly described as “Not In Any Category”, or “No Designation Required.”

*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Wildlife species description and significance

Name and classification

Phylum: Arthropoda - arthropods

Class: Insecta - insects

Order: Orthoptera - grasshoppers, crickets and katydids

Family: Tettigoniidae - katydids, long-horned grasshoppers

Subfamily: Tettigoniinae - shieldback katydids

Genus: Atlanticus Scudder 1894

Subgenus: Atlanticus (Atlanticus) - eastern shieldback katydids

Species: Atlanticus davisi Rehn and Hebard 1916

Synonyms: Davis’s Shieldback (Rehn and Hebard 1916) is treated by some authors (e.g. Vickery and Kevan 1985) as a synonym of Least Shieldback (Atlanticus monticola Davis 1915). See discussion under taxonomic background.

French common name: Sauterelle de Davis

English common name: Davis’s Shieldback, Davis’s Shield-bearer (Cigliano et al. 2019), Davis’s Shieldback (e.g. iNaturalist)

Type locality: The holotype male, allotype female and paratypes of both sexes collected at Orange, Orange County, Virginia are housed in the Academy of Natural Sciences of Drexel University collection in Philadelphia, Pennsylvania (Rehn and Hebard 1916).

Taxonomic background and similarities: Thirty-one species in the genus Atlanticus are recognized by Cigliano et al. (2019), including 12 species in the subgenus Atlanticus which is restricted to eastern North America and 19 species in the subgenus Sinpacificus Bey-Bienko 1955 which is restricted to southeast Asia. North American Atlanticus species are referred to collectively as eastern shieldback katydids and their centre of distribution is the southeastern United States (Rehn and Hebard 1916).

Davis’s Shieldback (Atlanticus davisi) was first described in a comprehensive revision of the genus by Rehn and Hebard (1916), who considered it a “distinct and easily recognized type”. They split Least Shieldback (A. monticola Davis 1915) into two sibling species based on morphological differences and geographic range. They limited the geographic range of Least Shieldback to higher elevations in the southern Appalachians, whereas Davis’s Shieldback had a more extensive distribution (see Global Range).

Throughout this report, Mountain Shieldback refers to Atlanticus monticola Davis 1915 sensu stricto and Least Shieldback refers to A. monticola Davis 1915 sensu lato. The latter nomenclature is used when presenting information from sources that treat davisi as a synonym of monticola.

Rehn and Hebard (1916) acknowledged that Davis’s Shieldback and Mountain Shieldback may represent different forms of a single species occurring in different geographical and environmental situations but dismissed this possibility in the absence of any evidence of intergradation.

The status of Davis’s Shieldback as a full species was retained in the last revision of the genus (Rentz and Birchim 1968) and is accepted by Orthoptera Species Files (Cigliano et al. 2019) and the Integrated Taxonomic Information System database (ITIS 2019). Some widely used references (e.g. Vickery and Kevan 1985, National General Status Working Group 2017), field guides (e.g., Capinera et al. 2004; Elliott and Hershberger 2007) and websites (NatureServe 2019; SINA 2020) treat Davis’s Shieldback as a synonym, form or geographic population of Least Shieldback. For example, the Singing Insects of North America (SINA 2020) includes seven eastern shieldback katydid species. This difference in nomenclature results in some confusion regarding species identifications in parts of the United States.

Genetic information that could resolve the status of this species is not yet available. This species is represented by only 1 of 94 sequenced, bar-coded Atlanticus specimens in the Barcode of Life Database (BoldSystems 2020).

Any uncertainty as to whether Davis’s Shieldback is a full species or included within Least Shieldback does not affect this status assessment because the sibling species (Mountain Shieldback) does not occur in Canada.

Morphological description

Shieldback katydids develop through incomplete metamorphosis. After the eggs hatch, the juveniles (nymphs) grow through a series of instars before they become mature adults. Their annual life cycle is described further in Biology.

Adults:

Davis’s Shieldback adults (length 20-25 mm) have long antennae and large hind legs that are modified for jumping (Figure 1, 2). As is typical of eastern shieldback katydids, this species is robust, with a rounded head, sculpted shield-like plate (pronotum) on the top and sides of the thorax, and short leathery forewings (tegmina) that extend only a short distance down the large bulging abdomen. Adults and nymphs typically have a mottled brown and grey colouration, although a rare bright green colour morph has been reported from Virginia (Rehn and Hebard 1916). In adult males the exposed parts of the tegmina are about one-quarter the length of the pronotum and there are two short projections (cerci) at the end of the abdomen (Figure 1). In adult females the tegmina are entirely covered by the pronotum and a long sword-like ovipositor projects behind the abdomen (Figure 2).

Figure 1. Adult male Davis’s Shieldback (Atlanticus davisi) at Front Road site (#2b), Turkey Point Provincial Park on 14 August 2019 at 21:47. Photo by Mary E. Gartshore.

Figure 2. Adult female Davis’s Shieldback (Atlanticus davisi) (with spermatophore) at Burn Blocks site (#2d), Turkey Point Tract on 15 August 2019 at 00:39. Photo by Mary E. Gartshore.

Key features used to distinguish between Davis’s Shieldback and Protean Shieldback (A. testaceus), the only other eastern shieldback katydid known from Canada, are the relative length of the exposed tegmina in males, the relative length of the hind femur, and the shape of the subgenital plate and ovipositor in females (Rehn and Hebard 1916; Vickery and Kevan 1985). These morphological features are also useful in differentiating Davis’s Shieldback from the other eastern shieldback species that occur in eastern United States.

Juveniles (also called nymphs):

Nymphs are smaller but similar in appearance to adults except that the male tegmina are not fully developed (Figure 3).

Figure 3. Immature male Davis’s Shieldback (Atlanticus davisi), Manestar Field (#3a), Nursery Tract on 9 July 2019 at 13:48. Photo by Eric Giles.

Eggs:

The eggs have not been described.

Population spatial structure and variability

No information on population spatial structure or variability is available for this species. Considerable geographic variation in this species’ morphological features was observed by Rehn and Hebard (1916), who postulated that Davis’s Shieldback may be diverging into two forms.

Designatable units

Davis’s Shieldback is being assessed as one designatable unit in Canada. The Canadian population occurs entirely within a small area within the Great Lakes Plains National Ecological Area (COSEWIC 2015). There are no data on discreteness, genetic structure, or evolutionary significance among subpopulations.

Special significance

In Canada, Davis’s Shieldback is restricted to southern Ontario where it is closely associated with dry oak woodland, oak savannah and sand barren habitats. These habitats support many rare species that are of conservation concern in Canada such as Fern-leaved Yellow False Foxglove (Aureolaria pedicularia), Virginia Goat’s-rue (Tephrosia virginiana), Frosted Elfin (Callophrys irus) and Eastern Hognose Snake (Heterodon platirhinos). Within its Canadian range, this flightless insect may be an indicator of relict sand barren, oak savannah and oak woodland communities that are important refuges for a suite of remnant-dependent plant and insect species.

Distribution

Global range

The global range of Davis’s Shieldback is within eastern North America and extends from southern Ontario and northern Michigan east to Vermont, southwards to North Carolina, and west to Arkansas (Figure 4). Less than 1% of the global range is within Canada.

