Western chorus frog: science assessment
Table of Contents
- 1. An Overview of the Western Chorus Frog
- 1.1. Species Status
- 1.2. Biology
- 1.3. Distribution
- 1.4. Threats
- 1.5. Habitat and Population Status and Trends
- 1.6. Capability to Create Western Chorus Frog Habitat and a New Metapopulation
- Appendix A - Figures
- Appendix B - Tables
List of Figures
- Figure 1. Western Chorus Frog faunal provinces and observations of the species in the Carolinian and the Great Lakes / St. Lawrence faunal provinces (adapted from COSEWIC 2008). Observations above the grey shared area fall in the Canadian Shield faunal province.
- Figure 2. Historical and current ranges of the Western Chorus Frog (GLSLCS) in the Outaouais and Montérégie regions of Quebec (modified from unpubl. MFFP 2015).
- Figure 3. Areas of remaining and destroyed suitable habitat for Western Chorus Frog between 1991 and 2014 in five regions of Outaouais.
- Figure 4. Areas of remaining and destroyed suitable habitat for Western Chorus Frog between 1992 and 2013 in metapopulations and populations of northeastern Montérégie.
- Figure 5. Areas of remaining and destroyed suitable habitat for Western Chorus Frog between 1992 and 2013 in metapopulations and populations of southwestern Montérégie.
- Figure 6. La Prairie Western Chorus Frog metapopulation. Areas of residual and destroyed suitable habitat for Western Chorus Frog including the destruction of habitat caused by de development of Phases 1, 2 and 3 of the Symbiocité residential project. Active, destroyed, isolated and threatened Western Chorus Frog breeding ponds.
- Figure 7. Destruction of known Western Chorus Frog breeding ponds in La Prairie from 1999 until 2014.
- Figure 8. Distribution of Western Chorus Frog GLSLCS habitat units.
List of Tables
- Table 1. Comparison of the area of suitable habitat for Western Chorus Frog between 1991 and 2014 in five regions of Outaouais.
- Table 2. Comparison of the area of suitable habitat for Western Chorus Frog between 1992 and 2012 in metapopulations and populations of Montérégie.
- Table 3. Status of the nine Western Chorus Frog metatpopulation in Montérégie between 2004 and 2014 including number of active and destroyed breeding ponds (modified from Picard 2015).
- Table 4. Marsh Monitoring Program (MMP) trends in the mean probability of occurrence for the Western Chorus Frog in Ontario from 1995-2014.
- Table 5. Known or proposed projects that intersect (within 300 m) or are nearby (within 1 km) of a Western Chorus Frog (WCF) occurrence or that occur within a census division containing the species.
List of Appendices
- Appendix A - Figures
- Figure A. 2011 Ontario census divisions (Statistics Canada 2012). A total of 49 census divisions occur in Ontario, 39 of which contain observations of the Western Chorus Frog (GLSLCS).
- Figure B. Southern Ontario study area for wetland loss (figure taken from Ducks Unlimited Canada 2010).
- Figure C. Area where agriculture occurs within Ontario, Canada (boundary between northern and southern Ontario shown) (figure taken from Smith 2015).
- Appendix B - Tables
- Table A. Habitat units created from 300m buffers around observations. Critical habitat units identified in the federal recovery strategy are also presented for comparison.
- Table B. SOLRIS land cover change. Census divisions are listed in order of potential habitat loss.
- Table C. Wetland loss since pre-settlement. Counties are listed in order of greatest trend in % wetland loss 1982-2002 (Ducks Unlimited Canada 2010).
- Table D. Projected population growth from 2013 levels for census divisions containing the Western Chorus Frog (GLSLCS) in Ontario.
1. An Overview of the Western Chorus Frog
This scientific assessment provides an up to date Western Chorus Frog population status in Canada as well the status and trends of Western Chorus Frog habitat. The information considered in this assessment includes information provided by the provinces of Quebec and Ontario, various municipalities, conservation authorities, non-governmental organizations, species experts, federal departments and Quintcap Inc. (the developer of a residential project in La Prairie, Quebec), in addition to scientific literature and reports. It builds on information presented by COSEWIC (2008) and the Recovery Strategy for the Western Chorus Frog (Pseudacris triseriata), Great Lakes/St. Lawrence – Canadian Shield population, in Canada (Environment Canada [In press], hereafter referred to as the federal recovery strategy).
This assessment shows habitat loss and a decrease in site occupancy Content Footnote1 for Western Chorus Frog in both Quebec and Ontario. Mean probability of occurrence has decreased 2.6% per year in Ontario from 1995-2014 (equivalent to a 26% cumulative loss over the 10-year period) (Tozer pers. comm. 2015). Assuming the assessment is indicative of a true population trend, should the rate of decline continue it may be a cause for concern. Habitat analysis also shows a slight decrease of 0.42% in Western Chorus Frog suitable habitat in the Great Lake and St. Lawrence faunal province (Figure 1). In Quebec, where nine metapopulations existed in the Montérégie area in 2004, six are believed to still be extent (Picard 2015). Still in Quebec, habitat trends show a decrease in suitable Western Chorus Frog habitat of 7.4% between 1991-2014 in Outaouais region and 23.6% in Montérégie region between 1992-2013, with the greatest loss at the La Prairie Western Chorus Frog metapopulation (within the Montérégie region) where 57.3% of Western Chorus Frog suitable habitat was lost between 1992-2013. Should further development occur at that site, the amount of suitable habitat for Western Chorus Frog as well as connectivity between breeding ponds would further diminish. Continued loss of suitable habitat and connectivity reduces the likelihood of long-term viability of this metapopulation and reduces its potential for recovery.
1.1. Species Status
Two designable units (DUs) of Western Chorus Frog in Canada were determined by COSEWIC (2008, 2010), namely the Carolinian population and the Great Lakes/St. Lawrence – Canadian Shield (GLSLCS) population. The geographic boundary dividing the two DUs corresponds to the boundary between the Carolinian and Great Lakes/St. Lawrence faunal provinces (Figure 1). The Western Chorus Frog GLSLCS population was listed as Threatened under Schedule 1 of the Species at Risk Act (SARA) (S.C. 2002, c. 29) in 2010, while the Carolinian population was designated as Not at Risk. From a taxonomic perspective, a review of available scientific literature indicates that the Great Lakes/St. Lawrence – Canadian Shield population of chorus frogs is referenced by one of two taxonomic names: Western Chorus Frog (Pseudacris triseriata) or Boreal Chorus Frog (Pseudacris maculata). New information available since the 2008 status assessment of the GLSLCS population of Western Chorus Frogs prepared by COSEWIC suggests that the population belongs to the Boreal Chorus Frog species.