Figure 4. Global range of Davis’s Shieldback (Atlanticus davisi). Light grey shading indicates range of Davis’s Shieldback and red shading indicates approximate range of Mountain Shieldback, a sibling species which is restricted to higher elevations in the southern Appalachians. Black polygons indicate counties with records reported as Davis’s Shieldback (Bland 2003; BISON 2020a; GBIF 2020a; SCAN 2020a), Mountain Shieldback (BISON 2020b; GBIF 2020b; SCAN 2020b), or Least Shieldback (Walker 2016). Map by Alain Filion.

Because of differing nomenclatural treatments, the global range map (Figure 4) was generated using readily available vetted data for Davis’s Shieldback, Mountain Shieldback and Least Shieldback. These data include county-level records for Davis’s Shieldback in Michigan (Bland 2003), county-level records for Least Shieldback for North America (Walker 2016), and georeferenced specimen and observation records compiled in various online data portals (BISON 2020a,b; GBIF 2020a,b; SCAN 2020a,b).

The range of the Mountain Shieldback is confined to areas in the southern Appalachians region from 900-1800m above sea level (asl) from West Virginia to Georgia (extracted from Rehn and Hebard 1916; Rentz and Birchim 1968). Records of Least Shieldback from elsewhere in the eastern United States are inferred to be Davis’s Shieldback. The range of Mountain Shieldback does not extend within 400 km of any part of Canada (see Figure 4).

Canadian range

The range of Davis’s Shieldback in Canada is restricted to a small area north of Lake Erie in Norfolk County in southern Ontario (Figure 5). This range is confined to the southern part of the Norfolk Sand Plain physiographic region, a wedge-shaped zone of glacio-deltaic sand deposits (Chapman and Putnam 1984).

Figure 5. Davis’s Shieldback (Atlanticus davisi) distribution in Canada. Black circles indicate the sites where the species was confirmed present in 2019 or 2020. Half-filled circles indicate approximate positions of two previously known sites where presence was not confirmed during 2019-2020 search effort. Squares with X indicate other areas with potentially suitable habitat where this species was not detected during targeted searches in 2019-2020. See site number/letter codes in Table 2. Map by Alain Filion.

The Canadian range includes six subpopulations^{Footnote 1} (Table 1): #1 Simcoe West, #2 Turkey Point, #3 St. Williams Forest, #4 Nixon East, #5 Bill’s Corners West and #6 Pinegrove.

Notes on Table 1:

¹ Minimum convex polygon encompassing confirmed records for each subpopulation.

² Order of magnitude estimate of extent of potentially suitable habitat (openings and edges associated with dry oak forest, woodland, savannah, and sand barrens) within 2 km of known occurrences for each subpopulation.

³ Each land ownership/management parcel is considered a location (see Number of Locations).

⁴ Site includes multiple land parcels (see text).

Simcoe West (#1), Nixon East (#4), Bill’s Corners West (#5) and Pinegrove (#6) are each represented by a single known site^{Footnote 2}. Turkey Point (#2) and St. Williams Forest (#3) include multiple sites and multiple land ownership/management parcels (Table 1). All six subpopulations are considered extant, although the persistence of Simcoe West (#1) is uncertain due to the severe reduction in available habitat (see Habitat Trends and Threats).

Simcoe West (#1) and Nixon East (#4) are about 4 km apart, are spatially associated with the relict Delhi-Simcoe Prairies (Bakowsky and Riley 1992) and physically connected by the Simcoe-Delhi Rail Trail corridor. These subpopulations may have been contiguous in the past but are considered isolated as the two occupied sites are currently separated by more than 2 km of unsuitable habitat (i.e., agricultural cropland). Simcoe West (#1) and Bill’s Corners (#5) are about 3.5 km apart and are separated by unsuitable habitat.

The exact localities of the two unconfirmed sites (#3d and 3e) included in St. Williams Forest (#3) are uncertain but are < 4 km from the cluster of other sites (#3a, #3b, #3c) and the habitat is connected. The eight sites in Turkey Point (#2) are contiguous with strong habitat connectivity.

The record of Davis’s Shieldback from Shuswap Lake, British Columbia, included in the Global Biodiversity Information Facility (GBIF) database (GBIF 2020a) and other similar species information databases, is incorrect. The source of these records is specimens mis-labelled as “Atlanticus davisi (Teraguchi CLEV 1975)”. The identification of these specimens, from photographs, was determined to be Long-legged Anabrus (Anabrus longipes), a shieldback found in western North America (Miskelly pers. comm. 2019).

There is no evidence the Canadian range has changed since the species was first reported in Canada in 1939.

Extent of occurrence and area of occupancy

The extent of occurrence (EOO) using a minimum convex polygon around all known sites is 172 km². The index of area of occupancy (IAO) of the known sites is 48 km² (12 grid squares based on a 2 km x 2 km grid).

The EOO and IAO would likely increase with additional search effort. Targeted search effort in 2019 and 2020 led to an EOO increase of 37% (46 km²) and IAO increase of 33% (three grid squares). The EOO (including inferred habitat) is unlikely to be more than 250 km² (1.5 times known EOO) unless the species occurs outside its known range in Ontario (see Search Effort). Given the limited amount of suitable habitat within the known range and the species’ low dispersal capability, the IAO is estimated to be 60-80 km² (i.e. 3 to 8 additional grid squares).

The current status of Simcoe Junction Woods (#1a) is uncertain as much of the habitat where the species was found in 2019 has subsequently been destroyed. This site contributes 19% (32 km²) of the EOO and 8% of the IAO (1 grid square).

Search effort

Museum and sight records of Davis’s Shieldback in Canada date from 1939 to 2020 (Table 1). The species was first documented at Simcoe (#1) in 1939 and the most recent records are from multiple sites in 2020 (Table 1). Following accepted nomenclature (see Name and Classification), all Least Shieldback records from Canada are treated as Davis’s Shieldback (Paiero and Marshall 2014)(e.g., numerous museum specimens and older reports refer to Least Shieldback).

Few formal surveys that target katydids have been completed in southern Ontario. Canadian records of Davis’s Shieldback prior to 2001 appear to be the result of general insect collecting and incidental observations. In 2001, targeted surveys (by A. Timpf and D. Timpf) confirmed Davis’s Shieldback in the vicinity of St Williams Forest (#3). In preparation for this status report, targeted searches for Davis’s Shieldback were conducted in 2019 at the eight known sites, potential habitat within 1 km of the known sites, and other natural areas with potentially suitable habitat within Norfolk County (central part of Canadian range), Ontario (Table 1 and 2). Results of the 2019 surveys are summarized in Table 2.

Summary:

41 sites surveyed in 2019. One additional site surveyed in July 2020. Total of 14 confirmed sites. Two known sites not confirmed.

104.4 person-hours in 2019. 31.5 person-hours in 2020.

At least 96 males and 7 females detected at 14 sites in 2019. About 55 males and three females detected at two other sites in 2020.

¹ The Simcoe Junction Woods site extends multiple land parcels. Only the north section of this site was searched in 2019.