All available information was considered, including that received from COSEWIC and the developer (affidavits by Hamel 2015 and Lapointe 2015), as well as the published studies from Moriarty-Lemmon and colleagues (2007) and Rogic and colleagues (2015). Of all of those sources of information, greatest weight was placed on a clarification provided by COSEWIC, rather than on the conclusions of independent authors. COSEWIC is the authoritative body in Canada established as an independent arm's length technical committee responsible for determining the wildlife species, subspecies or other biological 'unit' that is to be assessed, and for conducting a status assessment of that biological 'unit'. COSEWIC brings together species specialists from across the different classes of animals and plants, and, on the basis of that collective expertise and knowledge, determines the taxonomic classification of each biological 'unit' it assesses.
The clarification provided by three representatives of COSEWIC took into account all of the new technical information, including the technical information that the developer had cited, since COSEWIC's assessment of the Western Chorus Frog (GLSLCS) that was completed in 2008. Rather than finding the new technical information to be conclusive, the COSEWIC clarification confirms there is continued uncertainty. In light of this continued uncertainty, this assessment relies on the pre-existing assessment of COSEWIC given their expertise in this matter and because this also ensures continued protection for the species under SARA. As a result and for the purposes of this assessment, the term Western Chorus Frog used hereafter refers to the individuals in southern Ontario and Quebec falling in the Great Lakes/St. Lawrence and Canadian Shield faunal provinces.
In Quebec, the Western Chorus Frog GLSLCS population has been listed as Vulnerable under the provincial Act Respecting Threatened or Vulnerable Species (R.S.Q., c. E-12.01) since 2001, and its status is currently under review. In Ontario, the debate among experts over the genetic classification of the Western Chorus Frog and the Boreal Chorus Frog in Ontario led the committee on the Status of Species at Risk in Ontario (COSSARO) to treat Western Chorus Frog as a single population in Ontario, and classified it as not at risk under the Ontario Endangered Species Act, 2007 (S.O. 2007, c. 6) (COSSARO 2009).
The WCF is a small amphibian, about 2.5 cm in length, which usually breeds in temporary wetlands devoid of predators, such as fish and larger anurans, and located near open habitats or discontinuous forests. The life expectancy of adult Western Chorus Frog is usually one year (a single reproductive event), although some have been known to live up to two or three years (Whiting 2004).
The habitat needs of the Western Chorus Frog are presented in the federal recovery strategy for the species. The species requires habitat within its home range for breeding, foraging, movements, and hibernation and also requires habitat outside of its home range for dispersal. Western Chorus Frog populations can be connected by processes of migration, genetic exchange and colonization, forming larger units called metapopulations. A metapopulation structure is highly dependent on connectivity and, where it occurs, is a key element to maintaining genetic diversity and to providing resilience from natural or anthropogenic disturbances. Western Chorus Frog metapopualtion structures have not yet been determined in Ontario, hence, an assessment at the metapopulation level was only conducted for Quebec.
The distribution of the Western Chorus Frog extends from the east-central United States to southwestern Quebec. In Canada, the Western Chorus Frog is found in the lowlands of south-central and eastern Ontario as well as south-western Quebec.
In Quebec, the Western Chorus Frog was historically present in the southern part of the province, from the Ottawa Valley to the foothills of the Appalachians and west of the Richelieu River (Bonin and Galois 1996; Picard and Desroches 2004; Figure 2). Currently, the species is estimated to occupy 10% of its former range (Bonin and Galois 1996).
In Ontario, the Western Chorus Frog is more widespread with a range that extends from the United States border (in the east) and Carolinian- Great Lakes/ St. Lawrence faunal province boundary (in the west) northward into the southern part of the Canadian Shield faunal province. It extends eastward from the Sault Ste. Marie area to the Ottawa Valley and along the St. Lawrence River into the province of Quebec. It should be noted that a small number of records of Western Chorus Frog fall within the districts of Cochrane and Timiskaming. These records were retained for this assessment because a northern boundary for the DU was not defined by COSEWIC, and the records occur east of the range of the Boreal Chorus Frog.
As described in the federal recovery strategy, the primary threats to Western Chorus Frog are habitat loss and degradation through urban development, intensification of agriculture, climate change, pesticides and fertilizers, the expansion and maintenance of linear infrastructures, as well as habitat succession. Additional information has been gathered pertaining to these threats and is presented in section 1.5, Habitat and Population Status and Trends.
In addition to the threats identified in the federal recovery strategy, this assessment found evidence of additional potential threats to the species, including: hydrological changes caused by American Beaver (Castor canadensis), a species native to the GLSLCS region, and habitat alteration by an invasive species, European Buckthorn (Rhamnus cathartica) (Sacerdote and King 2014).
1.4.1. Hydrological Changes Caused by American Beaver
Landscape conversion and changes in hydrology due to American Beaver is a threat to the habitat of the Western Chorus Frog. Beaver dams can result in changes to hydrology and loss of habitat required by the species for breeding, foraging and dispersal. When ephemeral wetlands used by Western Chorus Frog are converted to beaver ponds, predation and competition are increased. Dams created by the American Beaver can also limit the flow of water to downstream wetlands used by the Western Chorus Frog, making them unsuitable for Western Chorus Frog breeding. In addition, American Beaver clearings can change microclimate of wetlands, having similar impacts to that of anthropogenic landscape conversion or climate change (Skelly and Freidenburg 2000).
In Quebec, this threat has been identified since at least since 2010 (Tommy Montpetit, pers. comm. in Picard 2015). When looking at the causes of breeding pond destruction between 2004 and 2014 in the Montérégie region, flooding caused by American Beaver came second to residential development (Picard 2015). For example, in the Bois de Brossard–Sud and Boisé-du-Tremblay metapopulations, Picard (2015) identified that beaver dams were responsible for a major decline in the number of active breeding ponds. The impact of American Beaver induced landscape conversion on Western Chorus Frog is unknown in Ontario; however, there is potential for habitat loss in areas where ephemeral wetlands become permanently lost and are not replaced. In the Ottawa area, where American Beaver recolonized in the 1950s and populations peaked around the late 1990s, significant amounts of swamp have been converted to marsh, and wetlands have expanded in some areas of low relief since the 1950s (Stow pers. comm. 2015). Hill and Duval (2009) found that Beaver dams in southern Ontario raised the riparian water table up to 1m and resulted in significant changes to subsurface hydrology and chemistry.
Some studies have shown that landscape change driven by the American Beaver can be beneficial for amphibians. Beaver ponds can provide suitable habitat for several amphibian species (Cunningham et al. 2007, Stevens et al. 2007) and beaver canals can function as movement corridors (Anderson et al. 2015) and increase the rate of wetland colonization (Hossack et al. 2015). Over time, Beavers create a diverse landscape of both active and abandoned ponds which are suitable to different species with different habitat needs (i.e., various hydroperiods and presence or absence of fish) (Cunningham et al. 2007). However, where surrounding natural environments are destroyed or altered by human activities, it is possible that the modification of residual habitat by the American Beaver makes it temporarily unsuitable for the Western Chorus Frog. In this case, the individuals would be unable to seek refuge in peripheral sheltered habitat, leading to the extinction of the local population. If the peripheral sheltered habitat is too remote, it is also unlikely that Western Chorus Frog would be able to quickly recolonize large American Beaver pond complexes once the beavers have left (Picard 2015).