² The East Quarterline site includes a 2 km strip of roadside habitat that extends across several land ownership parcels.

³ Davis’s Shieldback was not historically recorded at these sites nor when searched in 2019-2020.

Search effort for katydids uses a combination of nocturnal acoustic and visual searches. Adult male katydids produce distinctive songs (i.e., stridulations) that are used for locating individuals and for species identification (Alexander et al. 1972). Recordings, audio spectrographs, and keys to aid in the identification of singing insects are available (e.g., Elliott and Hershberger 2007; SINA 2020). Davis’s Shieldback has a distinctive appearance and is easily captured or photographed. However, its mottled brown and grey colouration camouflages stationary individuals perched on dry leaves or bare sand. Adults are slow-moving and rarely observed during the day, even where they can be readily found at night. These factors make katydids somewhat challenging to survey.

The intermittent buzzy song of Davis’s Shieldback is relatively quiet, and the peak frequency of 15 kHz is near the limit of human hearing (Elliott and Hershberger 2007). Singing males are detectable at distances of up to about 20 m under ideal conditions (Heagy pers. obs. 2019). However, the soft song is easily overwhelmed by other noises, including other singing insects, rustling vegetation, running water, and anthropogenic noises. Where possible, searchers in 2019 followed trails and forest access roads to minimize noise interference. Meander searches through optimal habitats were also used to supplement the trail-based searches. Acoustic surveys in early to mid-July, before other insects are singing, are optimal (Gartshore pers. comm. 2019). Observers used a bright light to scan adjacent vegetation looking for perched katydids at heights of 0.5 m-1.5 m. At least one voucher photograph was taken at each site (Table 2).

A total of 41 sites were surveyed from July 14 - August 14, 2019 (Table 2). Surveys began at dusk and extended for four hours and totalled 104.4 person-hours. Effort per site ranged from 0.3 person-hours at a small site with little potential habitat, to 24.6 person-hours over several dates at larger habitats (e.g., 15 ha at #3a). The survey objective was to confirm presence at a site and search as many potential habitats as possible; once site occupancy was confirmed the search effort ended and additional suitable habitat was not checked. Davis’s Shieldback was confirmed at 14/41 sites.

An additional 33 person-hours of search effort was completed from July 14-18, 2020 including nocturnal searches at five sites where the species was not confirmed in 2019 and one site that was not surveyed in 2019 (labelled A - F, Figure 5; Table 2).

Unsuccessful methods included diurnal and crepuscular visual and acoustic searches; sweep netting low vegetation at dusk; nocturnal acoustic point counts; and use of a bat detector (Wildlife Acoustics Echometer Touch 2 Pro) to increase detectability. Incidental diurnal searches to find nymphs at two of the known sites (#2d and #3a) in June 2020 were not successful (Heagy pers. obs. 2020).

Davis’s Shieldback was not recorded during 10 person-hours of searches in reconstructed oak savannah habitat on former croplands at six sites, including areas adjacent to Nixon East Woods (#4a), within 1 km of St. Williams Forest (#3) and in the South Walsingham Forest natural area situated 6 km southwest of the St. Williams Forest (#3).

Search efforts in 2019 and 2020 were restricted to Norfolk County. Davis’s Shieldback has not been detected at other potential habitats in southwestern Ontario, including numerous sites at which past entomological search effort has been fairly intensive: Pinery Provincial Park (Skevington et al. 2001); Point Pelee National Park (University of Guelph 2009a); Rondeau Provincial Park (University of Guelph 2009b); and Ojibway Prairie Complex (Paiero et al. 2010). Other sites in southern Ontario with potential habitat (e.g. Camp Borden and Wasaga Beach in Simcoe County) have received limited search effort. No searches were conducted in prairie-savannah habitats on the Long Point peninsula as eastern shieldback katydids have not been reported from shoreline sand dune areas.

Analyses of the distribution of the Antenna-waving Wasp (Tachysphex pechumani) (Kurczewski 2000, 2008) may provide insight into the Canadian distribution of Davis’s Shieldback. Antenna-waving Wasp is associated with oak woodland and savannah vegetation and dry sandy soils in northeastern North America (Kurczewski 2000, 2008) and co-occurs with Davis’s Shieldback at some sites in Norfolk County.

The known distribution of Antenna-waving Wasp in Michigan, Indiana, Ohio, New Jersey and southern Ontario is correlated with counties with at least 5% well-drained sand soils (Kurczewski 2008). The distribution of Davis’s Shieldback in Michigan and Ontario appears to correlate strongly with counties with at least 25% well-drained sand soils as depicted by Kurczewski (2008). The disjunct distribution of Davis’s Shieldback in Michigan and Ontario (Figure 4) appears to be tied to the presence of excessive or well-drained sand. Norfolk County is the only county in southern Ontario with greater than 25% well-drained sand soils.

Davis’s Shieldback was captured in a malaise trap set on a private farm in Norfolk County in 2019. The trap was in or near a restored prairie. This represents a new subpopulation (#6 Pinegrove).

A female Davis’s Shieldback observed feeding on flying ants on a mothing sheet was likely attracted by the food source rather than by the black light (Israel pers. comm. 2019). Both malaise traps and light traps are not considered optimal methods for recording katydids.

There is no Aboriginal traditional knowledge available for search effort.

Habitat

Habitat requirements

In general, eastern shieldback katydids are surface-active shrub-inhabiting insects that are typically associated with dry upland woods, woodland edges and openings, dry brushy meadows, and damp meadows near wooded areas (Caudell 1907; Rehn and Hebard 1916; Blatchley 1920; Bland 2003; Elliott and Hershberger 2007).

In Canada, Davis’s Shieldback habitats are characterized by dry, coarse sandy soils, often with low dune ridges or knolls rising about the level sand plain surface. At these sites, the species is found in a limited range of upland vegetation types including oak woodland (Figure 6), oak savannah (Figure 7), and sand barrens and meadows with scattered trees and shrubs (Figure 8). Numerous Davis’s Shieldback observations are along forest edges, woodland openings, or openings along forest access roads and trails. Key habitat features include the presence of well-drained sandy soils, dry leaf litter, low shrubs or saplings, and ground level sunlight.

At a landscape scale, the Canadian sites are closely associated with remnant oak savannah and woodland habitats with some tallgrass prairie-savannah indicator plants (Bakowsky and Riley 1992; Rodger 1998; Tallgrass Ontario 2019). Davis’s Shieldback sites include canopy openings within relict woodlands (Figure 7), and disturbed habitats that are now in a semi-natural condition situated adjacent to oak or oak-pine woodlands or forests (Figure 8). Negative searches for this species in constructed oak savannah habitat suggests that the species is slow (or unable) to colonize newly available habitat patches, or that these constructed habitats are not suitable habitat.

Figure 6. Oak woodland habitat in the north woodlot at Simcoe Junction Woods (#1a). Pink flag indicates vegetation where male Davis’s Shieldback (Atlanticus davisi) was observed. Photo taken 25 August 2019 by Audrey Heagy.

Figure 7. Oak savannah habitat at Turkey Point Road Savannah site (#2a), Turkey Point Provincial Park. Habitat is being managed using infrequent prescribed burns. Photo taken 6 September 2019 by Audrey Heagy.