1.4.2. Invasive Species - European Buckthorn
Invasive European Buckthorn poses a potential threat to the Western Chorus Frog in Ontario and Quebec. A study conducted in northeastern Illinois (Sacerdote and King 2014) examined leaching of the compound emodin from European Buckthorn leaves in two ephemeral breeding pools that contained breeding Western Chorus Frog. Based on embryos collected from the breeding pools it was concluded that the severity of embryo malformations increased with rising emodin concentrations (Sacerdote and King 2014). The increase in embryo mortality and malformation resulting from emodin may limit recruitment; thus, the compound has been linked to regional declines in amphibian populations including the Western Chorus Frog (Sacerdote and King 2014). The compound becomes a concern when it is released into breeding ponds in high concentrations which is observed when dense dominant stands of emodin producing plants occur (Sacerdote and King 2014). In Ontario, the invasive European Buckthorn grows in dense monospecific stands within suitable habitat for the Western Chorus Frog. In some areas the removal of European Buckthorn has resulted in increased growth of Glossy Buckthorn (Frangula alnus), another invasive emodin producing plant (Anderson 2012).
The geographic range of invasive European Buckthorn overlaps with range of the Western Chorus Frog in Ontario and in Quebec, and may result in the degradation of suitable habitat and direct mortality. European Buckthorn is widespread in Canada from Saskatchewan to Nova Scotia. The species is common in southern Ontario but rare north of the Canadian Shield (Anderson 2012). European Buckthorn and Glossy Buckthorn are considered the most aggressive invasive species in wetlands in the Ottawa area (Anderson 2012). European Buckthorn has also been identified as a threat to the Western Chorus Frog in London, Ontario where both Western Chorus Frog and high densities of invasive European Buckthorn occur (McDougall pers. comm. 2015). European Buckthorn is also currently considered a threat in at least two Western Chorus Frog metapopulations in Quebec, namely Boisé-du-Tremblay and Bois de Brossard, where it invades Western Chorus Frog habitat.
The potential for emodin to contribute to localized and regional amphibian decline poses a threat to population persistence for Western Chorus Frog in Ontario and Quebec, although the severity and extent of the impact is unknown. Best management practices have been developed for controlling invasive European Buckthorn (Anderson 2012). The control of this invasive species will help to maintain conditions that benefit amphibians including native plant diversity, habitat structure, and soil moisture regimes (Klionsky et al. 2010).
1.5. Habitat and Population Status and Trends
A population trend analysis looks at variation in population size, spatial distribution and density. When demographic data (number of mature individuals, fertility, mortality, migration) are sufficient, it is possible to determine past population trends and establish predictive models. In the case of Western Chorus Frog, a complete population trend analysis would assess genetic flow and how it is influenced by connectivity within and among metapopulations. Where demographic data are missing and number of individuals cannot be estimated, as with the Western Chorus Frog (see below), it is possible to look at occupancy trends at the metapopulation or regional scale.
Auditory surveys are the most common method of anuran surveys. These surveys fall within two distinct groups: manual calling surveys (MCS) and automated recording systems (ARS). MCS involve observers listening to male frog vocalizations during a set period of time and for a given area (Dorcas et al. 2009). According to Dorcas and associates (2009), detection probability can vary according to factors such as abiotic and biotic conditions, and observer bias potentially leading to false negatives. Observer variability can also affect the quality of survey results and it is possible to incorrectly identify vocalizations leading to false positive results. These surveys are also limited to identifying the presence of males in an area and do not present a complete population structure nor quantify reproductive success. ARS are automated systems meant for intensive data collection in limited areas (Dorcas et al. 2009). Although biases associated with detection probability and observer variability can be lessened by this method, coverage of large areas is difficult and limitation associated with population structure and reproductive success remain.
Some auditory surveys use call density as an indicator of occupancy. This has limitations and can only be used to obtain qualitative abundance data through anuran calling indices (Dorcas et al. 2009). These indices exist for Western Chorus Frog at some sites but cannot be used to accurately describe population size. After a certain number of calling males (varies but generally 10 -20), calls overlap and individuals cannot be counted. For instance, when using a scale of 1 to 3, a score of 3 (i.e., full chorus, with calls of individuals indistinguishable [Dorcas et al. 2009]) could indicate any number from tens to thousands of calling males. As a result, the number of individuals at a pond having the highest chorus rank can vary greatly. Pond size can also influence the calling score; larger ponds may have higher calling scores because there are many males within detection range even though the density might be lower. Furthermore, within a metapopulation, ponds with low chorus scores, even over multiple years, can be needed to ensure connectivity between local ponds and resiliency of the metapopulation as a whole.
Available data for Western Chorus Frog are heterogeneous and reflect the level of research and conservation activities in the two provinces where the species occurs. The scale of the information is finer in Quebec, where the species is found in two localized regions of the province, than in Ontario, where the species is widespread provincially. In both provinces, however, survey data is based on MCS and do not estimate the number of individuals nor density. Western Chorus Frog population density at a given site can also vary from year to year for natural reasons. As such, true population trends cannot be calculated and suitable habitat availability paired with occupancy at a regional level is the best available surrogate.
1.5.2. Portrait of the Situation in Quebec
Analysis and Geographic Scale
In Quebec, change in habitat availability was determined by the variation in area of suitable habitat at two points in time (1991 and 2014 or 1992 and 2013 depending on data availability). To perform the analysis, all habitat within 300 m of all observation points Content Footnote2 within that timeframe was assessed as suitable or not suitable. Large water bodies, buildings, paved surfaces, intensive crops (e.g., corn, soy), and most areas covered with lawn including backyards and golf courses were considered unsuitable. This analysis was performed at the provincial scale for Ontario and Quebec, at the regional scale for Outaouais and Montérégie, and at the metapopulation scale for each metapopulation contained within the Montérégie region. Directly linked to the availability of habitat is habitat loss through destruction from threats. Number of sites destroyed is also presented when available.
To assess occupancy at the level of the metapopulation in Montérégie, comparison in the number of active breeding sites between years was used. Although the abundance and local distribution of Western Chorus Frog can vary inter-annually, results used compare two years of similar yet favorable environmental conditions thus reducing this bias (Picard 2015).
Within a metapopulation, connectivity among breeding ponds, which allows dispersal to new sites and re-establishment of previously extirpated sites, is an essential element of amphibian population dynamics (Semlitsch 2002). A loss of connectivity will directly impact the metapopulation structure, which in turn can compromise recovery and local survival. As such, connectivity and/or fragmentation and their impacts on the structure of populations at a regional scale and on a metapopulation basis were assessed in addition to habitat availability and occupancy whenever possible. Dispersal distances of individuals should be considered when assessing connectivity among breeding ponds and therefore the resiliency of a metapopulation to disturbances and changing environmental conditions. In a study of individuals tagged with Co60, a radioactive isotope, most were found to remain within 100 m of their breeding site; the greatest straight line distance travelled being 213 m (Kramer 1973). In another study (Whitaker 1971), all individuals captured in the summer were located within approximately 200 m of potential breeding sites. In Quebec, individuals were caught with drift fences as far as 200 m from the nesting sites (Whiting 2004). One study recommended that all suitable habitat within 300 m of breeding ponds be maintained to allow for the completion of the species' annual life cycle (Ouellet and Leheurteux 2007).
When comparing the amount of suitable habitat for Western Chorus Frog between 1992 and 2013 in Montérégie and between 1991 and 2014 in Outaouais, the analysis shows a decrease of suitable habitat of 13.1% (11.5 km2) within a 300 m radius of each Western Chorus Frog observation point for the province of Quebec as a whole.
Looking forward, the human population in Quebec is predicted to reach 9 million by 2027. This is an increase of almost 10% from 2014 (Institut de la statistique du Québec, 2014a). Such an increase in population can be expected to have impacts on the land, likely further limiting availability of habitat for Western Chorus Frog. In both regions where Western Chorus Frog are found, the predicted household growth (2011-2061) is superior to the provincial average (Institut de la statistique du Québec, 2014a).
In regions where the species occurs, suitable habitat is limited and, as noted below, declining. Wetlands cover only a small proportion of the landscape in Montérégie (578 km2 or 4.9%) and in Outaouais (3,263 km2 or 9.6%) (Pellerin and Poulin 2013), and these are under pressure from development. From November 2006 until March 2010, in Quebec, 558 permits were issued affecting 808 wetland areas covering 2,870 ha (Pellerin and Poulin 2013) with the majority being for residential projects. Of these permits, the Montérégie region received the highest number (142) while 21 were issued in the Outaouais region (Pellerin and Poulin 2013).
1.5.3. Portrait of the Situation in Outaouais
In Outaouais, the habitat trend analysis (1991- 2014) shows a decrease in suitable habitat for Western Chorus Frog of 7.4% (4.28 km2) (Table 1, Figure 3). Some areas, such as Gatineau, had more severe declines than others.
|Area name||Area of suitable habitat in 1991 (km2)||Area of suitable habitat in 2014 (km2)||Proportion of suitable habitat remaining in 2014|
Population growth in Outaouais will continue to put pressure on suitable habitat for Western Chorus Frog and therefore Western Chorus Frog metapopulations, many of which are found within urban areas. From 2011 until 2036, projections of population growth in the Outaouais region are estimated at 24% (Institut de la statistique du Québec 2014a). During the same period, the census metropolitan area of Gatineau is predicted to have the highest growth rate of any census metropolitan area in Quebec (Institut de la statistique du Québec 2014a). Taking into account these growth projections, the City of Gatineau published in 2011 predictions regarding the number of new housing units to be built. It is estimated that 30,000 new housing units would need to be built before 2031 (Ville de Gatineau 2011).
The agricultural landscape is more suitable to Western Chorus Frog in Outaouais than in Montérégie with almost 80% of cultivated areas being forage (MAPAQ 2013a). The surface area of cereal crop is increasing however (MAPAQ 2013a).
From 2004-2009, in Outaouais, a total of 346 Western Chorus Frog breeding sites were known from surveys (ÉRRFGOQ 2010). By 2009, 97 of these were destroyed and 30 were threatened and could be destroyed in the short term (ÉRRFGOQ 2010). Most of these (55 destroyed and 29 threatened) were found within urban or close to urban areas (ÉRRFGOQ 2010).
Since 2010, additional Western Chorus Frog breeding sites were destroyed as can be seen in raw survey data of the long-term monitoring surveys done by the Ministère des Forêts, de la Faune et des Parcs.
1.5.4. Portrait of the Situation in Montérégie
In Montérégie, the habitat trend analysis (1992- 2013) shows a decrease in Western Chorus Frog suitable habitat of 23.6% (7.26 km2) (Table 2, Figure 4, Figure 5). The metapopulation with the greatest decline is La Prairie. At some isolated populations (e.g., St-Chrysostome, Pin Rigide, Refuge Marguerite d'Youville), although substantial quantities of suitable habitat remain, Western Chorus Frog were not recorded in these areas in recent years. Furthermore, although some habitat might still have appeared as suitable during the geospatial analysis, it could have been destroyed by beaver or by habitat succession to closed canopy forests. In the Bois de Brossard–Sud and Boisé-du-Tremblay metapopulations, portions of the habitat that still seem suitable for Western Chorus Frog were identified by Picard (2015) as destroyed by beaver dams.
|Metapopulation or population||Area of suitable habitat in 1992 (km2)||Area of suitable habitat in 2013 (km2)||Proportion of suitable habitat remaining in 2013|
|Bois de Brossard Nord||2.86||2.86||100.0%|
|Bois de Brossard Sud||3.40||3.18||93.6%|
|Boisé de l'Amélanchier||0.53||0.43||82.0%|
|Boisé du Tremblay||7.41||5.80||78.2%|
|Boisé St-Bruno – Carignan||3.09||1.88||60.9%|
|La Prairie Table Footnotea||7.32||3.13||42.7%|
|Secteur Ligne Hertel/Lac Fontarabie/Rivière Saint-Jacques||3.67||3.42||93.1%|
Within this same time frame, the agricultural landscape within Western Chorus Frog range in Montérégie changed and contributed to the loss of Western Chorus Frog habitat. With soya and corn – both cultures being incompatible with Western Chorus Frog habitat – dominating the agricultural landscape of Montérégie (MAPAQ 2013b), forages have decreased from 13% to 11% and pastures declined from 2% to 1% (MAPAQ and CMM 2012).
Pressures on Western Chorus Frog habitat will continue to grow as more land is needed to accommodate human population growth. In Montérégie, the population growth from 2011-2036 is predicted at 21%, which is the second highest after Montreal (Institut de la statistique du Québec 2014a). When looking at households, Montérégie ranks first provincially with a projected increase of 157,000 households from 2011 to 2036 (Institut de la statistique du Québec 2014a). Population growth will affect every regional county municipality within which Western Chorus Frog are found (Institut de la statistique du Québec 2014b).