Figure 8. Manestar Field site (#3a). Interface of mixed oak-pine forest and cultural sand barren (sand dunes removed in 1970s). Davis’s Shieldback (Atlanticus davisi) adult males use scattered saplings and shrubs along this ecotone as nocturnal singing perches. Photo taken 22 August 2019 by Audrey Heagy.

In the eastern United States, Davis’s Shieldback are found in dead leaves and scattered undergrowth in deciduous woods in dry areas below ∼1000 m elevation (Rehn and Hebard 1916; Blatchley 1920; Vickery and Kevan 1985). In southern Indiana, the species is predominantly observed on high rocky, thinly wooded slopes (Blatchley 1920). In Michigan, Davis’s Shieldback has a disjunct range in the Northern Lower Peninsula Ecoregion (Cantrall 1968; Bland 2003), where it is associated with the Dry Northern Forests and Jack Pine (Pinus banksiana) Barrens habitat assemblage found on sandy outwash soils (Desrosiers et al. 2015). Habitats used in Michigan include dry, open deciduous woodlands, Jack Pine barrens and Leatherleaf (Chamaedaphne calyculata) bogs (Bland 2003). Within these habitats it is found on fallen leaves and low, mixed vegetation (Bland 2003). In central Michigan, Davis’s Shieldback and Protean Shieldback seem to use the same dry habitats, although only the latter species occurs in both northern and southern Michigan (Bland 2003). Recent observations from New York include nymphs found in a dry open sand pit with low shrubs including blueberry (Vaccinium sp.) and Sweetfern (Comptonia peregrina) mixed with bunchgrasses within an area of oak-pine forest, and an individual found along an open power line corridor on a hillside with blueberry and oak leaf litter (Woo pers. comm. 2020).

Habitat use may vary seasonally, as observed for Protean Shieldback, where in late summer adults opportunistically used diverse habitats in proximity to a dry woodlands edge and field opening, including orchard and marsh habitats (Gangwere 1966). Davis’s Shieldback’s use of Leatherleaf bogs in central Michigan may be opportunistic, as this atypical habitat is readily available in proximity to more typical dry semi-open habitats on well-drained sandy soils.

Habitat trends

The historical extent of tallgrass prairie, oak savannah and oak woodlands in southern Ontario, referred to collectively as tallgrass plant communities or tallgrass habitat, have ranged from 800 km² to more than 2000 km² (Bakowsky and Riley 1992; Rodger 1998; Tallgrass Ontario 2019). An updated analysis yielded an estimate of 1100 km² (Tallgrass Ontario 2019).

The extent of tallgrass plant communities remaining in southern Ontario is not fully understood and varies depending on the criteria used to define “intact” remnants. Estimates of the proportion of tallgrass habitat lost relative to what was documented during the 19^th century land survey includes 96% for southwestern Ontario (Bakowsky and Riley 1992) and 94% for southern Ontario (Tallgrass Ontario 2019). When the amount of habitat lost prior to European settlement or not recognized in the land survey is included, the total loss exceeds 99% (Bakowsky and Riley 1992). For the Norfolk Sand Plain physiographic region, which encompasses the known Canadian range of Davis’s Shieldback, the loss of tallgrass habitat has been extreme, with as little as 409 ha of intact tallgrass plant communities remaining compared to approximately 30,000 ha at the time of European settlement (Tallgrass Ontario 2019).

Although predominately an agricultural landscape, Norfolk County has a high amount of natural cover (approaching 25% of the land base) compared to other parts of southern Ontario (Figure 5). Vegetation in this region has been impacted by cultural activities for thousands of years. Prior to European settlement, Indigenous peoples used fire to promote and maintain an open woodland structure (Bakowsky and Riley 1992). Influences over the past two centuries include logging, land clearance, conifer afforestation, and fire suppression.

Given the correlation between the Davis’s Shieldback subpopulations and the prairie-savannah remnants in Norfolk County (as mapped by Bakowsky and Riley 1992 and Tallgrass Ontario 2019), habitat loss for this species in Canada over the past 150 years is > 90%, even after accounting for the species’ ability to persist in disturbed openings such as abandoned sand pits (#3c) and powerline corridors (#2c).

The amount of occupied and potentially suitable habitat for this species is limited. The extent of potentially suitable habitat at the 15 confirmed sites ranges from 2 ha (#1a, #2g) to 15 ha (#3a). The spatial extent of each subpopulation (based on the minimum convex polygon enclosing all confirmed sites) varies from less than a hectare each for two subpopulations (#1, #4) represented by a single site, to ∼200 ha for the eight sites in Turkey Point (#2) (Table 1). The total spatial extent of the occupied area (including unsuitable areas) at the six known subpopulations is approximately 250 ha.

The amount of potentially suitable habitat within 2 km of the known occurrences was estimated for each subpopulation by examining 2015 aerial photography overlaid with environmental mapping (e.g. contours, wetlands) (Norfolk County 2019a). Preliminary order-of-magnitude estimates of habitat availability suggest that < 10 ha of potentially suitable habitat is present near Simcoe West (#1), about 50 ha at the Bill’s Corners West (#5) and Pinegrove (#6), about 100 ha at Nixon East (#4), and approximately 1000 ha at each of Turkey Point (#2) and St. Williams Forest (#3) (Table 1). Total estimated potentially suitable habitat at the six subpopulations is approximately 2210 ha.

Habitat loss and degradation is ongoing, but the current magnitude of habitat loss is uncertain because of knowledge gaps regarding habitat use, microhabitat requirements, the rate at which habitat is being degraded due to invasive species and forest succession, and the extent to which habitat threats are being effectively mitigated by management activities (e.g. by prescribed burns, brush control) in protected areas . Comparison of aerial photography from 2015, 2006, and 1964 (Norfolk County 2019a) indicates that habitat quantity (e.g. extent of openings) has declined at most of the known sites.

Habitat loss is most apparent at the Simcoe Junction Woods (#1). The extent of remnant oak woodland at this site has decreased by more than 80% over the past 50 years and habitat loss continues. Between 2006 and 2015, the amount of woodland decreased from approximately 7.5 ha to 6 ha in three fragments due to new roads, land clearing and industrial development. Between 2015 and 2019, a 1 ha fragment was cleared. In 2020, all habitat at the Simcoe Junction North fragment was cleared (including area where species was confirmed occupied in 2019). As of July 2020, only 2 ha of wooded habitat remains (on adjacent fenced land parcel owned by Department of National Defence that has not been surveyed).

Efforts to maintain and restore degraded oak savannah habitat are ongoing in protected areas within Turkey Point (#2a, #2d) and St. Williams Forest (#3a, #3b, #3c). Over the past 10 years many tallgrass prairie-oak savannah habitats have been created on dry marginal agricultural lands in Norfolk County, including the planting and restoration of extensive areas near St. Williams Forest (#3) by the Nature Conservancy of Canada, and at Nixon East (#4a) under the Alternative Land Use Services (ALUS) program. To date, no instances of Davis’s Shieldback colonizing these reconstructed tallgrass habitats on former agricultural croplands have been documented. The constructed habitat is relatively new (planted 5 to 20 years ago) and targeted katydid search effort has been limited (∼25 person-hours in 2019).

Biology

There have been no studies on Davis’s Shieldback biology or natural history. Most of the information below is based on a four-year study of the similar Protean Shieldback in southern Michigan (Gangwere 1966, 1967) and the general biology of eastern shieldback katydids and other Tettigoniidae (Davis 1915; Rehn and Hebard 1916; Blatchley 1920; Rehn and Birchim 1968; Walker 1975; Vickery and Kevan 1985; Bland 2003). This published information is supplemented by field observations of Davis’s Shieldback in Canada.

Life cycle and reproduction

Davis’s Shieldback has an annual life cycle with one generation per year. The species grows through incomplete metamorphosis and probably overwinters in the egg stage, with nymphs hatching in spring, and undergoing a series of moults before maturing in late spring or early summer (Vickery and Kevan 1985). Eastern shieldback katydid adults and nymphs are omnivorous and incompletely nocturnal^{Footnote 3}.

Adult records for Canada range from July 3 - September 22. The date range for Davis’s Shieldback in Michigan is very similar (Bland 2003). Many males were heard singing after dusk (e.g., #3a) on 13 July 2019 (Boyd pers. comm. 2019; Israel pers. comm. 2019). The same observers noted singing males at this site on 3 July 2020 (Gartshore pers. comm. 2020). Singing at that site likely continued well into October that year, although the last observation was on 22 September (Heagy pers. obs. 2019). Females with spermatophores (sperm packages) were observed on 14 July 2019 and 14 August 2019 (Figure 2)(Heagy pers. obs. 2019).

The daily activity patterns of juvenile and adult Protean Shieldback were described as follows by Gangwere (1966, 1967). During the day, nymphs alternate between periods of activity when they briskly walk or jump over the ground, feed opportunistically, to periods of inactivity. Nymph activity peaks around dusk and continues until about 2 a.m. Adults are less active during the day, staying motionless or moving slowly. Adult activity increases towards dusk and is greatest from dusk to about 2 a.m. Males sing frequently at night and occasionally during the day. Nymphs and adults are completely inactive from early to late morning. Young nymphs are always on the ground in close association with dry leaf litter. During the day, adults may hide beneath leaves and debris, often at the base of shrubs or stout herbs. At dusk, late-stage nymphs and adults climb the vegetation and perch atop leaves, branches or stems. Males tend to use a limited number of plants whereas females move from plant to plant.

Nocturnal observations of adult Davis’s Shieldback in Canada fit these general behaviour patterns. Males have been observed perched on leaves, stems or twigs at heights of about 0.5 to 2 m and females perched horizontally on leaves or twigs approximately 0.2 to 0.5 m above ground level (Heagy pers. obs. 2019). Male Davis’s Shieldback were generally spaced out within the available habitat and only rarely on the same shrub, whereas two of seven females observed were on the same raspberry (Rubus sp.) plant (Heagy pers. obs. 2019).

Two observations of nymphs occurred during the day: nymphs were observed near the ground in spring pre-2002 (Gartshore pers. comm. 2019), and a late-instar male nymph moving on low vegetation and photographed on 9 July 2019 (Figure 3) (Giles pers. comm. 2019). Two eastern shieldback katydid specimens collected at Simcoe, Ontario on 19 June 1939 (Walley CNC 934466, 934467) are presumed to be nymphs of this species as an adult Davis’s Shieldback was collected at Simcoe, Ontario on 28 July of that year (Freeman CNC 934457). Diurnal observations of adults include a stridulating male on 1 September 1994 (Sutherland pers. comm. 2019), and a male photographed on low vegetation on 12 July 2010 (Gartshore pers. comm. 2019).

Adult Protean Shieldback numbers and singing activity peak within a few weeks of the onset of maturation and then decline gradually over the summer and early fall until the last survivors succumb to freezing temperatures (Gangwere 1966, 1967). Adult Grey Shieldback Katydid (A. dorsalis) held in captivity survived for up to 78 days after capture, although adult life expectancy in the wild is probably < 60 days (Walker 1975).

In general, females lay their eggs in the soil. The number of eggs per female is unknown. At a site in Michigan, Protean Shieldback preferentially oviposited in the woodland-open field ecotone, presumably as this habitat provided suitable microclimate for the development of the eggs and/or nymphs (Gangwere 1966). Eggs enter a state of diapause in temperate climates and, in many species, the egg stage persists for more than a year (Bland 2003). Availability of sunny areas with sparse vegetation, bare ground and dry leaf litter may be important for successful egg development and for the early nymph stages (Gangwere 1966).

Physiology and adaptability

Physiological information is not available for Davis’s Shieldback. Habitat specificity in Canada or elsewhere is not well understood but this species is able to utilize a range of open or semi-open vegetation types. In general, eastern shieldback katydids appear to be tolerant of habitat disturbance (e.g. found in abandoned sand pits, along power line corridors and access roads).

Dispersal and migration

Davis’s Shieldback is a flightless non-migratory species and unlikely to disperse more than a few hundred metres. A mark-recapture study of Protean Shieldback in southern Michigan found that, over a period of several weeks, adults moved an average of 37 m, with some sedentary individuals staying close to a home-base shrub and others moving about and covering distances of up to 168 m (Gangwere 1966). The same study found that habitat use and distribution within the study area changed over the annual life cycle. Young nymphs were closely localized along the ecotone between an oak-hickory woods and a dry abandoned pasture. Older nymphs and adults were dispersed through the field and woods as well as in the ecotone, and some were also present in an apple orchard and marsh adjacent to the field. Later in the summer, adults were commonest in the field, though some were calling within the woods, ecotone and orchard.

Specific information on the daily or lifetime movements of Davis’s Shieldback is not available. It seems likely that most individuals would move < 200 m and unlikely that an individual would move > 2000 m.

Interspecific interactions

In the United States, Davis’s Shieldback is known to co-occur with Protean Shieldback at sites in Virginia (Rehn and Hebard 1916), Indiana (Blatchley 1920), and central Michigan (Bland 2003); and with American Shieldback (A. americanus) at the type locality in Virginia (Rehn and Hebard 1916) and elsewhere in the eastern United States (Blatchley 1920). The global range of Protean Shieldback extends into extreme southwestern Ontario where it is known from a single site near Arner, about 200 km southwest of the Canadian range of Davis’s Shieldback (Marshall et al. 2004).

Shieldback katydids (subfamily Tettigoniinae) are also referred to as predaceous katydids as many are active predators of other insects, although most also scavenge dead insects and consume plant material (Capinera et al. 2004). Little is known about the specific food preferences of Davis’s Shieldback, but they are likely omnivores with a varied diet like other eastern shieldback katydids. The feeding behaviour of Protean Shieldback in Michigan differs seasonally and between males and females (Manley 1971): immature male and female diets consist of green plant material, adult males consume low-protein foods including dry oak leaves, and adult females are highly predatory on other insects. Prey generally consists of small, soft-bodied insects such as aphids, small caterpillars, lacewings and deerflies. Eastern shieldback katydids are not known to cause significant damage to vegetation or have significant impact on populations of other insect species.