By 2009, the Western Chorus Frog had lost more than 90% of its historical range in Montérégie (ÉRRFGOQ 2010). At that time, nine metapopulations and seven isolated populations persisted in the region (ÉRRFGOQ 2010). This was a decline from previous years due to the loss of four metapopulations between 1994 and 2004 (Picard 2015). Owing to the important declines observed for the Saint-Hubert, Saint-Bruno and Bois de Brossard-Sud metapopulations during the 2014 surveys (Table 3), Picard suggests that only six of the previous nine metapopulations remain functional in Montérégie.
|Metapopulation name||Number of active breeding ponds in 2004||Number of breeding ponds destroyed by 2014 (%)||Number of active breeding ponds 2014 (% increase or decline compared to 2004)|
|Beauharnois||51||0 (0%)||75 (+47%)|
|Bois de Brossard-Nord||47||0 (0%)||32 (-32%)|
|Bois de Brossard-Sud||105||30 (29%)||14 (-87%)|
|Boisé du Tremblay||190||61 (32%)||96 (-49%)|
|Boucherville||168||45 (27%)||207 (+23%)|
|Île Perrot||52||16 (33%)||104 (+100%) Table Footnoteb|
|La Prairie||89||45 (51%)||128 (+44%) Table Footnotec|
|Saint-Bruno||18||5 (28%)||3 (-83%)|
|Saint-Hubert||37||10 (27%)||16 (-57%)|
1.5.5. La Prairie Metapopulation
For the La Prairie Western Chorus Frog metapopulation, the habitat trend analysis (1992- 2013) shows a decrease in Western Chorus Frog suitable habitat of 4.16 km2 (57.3%). Since 2013, at least an additional 0.22 km2 was destroyed by the construction of Phases 1, 2 and 3 of the Symbiocité (previously known as Domaine de la nature) residential project (Figure 6). When added to the 4.16 km2 of Western Chorus Frog habitat already lost, the rate of destruction is 60.2% within the last 23 years. Within the sizable extent of Western Chorus Frog habitat which remains southeast of Highway 30 in the population of Ligne Hertel/Lac Fontarabie/Rivière Saint-Jacques, the number of active breeding ponds recorded in 2004 and 2014 was limited to four (Picard 2015). These are believed to be remnants of previous populations now in decline or isolated individuals that dispersed from adjacent metapopulations (Picard 2015).
In the spring of 2004, surveys denoted a total of 89 Western Chorus Frog breeding ponds in the La Prairie metapopulation (Picard and Desroches 2004, Picard 2015). By September 2004, almost a third of these were destroyed (Picard and Desroches 2004, Picard 2015). By 2014, a total of 45 of these ponds had been destroyed (Picard 2015). Prior to 2004, declines were observed from partial surveys (1999-2003) where 12 of the 31 ponds known at the time were destroyed (Picard and Desroches 2004). In 2014, a total of 99 additional ponds were found bringing the total number of active ponds to 128 (Picard 2015). It is not always possible to assess whether additional ponds (newly recorded breeding ponds) are actually new ponds, heterocyclic ponds that were absent at the previous inventory, or pre-existing ponds that were not surveyed previously. Of the 99 additional ponds recorded in 2014, 79 were derived from the splitting of existing ponds and the creation of small ponds due to disturbances, 19 corresponded to an increase in the Western Chorus Frog population in the Grand Boisé Sud area, and only four were absent from previous inventories (Picard 2015).
From this, it is estimated that the decline in breeding ponds was 28.5% between 1999 and 2014 excluding 14 inactive ponds found in 2014 (Figure 7). For a number of reasons, certain ponds may not be used by Western Chorus Frog every year. Hence, non-occupancy of ponds formerly used by Western Chorus Frog is not necessarily an indication of local extirpation or that the population no longer uses this habitat. Prolonged non-occupancy can be caused by a number of factors including local/regional extirpation of the species; alterations in connectivity making the pond inaccessible; or a modification of the habitat's physiological or biological properties, making it suboptimal or even inadequate for reproduction. It is not possible to assess at this time if inactive breeding ponds surveyed in 2014 will remain permanently unoccupied. It should be noted that surveys conducted in 2004 and 2014 were exhaustive in nature and, as a result, data stemming from these surveys allowed for reliable comparison. In contrast, data obtained in 2015 were not as exhaustive and limited the breadth of comparison.
According to survey data from 2015, more than half of the current breeding ponds of the La Prairie metapopulation are found within the footprint of the Symbiocité residential project and its Parc de conservation du marais. The project area represents the core of the La Prairie Western Chorus Frog metapopulation. Within the area targeted by the project, 13 breeding ponds have been destroyed since the start of Phase 1 in July 2014 (Blais 2015a). These breeding ponds are not included in Figure 2 as 2014 surveys were conducted prior to their destruction. As of 2015, 66 active breeding ponds in total were still within the footprint of the project. According to inventories conducted in the spring of 2015, 34 of these active breeding ponds were within the Parc de conservation du marais, 10 located within Phases 1 through 4, and 22 within Phases 5 and 6 (see active breeding ponds in Figure 6). Further work within Phases 1 through 4 and Phases 5 and 6 directly threatens almost half of the remaining breeding ponds within the project area (see breeding ponds threatened by construction in Figure 6).
Connectivity Within the Metapopulation
Connectivity within the La Prairie metapopulation has been affected by breeding pond destruction from 2004 to 2014. Moreover, according to Picard (2015), a channel currently prevents dispersion of the species between Phases 1 through 4 and Phases 5 and 6 of the Symbiocité project and further limits connectivity (not shown in Figure 4). Some breeding ponds outside of the project area are already isolated from the core of the metapopulation (see isolated ponds in Figure 6). However, these isolated areas by themselves, cannot sustain the La Prairie metapopulation (described in more detail under Viability of the remaining breeding ponds section below). Without connectivity, metapopulations cannot subsist: breeding ponds become isolated from one another and are more susceptible to rapid decline and extirpation of Western Chorus Frog from them (Marsh and Trenham 2001). Furthermore, abundance of Western Chorus Frog was shown to be greater in ponds constituting a metapopulation than in isolated populations (Broadman 2009). Additional loss in breeding ponds due to the development of Phases 5 and 6 and further work within Phases 1 through 4 of the Symbiocité project can be expected to further degrade the connectivity and thus the functionality of this metapopulation (see breeding ponds threatened by construction in Figure 6).
Part of the connectivity left within the La Prairie metapopulation is maintained by the area targeted for development during Phases 5 and 6 of the Symbiocité residential project. Phases 5 and 6 of the project are at the boundary between the municipalities of La Prairie and Saint-Philippe. Ponds found within Phase II of the project allow connectivity between the Parc de conservation du marais and the ponds found in the Saint-Philippe municipality. The development of Phases 5 and 6 of the project would isolate most breeding ponds in Saint-Philippe from the rest of the metapopulation. Again, isolated ponds will be more susceptible to site specific disturbances and stochastic events leading to an increased chance of extirpation.
Viability of Remaining Breeding Ponds
Breeding ponds within the area targeted for development during Phases 5 and 6 of the Symbiocité residential project appear to be currently viable although some seem to have been altered by the start of work within the area. According to biologist Isabelle Picard (field observations, April 2015), hand dug canals at the northeast boundary between Phases 5 and 6 and the Parc de conservation du marais created drainage to surrounding ponds. Following inspection, the Ministère du Développement durable, de l'Environnement et de la Lutte contre les Changements climatiques, is of the opinion that changes in water level are more likely due to a particularly dry spring rather than to human-made changes to the hydrology of the area (Véronique Beauchemin pers. comm. 2015).
The undeveloped area within Phases 5 and 6 of the project as well as the remaining breeding ponds in Phase 4 are needed to maintain the viability of the La Prairie metapopulation because, as describe below, neither the Parc de conservation du marais nor the ponds outside of the Symbiocité residential project area can by themselves sustain the viability of this metapopulation should further development occur within the residential project.
Parc de conservation du marais
According to Blais (2015a), breeding ponds within the Parc de conservation du marais and in proximity to the Phases 5 and 6 area will be threatened by proximity drainage should the development of Phases 5 and 6 go ahead (among active breeding ponds, Figure 6). Some ponds at the north of the Parc de conservation du marais near route 104 and at the east where the stream was diverted are also threatened by drainage or were destroyed. The design of the Parc de conservation du marais does not allow sufficient area around most breeding ponds to ensure the long-term survival of Western Chorus Frog inhabiting these ponds (Picard 2015). A terrestrial area of 300 m around breeding ponds is required to allow for the completion of the species' annual life cycle (Ouellet and Leheurteux 2007). The design of the Parc de conservation du marais seems to have provided for a 50 m buffer around breeding ponds which is considered insufficient to meet the biological needs of Western Chorus Frog (Angers et al. 2008). Also, the park is irregularly shaped giving it a high perimeter / area ratio, hence decreasing the total area of suitable Western Chorus Frog habitat within the park free from edge impacts. Finally, the core area of the park will be further affected by a recreational path system, creating additional edge effect within the park. Considering the small number of active breeding ponds within the Parc de conservation du marais, the design of the area,and the potential impacts of Phases 5 and 6, it is unlikely that the Parc de conservation du marais, on its own, is sufficient to provide for the survival of the La Prairie metapopulation.
Ponds Outside the Symbiocité Residential Project
Breeding ponds outside of the Symbiocité residential project and its Parc de conservation du marais are also facing pressure and their viability is compromised. Some of them are already isolated meaning that, unless reconnected to the core of the metapopulation, these cannot contribute to the metapopulation dynamics. As such, these could not offer the rescue effect needed by the La Prairie metapopulation should Phases 4, 5, 6 of the Symbiocité project be developed.
- At the southeast end of the metapopulation and east of the Parc de conservation du marais is the industrial park of La Prairie where a few ponds are found (dark blue outline, figure 6) (Blais 2015b). These are isolated from the rest of the metapopulation. Most are located within a Hydro-Québec right-of-way (Blais 2015b), which are usually considered as compatible with Western Chorus Frog habitat. According to Blais (2015b), backfilling could however threaten them. The other pond is found within an industrial zoning and potential development within this area threatens its long-term viability (Blais 2015b).
- One isolated pond is found east of the Palerme boulevard and south of the 104 (green outline, figure 6). Given its location – beside a residential development and a quarry – and its low number, this pond's long-term viability is also compromised (Blais 2015b).
- South of the Candiac golf club is one pond (pink outline, figure 6) isolated from all other breeding ponds of the metapopulation due to its containment within a residential area. According to Blais (2015b) discharges of pool water from neighbouring properties or pesticide contamination are potential threats to this pond.
- To the northeast of the residential project are more isolated breeding ponds, some of which are found on the extension path of the Prés Vert boulevard and others within urban zoning of the La Prairie municipality (light blue outline, figure 6) (Blais 2015b).
Other ponds (black outline, Figure 6), situated to the south within the Saint-Philippe municipality, are still connected to the core of the metapopulation. This area is associated mainly with Phases 5 and 6 of the project, the construction of which would result in the loss of the connectivity between these ponds and the core of the Western Chorus Frog metapopulation. All these ponds are threatened to a certain extent according to Blais (2015b). These ponds could, for example, be lost to residential development or work on land property of the Ministère des Transports du Québec. These ponds alone are not sufficient to maintain the La Prairie metapopulation.
1.5.6. Portrait of the Situation in Ontario
220.127.116.11. Analyses and Geographic Scale
Status and trends in population and habitat were examined for Western Chorus Frog, where possible, at multiple geographic scales in order to better understand overall status and trends as well as localized trends resulting from threats that may be geographically concentrated. The three main scales of analyses in Ontario were:
- the Ontario portion of the Western Chorus Frog GLSLCS DU,
- faunal provinces (i.e., the Great Lakes/ St. Lawrence faunal province and the Canadian Shield faunal province), and
- Ontario 2011 census divisions defined by Statistics Canada (2012) (Figure 1).
As the species is widely distributed in Ontario, consistent data were not available at these different scales, and some data and information were applicable to only a portion of the range.
The decision to analyse by faunal province was partly owing to differences in data availability. There is more information available on Western Chorus Frog and its habitat within the Great Lakes/ St. Lawrence faunal province than within the Canadian Shield faunal province where there is a lack of information on habitat trends (e.g., wetland loss, land use change, agricultural intensification) and populations. Few surveys and monitoring routes have been conducted in the Canadian Shield portion of the range, and incidental records of the species are limited.
To capture localized trends, the census division scale was selected as several data sources were available at this scale (e.g., projected human population growth, agricultural trends, wetland loss) or could be summarized at this scale in Ontario. Records of the Western Chorus Frog (GLSLCS) occur in 39 Ontario census divisions (26 of these census divisions are fully contained within the Great Lakes/ St. Lawrence faunal province, 2 are fully contained within the Canadian Shield faunal province, 6 are split between the Great Lakes/ St. Lawrence and the Canadian Shield faunal provinces, and 5 split between the Great Lakes/ St. Lawrence and the Carolinian faunal provinces).
To further facilitate analysis of certain trends (i.e., land use change and threats from development of linear infrastructures) where Western Chorus Frog (GLSLCS) has been documented, "habitat units" were created by applying a 300 m Content Footnote3 radius around adequate Content Footnote4 Western Chorus Frog (GLSLCS) observations and merging together units with overlapping boundaries. This resulted in 1,433 habitat units totalling 53,307 ha in area (Figure 8; Appendix B- Table A).
18.104.22.168. Population Status
Enumeration of local populations
Previous reports have not provided an enumeration of local populations in Ontario, and element occurrences have not been defined because the species is not currently tracked by the Ontario Conservation Data Centre. As part of this science assessment, NatureServe guidelines for population/ element occurrence delineation (NatureServe 2015) were used to determine a coarse estimate of the number of local populations for the Ontario portion of the GLSLCS DU. Based on this analysis, roughly 389 local populations were identified in Ontario, of which 367 fall completely or partially within the Great Lakes/ St. Lawrence faunal province. This analysis was based on the best available data (not systematic surveys across the range) from 1975 until 2014, and results should be interpreted with caution. The estimated number of populations is likely an underestimation of the current distribution in Ontario.