Predators of eastern shieldback katydids include insectivorous birds and reptiles, spiders and other insects, including Great Golden-digger Wasp (Sphex ichneumoneus) (Davis 1915; Blatchley 1920; Bland 2003). The nymphs are particularly vulnerable to predators as they are more active throughout the day (Blatchley 1920). Features and behaviours common to all eastern shieldback species that may reduce predation risk include cryptic colouration, adults are primarily nocturnal, nymphs and adults are moderately strong jumpers, and all stages are flightless so not vulnerable to aerial predation by bats or birds. Information on pathogens and parasites is lacking.

Population sizes and trends

Sampling effort and methods

Survey methods are discussed under Search Effort. Past methods focused on confirming presence rather than estimating population size or trends.

Abundance

No abundance estimates are available for Davis’s Shieldback or other eastern shieldback species. In the United States, Davis’s Shieldback may be locally “not scarce” (Rehn and Hebard 1916) and other eastern shieldback species can be locally common, particularly as nymphs (Blatchley 1920; Gangwere 1966).

Within its Canadian range, Davis’s Shieldback appears to be local and rare. A minimum of 96 males and 7 females were detected at 12 sites during 104.4 person-hours of targeted nocturnal surveys in 2019 (Table 2). This total includes 54 males heard and/or seen during a 3.8 km nocturnal acoustic survey along trails through suitable habitat at (#3a) on 18 July 2019. About 55 males and a few females were detected at two additional sites (#2f, #5a) in 2020.

Preliminary estimates of the number of mature individuals in each subpopulation are based on the numbers of adults detected during the 2019-2020 targeted searches relative to the amount of potentially suitable habitat available (Table 2) and the extent of the search effort (approximately half of the potentially suitable habitat at each of the known subpopulations was searched). There is uncertainty associated with these estimates as detectability has not been quantified but is likely high under ideal conditions. Extrapolating from the results, the number of mature individuals in the known Canadian population could be 300-1310 individuals.

Fluctuations and trends

No information on subpopulation trends or fluctuations is available for Davis’s Shieldback or other eastern shieldback species in Canada or the United States.

In Canada, this species is inferred to have declined over the last century due to habitat loss and degradation, which continues to the present day (see Habitat Trends) although there is insufficient data to estimate a trend. Many sites are in protected areas where habitat is being actively managed to restore and maintain open woodland and savannah vegetation, but habitat loss and degradation is ongoing at other sites.

No documented Canadian subpopulation is known to be extirpated, although the current status of Simcoe West (#1) is uncertain as the habitat where the species was confirmed in 2019 was subsequently destroyed and very little potential habitat remains in the vicinity (see Habitat Trends).

Rescue effect

Rescue from other subpopulations both within Canada and from the United States is unlikely. The nearest known sites from Norfolk County and in the United States are south of Lake Erie in northeastern Ohio (100 km), central Michigan (300 km) and the Finger Lakes region of central New York (300 km). These distances are beyond the dispersal abilities of this flightless species. In addition to the physical barrier posed by the Great Lakes, most of the intervening terrestrial habitat is not suitable.

Threats and limiting factors

Known threats to Davis’s Shieldback primarily relate to habitat loss and degradation. Ecosystem changes due to the cumulative effects of fire suppression, natural forest succession, inappropriate afforestation, and the ingrowth of invasive non-native plant and forest pest species threaten the habitat of all subpopulations. Inappropriate recreational activities, specifically unauthorized all-terrain vehicle (ATV) use, is a threat at several sites. Industrial development is an imminent threat at one site.

Other threats were identified but considered historical (e.g. land clearing for agriculture, sand extraction), unlikely to occur within the next 10-year period (e.g. campground expansion), or to have minimal impact (e.g., specimen collecting, existing natural gas well and pipeline). However, the impact of other known, inferred or suspected threats (e.g. roads, forest pathogens, over-abundant herbivores, agricultural pesticides) remains unknown. Noise pollution is unlikely to impact this species as acoustic signalling (male-male and male-female) occurs over short distances and noise sources are restricted (e.g. traffic noise affects only a small part of the available habitat). This flightless species is not attracted to lights.

Threats to Davis’s Shieldback and its habitat are assessed using the International Union for Conservation of Nature-Conservation Measures Partnership (IUCN-CMP) threats calculator (Table 3) (see Salafsky et al. 2008; Master et al. 2012; Open Standards 2019). The overall IUCN-CMP threat impact is Medium-Low. The calculated impact of Low was adjusted due to the number of threats where the impact is unknown. Threats are discussed below in order of highest to lowest impact.

Table 3. Results for the Davis’s Shieldback threats assessment in Canada. The classification below is based on the IUCN-CMP (International Union for Conservation of Nature-Conservation Measures Partnership) unified threats classification system. For a detailed description of the threat classification system, see the CMP web site (CMP 2010). Threats may be observed, inferred, or projected to occur in the near term. Threats are characterized in terms of scope, severity, and timing. Threat impact is calculated from scope and severity. For information on how the values are assigned, see Master et al. (2009) and footnotes to this table.

Species Name: Davis’s Shieldback, Atlanticus davisi

Date of threats teleconference: 2019-12-19

Assessor(s): Audrey Heagy (report co-writer), Mary Gartshore (report co-writer), Dave Fraser (facilitator), Rosie Soares (COSEWIC Secretariat), Jenny Heron (Arthropods Co-chair and notetaker), Dave McCorquodale (Arthropods Co-chair), John Klymko, Jessica Linton, Rob Longair, Al Harris (Arthropod SSC members), Ken Tuininga (CWS), Colin Jones (Ontario representative and Arthropods SSC member), Gina Schalk (ECCC-Recovery planning, observer), Steve Paiero (external expert), Don Sutherland (external expert)

Assigned overall threat impact: CD = Medium-Low

Impact adjustment reasons: The overall threat was increased to medium-low as there are several “unknown” threats for this species. The low scores reflect what is known about actual threats, but the overall threat is likely higher

^a Threat numbers are provided for Level 1 threats (i.e., whole numbers) and Level 2 threats (i.e., numbers with decimals).

^b Impact-The degree to which a species is observed, inferred, or suspected to be directly or indirectly threatened in the area of interest. The impact of each threat is based on severity and scope rating and considers only present and future threats. Threat impact reflects a reduction of a specie’s population. The median rate of population reduction for each combination of scope and severity corresponds to the following classes of threat impact: Very High (75%), High (40%), Medium (15%), and Low (3%). Unknown: used when impact cannot be determined (e.g., if values for either scope or severity are unknown); Not Calculated: impact not calculated as threat is outside the assessment time (e.g., timing is insignificant/negligible [past threat] or low [possible threat in long term]); Negligible: when scope or severity is negligible; Not a Threat: when severity is scored as neutral or potential benefit.

^c Scope-Proportion of the species that can reasonably be expected to be affected by the threat within 10 years. Usually measured as a proportion of the species’ population in the area of interest. (Pervasive = 71-100%; Large = 31-70%; Restricted = 11-30%; Small = 1-10%; Negligible < 1%).