There is little information regarding Western Chorus Frog populations across its full range in Ontario owing to a lack of systematic surveys and monitoring of the species in this province. A few studies in eastern Ontario (i.e., falling in the Renfrew, Ottawa, Prescott and Russell census divisions) have reported a decrease in the number of sites where the species has historically been present (Seburn and Gunson 2011; Seburn et al. 2008). These studies occurred in areas of habitat loss due to housing developments but do not take into account the fact that some adjacent breeding sites may have since been colonized.
Although true overall population trends have not been assessed for this species in Ontario, some analyses have been conducted at the scale of the DU and faunal provinces based on data collected through the Marsh Monitoring Program (MMP) Content Footnote5. As noted in the federal recovery strategy, the MMP data showed the number of occupied sites in the Great Lakes/ St. Lawrence faunal province decreased by 42.6% in Ontario over the period of 1995–1996 to 2005–2006 (Crewe et al. 2009).
To support this analysis, MMP data on the Western Chorus Frog in Ontario from 1995-2014 were analyzed to determine how the mean probability of Western Chorus Frog occurrence (or occurrence index) has changed over time (Table 4).
|Faunal Province(s)||MMP Trend
(mean probability of occurrence)
|Great Lakes/St. Lawrence||-2.9%/yr (-5.0, -0.7); statistically significant||Tozer 2015|
|Canadian Shield||Insufficient data||Tozer pers. comm. 2015|
|Great Lakes/St. Lawrence
AND Canadian Shield DU
|-2.6%/yr (-4.6, -0.5); statistically significant||Tozer pers. comm. 2015|
22.214.171.124. Habitat Status and Trends
Past changes in habitat availability and quality
Analysis of land use change
Southern Ontario Land Resource Information System version 2.0 (SOLRIS) change data (OMNRF 2015) were used to examine general changes in land use from 1999-2002 to 2009-2011. Land use changes were grouped based on whether they resulted in a potential suitable habitat gain or a potential habitat loss for the species. Land uses classified as potentially suitable habitat included woodlands, wetlands, water and undifferentiated lands, while land uses classified as likely unsuitable habitat included built-up areas, extraction and transportation. SOLRIS land use data is presented at a coarse resolution, and as a result, the ability to differentiate suitable vs. unsuitable habitat for Western Chorus Frog is limited (e.g., all types of agricultural lands are contained within "undifferentiated" land use type, and were therefore considered "potentially suitable" although certain types of agriculture, such as corn and soybeans, are not suitable for the species while pasture and old field agricultural lands are more commonly used by the species). The amount of potentially suitable habitat is therefore overestimated.
Approximately 58.5% of the Great Lakes/ St. Lawrence faunal province has SOLRIS coverage. Within this area, the overall loss of potential suitable habitat since 1999-2002 is estimated at 0.42%. When considering only area within the 300 m habitat units (around known records), the estimated loss of potential suitable habitat was 0.7%. There is no SOLRIS coverage for the Canadian Shield faunal province.
When analysed at the scale of entire census divisions (Appendix B- Table B), five census divisions showed more than 1% potential habitat loss: Peel (2.6%), Halton (2.2%), York (2.1%), Waterloo (1.5%), and Ottawa (1.3%).
Based on land use change within the 300 m habitat units alone, seven census divisions showed more than 1% potential loss: Middlesex (4.6%), Halton (2.0%), Ottawa (1.9%), Wellington (1.3%), York (1.3%), Toronto (1.0%), and Durham (1.0%).
Middlesex showed the highest potential loss at 4.6% (as compared to its census division result of 0.39%). Overall, however, estimates of potential loss were low in all census divisions but are suspected to be underestimated due to the resolution of analysis (e.g., old fields or pastures converted to intensive corn crops would not have been discerned as potential habitat loss).
Ducks Unlimited Canada (2010) performed an analysis to estimate wetland conversion for southern Ontario from pre-settlement to 1982 and 2002. The Southern Ontario study area (Appendix A – Figure B) is not representative of the full range of the GLSLCS DU; it covers the southern part of the Great Lakes/ St. Lawrence faunal province, but does not cover any of the Canadian Shield faunal province, and also includes the Carolinian faunal province (outside of the GLSLCS DU). In addition, the analysis was restricted to wetlands that are > 10 ha in size. Therefore, while it is a useful to get a general sense of rates of wetland loss (of permanent wetlands), many of the specific breeding habitats used by Western Chorus Frog (i.e., which include many small ephemeral wetlands) would not be captured in the analysis.
As of 2002, across the study area, only 28% of the pre-settlement wetland cover remained. Within the Great Lakes/ St. Lawrence portion of the study area, the decline in wetlands since settlement was most significant (85% of original wetlands converted) in parts of eastern Ontario and the Toronto area. Over the shorter term, across the entire southern Ontario study area, there was a 3.5% loss of wetlands between 1982 and 2002. Within the Golden Horseshoe Content Footnote6 wetlands were mainly lost to impervious and pervious built-up lands. Outside of the Golden Horseshoe wetlands were mainly converted to agriculture, urban brownfields, hydro right-of ways, edge of transportation corridors and clearings within forests (Ducks Unlimited Canada 2010).
Ducks Unlimited Canada (2010) also presented changes in total wetland cover between 1982 and 2002 at a county scale (corresponding in most areas to the census divisions) (Appendix B- Table C). The trend in wetland loss (1982-2002) was very high, high or moderate (relative to the trends in other areas with Western Chorus Frog) in the following counties/ census divisions:
- Very High: Lanark (19.7%) and Frontenac (17.3%);
- High: Stormont (9.3%), Glengarry (part of the Stormont, Dundas and Glengarry census division) (8.1%), Lennox and Addington (8.1%), Hastings (7.3%);
- Moderate: Dundas (part of the Stormont, Dundas and Glengarry census division) (5.8%) and Durham (5.5%).
One of the primary threats to Western Chorus Frog habitat is agricultural intensification. Suitable habitat for the Western Chorus Frog, primarily small ephemeral wetlands, is often lost due to the expansion of agricultural lands (Seburn et al. 2014) and habitat connectivity can be reduced. In the area east of Ottawa and north of Renfrew, Western Chorus Frog has disappeared from large areas where the only apparent change in land use was agricultural intensification (Schueler and Karstad 2012). In this component of the analysis, general trends in agricultural intensification will be analysed using recent literature and agricultural census data. Agricultural intensification may feature higher pesticide and fertilizer inputs, larger farm sizes and higher farm capitalization.