^d Severity-Within the scope, the level of damage to the species from the threat that can reasonably be expected to be affected by the threat within a 10-year or 3-generation timeframe. For this species a 10-year timeframe was used [OR] generation time of # years ([insert reference if available]) was used resulting in severity being scored over a #-year timeframe. Severity is usually measured as the degree of reduction of the species’ population. (Extreme = 71-100%; Serious = 31-70%; Moderate = 11-30%; Slight = 1-10%; Negligible < 1%; Neutral or Potential Benefit > 0%).

^e Timing-High = continuing; Moderate = only in the future (could happen in the short term [< 10 years or 3 generations]) or now suspended (could come back in the short term); Low = only in the future (could happen in the long term) or now suspended (could come back in the long term); Insignificant/Negligible = only in the past and unlikely to return, or no direct effect but limiting.

IUCN threat 7. Natural system modifications (low impact)

7.3 Other ecosystem modifications (low impact)

Several threats that result in ecological changes affecting the habitats used by Davis’s Shieldback are all included in this category including fire suppression (7.1), natural forest succession (8.2), inappropriate afforestation (2.2), and invasive non-native plant and forest pest species (8.1).

Suppression of wildfires (natural or anthropogenic) is ongoing at all sites. Fire suppression results in the degradation of open woodland, savannah and sand barren habitats as the growth of fire-sensitive woody plants leads to excessive shading and mesophication (shift from dry to mesic moisture regime).

In the absence of fire or active management, fire-sensitive native trees, particularly White Pine (Pinus strobus) and Red Maple (Acer rubra), invade sunny openings and/or create a dense understorey in open oak savannahs and woodlands. Over several decades, forest succession changes vegetation structure and composition to such an extent as to render the habitat unsuitable for Davis’s Shieldback.

Habitat availability and site connectivity in the two largest subpopulations, Turkey Point (#2) and St. Williams Forest (#3), continues to be impacted by the extensive planting of conifer trees in the 20^th century under a provincial reforestation program that targeted open sandy areas and resulted in the degradation of several ecologically significant savannah, prairie and sand barren areas across southern Ontario (Catling 2014). The threat of inappropriate afforestation has not been eliminated as current government incentive programs promote tree planting to sequester carbon and increase forest cover. Open sites on private or unprotected public lands could be lost if landowners decide to plant trees.

Invasive non-native plants are present to varying extents at all sites. Invasive non-native plants alter habitat in ways that can be detrimental to this species (e.g. this katydid prefers sparse ground vegetation not dense non-native cool-season grasses).

Oak Wilt Disease is caused by a fungus (Bretziella fagacearum) of unknown origin. This disease results in the rapid mortality of oaks, especially Black Oak (Quercus velutina). Oak Wilt Disease is expected to spread into southern Ontario within the next 10 years as it is present in Michigan close to the Canadian border. Mature and immature oaks are an important structural component of Davis’s Shieldback habitat. European Gypsy Moth (Lymantria dispar) is a cyclical non-native forest pest that has been established in Norfolk County for more than 40 years and causes increased (but not extreme) oak mortality. Both these non-native pests impact Davis’s Shieldback habitat quality and quantity.

The cumulative impact of these threats is considered low as the rate of ecosystem modification is relatively slow and is mitigated in part by vegetation management activities to restore and maintain open habitats (e.g., prescribed burning, brushing, plantation thinning, logging, invasive plant control and mowing) within protected areas and at some other sites. Small openings and canopy gaps at sites that are not actively managed will likely fill in completely over the next 10 years (Figure 9).

Figure 9. In-filling by early successional trees is reducing extent of open habitat at the Nixon East Woods site (#4a). Photo taken 14 September 2019 by Mary E. Gartshore.

IUCN threat 6. Human intrusions and disturbance (low impact)

6.1 Recreational activities (low impact)

Unmanaged recreational activities can have detrimental effects on this surface-active flightless insect and include direct mortality (e.g., trampling) and habitat degradation (e.g., soil disturbance, weeds). Frequent unauthorized motorized recreational vehicle use is ongoing in occupied habitat at two sites (#3a, #2h) and occasional ATV use is ongoing at several other sites (#2e, #2f, #2g, #3b, #3c, #5a). The impact of these activities is low as only parts of the sites are affected, the activity is typically during the day when katydids are not as active, and relatively few individuals would be directly harmed.

Authorized or informal recreational trails are present at most sites, although hiking, walking and use of the trails is considered to have a negligible impact on katydids. Managed recreational trails may be beneficial to this species if open canopy and edge habitat is maintained.

IUCN threat 1. Residential and commercial development (low impact)

1.2 Commercial and industrial areas (low impact)

Simcoe West (#1) is situated on the western edge of the town of Simcoe and is a small oak woodland within a municipal industrial park subdivided into small (2 ha - 5 ha) parcels that are zoned for general industrial developments. The area surrounding the woodland includes a mix of industrial uses and undeveloped lands (formerly agricultural fields). The woodland is located adjacent to a former railway junction and formal and informal recreational trails are present on the former railbeds. In 2019, the woodland consisted of two small parcels separated by a cleared right-of-way. The northern 2.5-ha wooded area, where a single individual was observed in 2019, was on a land parcel owned by Norfolk County at the time. The southern 2 ha wooded area is on an adjacent fenced land parcel owned by the Department of National Defence (DND). In 2020, the northern parcel was severed into two parcels, with one parcel sold for development and one parcel retained by the municipality to remain as a woodlot (Garwood pers. comm. 2020). However, as of May 2020 the entire northern wooded area had been cleared of all vegetation and topsoil.

It is possible that the species is present in the 2-ha wooded area on the southern parcel that has not been searched. Even if the remaining habitat is not directly impacted, ongoing industrial development in the surrounding area poses a threat to the persistence of this subpopulation.

Limiting factors

Limiting factors for Davis’s Shieldback are uncertain. The small disjunct Canadian population is at the northern limit of the species’ global range and all occurrences are restricted to one physiographic/ecological region. Climate, soil conditions, ground cover and vegetation are all factors that are likely to limit the occurrence of this species in Canada at various scales. The dispersal capability of this flightless insect is limited. The species does not have specialized food requirements and appears to be able to persist in relatively small patches of remnant habitat. The impact of localized events or management activities such as wildfires and prescribed burns can be magnified for insects with low dispersal capability occurring in small habitat patches in a highly fragmented landscape (Panzer 2002).

Number of locations

Known threats to Davis’s Shieldback are related to land use and habitat management. Each location^{Footnote 4} represents a specific land ownership/management arrangement, totalling 8-11 locations. The two tracts in the St. Williams Conservation Reserve (#2h, 3c) are separate locations because these tracts are approximately 10 km apart. The presence of the species at two locations (#3d and #3e) has not been confirmed since 2001. The persistence of the species at a third site (remaining habitat at site #1) is uncertain. Seven locations contain single sites and three locations (all protected areas) contain multiple sites (Table 1).

Protection, status and ranks

Legal protection and status

Davis’s Shieldback and its associated habitat have no legal protection in Canada or Ontario. The species is not covered by the Convention on International Trade in Endangered Species of Wildlife Fauna and Flora (CITES).

Non-legal status and ranks

The conservation status ranks for Davis’s Shieldback are listed below (NatureServe 2019). The NatureServe rankings apply to the broader taxon Least Shieldback, but only the narrower taxon Atlanticus davisi occurs in Canada.

• Global Status: SNR (species not ranked)
• Canada National status: N1 (critically imperiled)
• Ontario status: S1 (critically imperiled)
• United States National Status: SNR (species not ranked)
• United States subnational ranks: Michigan S2S3 (imperiled to vulnerable)

In Michigan, it is designated as a species of Special Concern, a non-legal status assigned to species that are rare and potentially imperiled (Bland 2003; MNFI 2019). Davis’s Shieldback is included as a Species of Greatest Conservation Need in the State Wildlife Action Plan for Michigan (Desrosier et al. 2005).

In the United States, Davis’s Shieldback is not protected under federal or state laws.

Habitat protection and ownership

Twelve sites are on publicly owned lands. Of these, nine sites are provincial Crown Land protected under the Ontario Provincial Parks and Conservation Reserve Act (#2a, #2b, #2c, #2d, #2e, #2f, #3a, #3b, #3c). The remaining habitat at the Simcoe Junction Woods site (#1) is part of the Frederick Hobson V.C. Armoury property managed by the Department of National Defence. The Fish Hatchery site (#2g) is on unregulated provincial Crown Land. The C5 Woods North site (#5a) is part of the C5 Community Forest owned and managed by Norfolk County.

The Gas Well Opening (#2h), Nixon Woods East (#4a) and Pinegrove (#6) sites are privately owned. Land ownership of the two unconfirmed sites (#3d and #3e) is unknown as there are several land parcels in the vicinity and the locality details of the roadside observations in 2001 are ambiguous (Timpf pers. comm. 2019).

Several private and public land holdings with potential habitat are present along the East Quarterline road near the general locality of the 2001 observation, including part of the western edge of the Nursery Tract (#3a) site. As no Davis’s Shieldback were found within the western part of the Nursery Tract in 2019, the historical observation is assumed to have been situated on a different land parcel and the East Quarterline site is considered a separate site (land ownership unknown).

Little suitable habitat is present adjacent to the 4^th Concession Road, an unmaintained sand road thorough Backus Woods, which is the purported locality for the historical observation referred to as the Backus Dry Edge site. Most of the proximal lands are part of the Backus Block of lands owned by the Nature Conservancy of Canada and managed for conservation purposes. However, there are some private land holdings immediately adjacent to the reported locale.

Treed areas at all sites are identified as Significant Woodlands under the Norfolk County Official Plan (Norfolk County 2019b) and have some protection against development or site alteration under section 2.1.5.b of the Provincial Policy Statement, 2014 (MMAH 2014), as well as under the municipal tree-cutting bylaw^{Footnote 5} (Norfolk County 2006). Open habitats at these sites do not have protection.

Authorities contacted

Bland, Roger. G. Biologist (retired), Central Michigan University, Mount Pleasant, Michigan.

Catling, Paul. Research Scientist, Agriculture and Agri-food Canada, Ottawa, Ontario.

Jones, Colin. Provincial Arthropod Zoologist, Natural Heritage Information Centre, Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario.

Lonsdale, Owen. Collections Manager Canadian Museum of Insects, Arachnids and Nematodes, Ottawa, Ontario.

Miskelly, James. Research Associate in Entomology, Royal BC Museum, Saanich, British Columbia.

Packer, Laurence. Department of Biology, York University, Toronto, Ontario.

Paiero, Steven, Curator, University of Guelph Insect Collection, Guelph, Ontario.

Sutherland, Don. Zoologist, Natural Heritage Information Centre, Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario.

Timpf, Adam. Biologist, Walsingham, Ontario.

Woo, Brandon. Orthoptera expert and undergraduate student, Department of Entomology, Cornell University, Ithaca, New York.

Acknowledgements

Many people greatly assisted the authors by generously sharing their knowledge of the occurrence of this species in Ontario, tracking down previous records, providing the necessary landowner permissions, or by assisting with the search effort. Adam Timpf provided valuable information on his previous survey efforts and the sharp ears and eyes of Alex Israel and Brendan Boyd made a very significant contribution to the success of the field surveys in 2019. Thank you to the private and public landowners who provided permission to access their properties.

Thanks to Jennifer Heron (Arthropod SSC Co-chair), Rosie Nobre Soares and Marie-France Noel (COSEWIC Secretariat) for contract supervision and advice. Alain Filion (COSEWIC Secretariat) produced the range maps. Review comments and suggestions were provided by the Arthropod Specialist Subcommittee, COSEWIC members and jurisdictional reviewers: Bob Anderson, Marie Archambault, Syd Cannings, Kristen Diemer, Allan Harris, Colin Jones, John Klymko, Dan Kraus, Rob Longair, David McCorquodale, Jeffrey Ogden, Leah Ramsay, James Miskelly, Remi Hubert, John Richardson, Cory Sheffield, Donald A. Sutherland, Jessica Linton, Sarah Semmler, Brian Starzomski, Jeremy deWaard, Michel Saint-Germain and Ken Tuininga.

The status report writers would like to thank everyone who contributed to this report by providing expert advice, unpublished information, checking insect collections, or by participating in the threat assessment. Their names are cited elsewhere in this report.

Front cover photograph by Mary E. Gartshore.

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Biographical summary of report writer(s)

Audrey Heagy is a field biologist, technical writer and conservation practitioner with over 30 years’ experience working for non-profit conservation organizations and as an independent consultant, primarily in southern Ontario. Lead technical writer for five COSEWIC status reports (4 bird species, 3 plant species), the Ontario Barn Swallow Recovery Strategy (2014), and many other technical reports and documents. Extensive experience in planning, implementing and reporting on biological surveys and habitat management for species at risk in southwestern Ontario, particularly at the St. Williams Conservation Reserve.

Mary E. Gartshore has over 40 years’ experience as a field biologist, conservation biologist and ecological restoration practitioner in Ontario, Africa and elsewhere. She has extensive experience in all aspects of native plant production for ecological restoration projects in Ontario as principal of Pterophylla native plant nursery and the St. Williams Nursery and Ecology Centre. She has carried out extensive fieldwork in southwestern Ontario including the Haldimand-Norfolk Natural Areas Inventory 1986-1987, the Southern Ontario Woodlands Biodiversity Study 1994-1995, and St. Williams Crown Forest Life Science Inventory 2001.

Collections examined

The following collections were checked for specimens of Davis’s Shieldback or any other Atlanticus species collected in Canada:

• CNC: Canadian National Collection of Insects, Arachnids and Nematodes, Ottawa, ON (Owen Lonsdale)
• CLEV: Cleveland Museum of Natural History (Nicole Gunter)
• DEBU: University of Guelph Insect Collection, Guelph, ON (Steve Paiero, GBIF 2019)
• GLFC: Great Lakes Forestry Centre, Sault Ste. Marie, ON (Kevin Barber)
• LEMQ: Lyman Entomological Museum, McGill University, Ste. Anne de Bellevue, QC (Stéphanie Boucher)
• ROME: Royal Ontario Museum, Toronto, ON (Brad Hubley)