The percent of Ontario's land cover (entire province) occupied by agricultural lands declined from 10.1% in 1931 to 5.6% in 2011 (Smith 2015). For southern Ontario (Appendix A - Figure C) specifically, which includes the southern portion of the Great Lakes/ St. Lawrence faunal province in addition to the Carolinian faunal province, this represents a decline from 60.7% in 1931 to 35.5% in 2011 (Smith 2015). The decrease is primarily composed of decreased farm ownership of pasture, woodlands and wetlands and other non-production lands (Smith 2015). Although suitable habitat for the Western Chorus Frog is threatened by agricultural intensification, the species uses some types of agricultural land cover including old field and pasture (Seburn et al. 2014). In eastern Ontario the amount of pasture decreased from a range of 20-30% in 1971 to 2-5% in 2001. Similarly, a decrease in the amount of pasture was noted in some townships in Bruce County from 30-40% in 1971 to 5-10% in 2001 (Neave and Baldwin 2011). Old field/ shrubland also declined from a range of 10-20% in 1971 along the Frontenac Arch and west to Peterborough to 5-10% in 2001 (Neave and Baldwin 2011). Significant long-term declines in total pasture are expected to continue (Smith 2015).
Since 1960, agricultural land cover in Ontario has also experienced an increase in grain corn and soybeans (Joseph and Keddie 1981; Small 1999; Keddie and Wandel 2001). More recently there is evidence that some hedgerows, forests and small wetlands are undergoing conversion to annual crops (Smith 2015). Increase of monocultures and a loss of agriculture types that support the Western Chorus Frog is a significant threat to the species in Ontario.
Pesticides and Fertilizers
Pesticide use (insecticide, herbicide and fungicide) decreased in Ontario by more than 45% from 1983-2008 (Smith 2015). The decrease in pesticide use is attributed to multiple factors including incentives for integrated pest management, changes in production, increasing cost of pesticides and pest resistant varieties (Gallivan et al. 2001; Government of Ontario 2003; McGee et al. 2010). There is also a decreasing trend in fertilizer use from 1980-2000 (Smith 2015). Therefore, the degree of habitat degradation for Western Chorus Frog resulting from pesticides and fertilizers may likewise be decreasing overtime.
Anticipated impacts from human population growth and development projects
Human population growth and anticipated urban development
Urban development is a primary threat to the Western Chorus Frog that results in the degradation and loss of suitable habitat. Mapping or precise locations of future urban development projects are not readily available across the range of the Western Chorus Frog in Ontario. Therefore, this analysis uses projected human population growth at the scale of the census divisions as a surrogate/ predictor for future urban development (i.e., increased population growth can be expected to result in increased urban development).
Long term population projections for Ontario census divisions were produced by the Ontario Ministry of Finance (2014) based on the 2011 Census of Canada. Using the population in 2013 as a baseline, projected percent population growth was calculated for 2016, 2021, 2026, 2031 and 2041 (Ontario Ministry of Finance 2014; Appendix B - Table D). Census divisions with highest trend in population growth (from 2013 to 2021) in the GLSLCS region were: Halton (17.6%), York (16.2%), Peel (14.3%), Ottawa (11.8%), and Durham (11.1%).
Using projected population growth as a surrogate for anticipated urban development, it can be assumed that the census divisions listed above will also experience a high trend in urban development relative to the other census divisions within the GLSLCS region.
For the GLSLCS DU as a whole (based on all census divisions partially or fully within the GLSLCS) the 2013 human population was over 12 million, and this population is projected to grow by 3.3% by 2016 and 9.4% by 2021.
Expansion and Maintenance of Linear Infrastructure
As noted in the federal recovery strategy, the expansion and maintenance of linear infrastructures such as roads and utility and pipeline right-of-ways is a threat to the Western Chorus Frog throughout its range. In addition to resulting in direct mortality of individuals (e.g., road mortality) and the spread of invasive plant species, linear infrastructures can act as barriers to dispersal and thus contribute to habitat fragmentation or result in a loss of habitat entirely (i.e., loss of breeding ponds within metapopulation range). It should be noted, however, that maintenance of infrastructure can benefit local populations when conducted in the appropriate period that favours the maintenance of suitable habitat conditions.
All proposed or known projects either within the census division containing Western Chorus Frog records, within 1 km of a Western Chorus Frog occurrence or within 300 m of a Western Chorus Frog occurrence were compiled. The majority of these are large projects that were identified through searches of current federal Environmental Assessments (EAs). Five projects were within 300 m of a Western Chorus Frog occurrence, six additional projects were within 1 km of a Western Chorus Frog occurrence, and five additional projects were outside of a 1km radius of Western Chorus Frog but within a census division that contains the species (Table 5). The projects within 300 m of a Western Chorus Frog occurrence include oil and gas pipelines (one in York, another in both York and Toronto and a third spans from Sarnia to Montreal) and transportation corridors (roadways, transit and rail; one project in York and a second in Halton, Peel and York). It is possible that other linear projects (especially smaller roads) that do not trigger a federal EA may also be planned in the range and be additive to those described here.
|Project Name/Status||Source||Intersect (within 300 m WCF)||Nearby (within 1 km WCF)||Census Division|
|Highway 69 Twinning||EA||No||No||Sudbury, Parry Sound|
|Enbridge Line 9 Reversal-under construction||EA||Yes||Yes||Sarnia to Montreal|
|Energy East Pipeline||EA||No||Yes||Stormont, Dundas and Glengarry|
|Eastern Mainline Pipeline||EA||Unknown||Yes||York, Durham, Northumberland, Hastings, Lennox and Addington, Frontenac, Leeds and Grenville, Stormont, Dundas and Glengarry.|
|CN Rail Milton Logistics Hub-CEAA Panel||EA||No||Yes||Halton|
|GTA West Transportation Corridor-pending CEAA EA||EA||Yes (Peel and York)||Yes||Halton, Peel, York|
|TransCanada Vaughan Mainline Extension||EA||Yes||Yes||York|
|TransCanada Kings North Connection Pipeline||EA||Yes||Yes||York, Toronto|
|Enbridge Line 10 Pipeline Replacement||EA||No||Yes||Hamilton|
|Enbridge Canadian Nuclear Laboratories Chalk River Facility Pipeline (sec. 67)||EA||No||No||Renfrew|
|North Kanata Trunk Sewer (sec. 67)||EA||No||Yes||Ottawa|
|NCC - New Pathway from Tauvette Street to the Rail Trail Corridor (sec. 67)||EA||No||No||Ottawa|
|Highway 427 Expansion||Other||Yes||Yes||York|
126.96.36.199. Overall Noteworthy Areas And/ or Areas of Concern in Ontario
The census divisions listed below have been identified as areas of potential interest and/or concern in considering the following information from this assessment:
- A large number/area of Western Chorus Frog habitat units;
- Significant apparent loss or degradation of habitat (past) and/or significant anticipated threats from future development projects (urban or linear)
Census divisions with the greatest number and/or area (ha) of habitat units include: Peterborough, Leeds and Grenville, Prince Edward County, Ottawa, York, and Lanark.
Trends for habitat loss (SOLRIS land use change), wetland loss, anticipated urban development (human population growth) and agricultural intensification were ranked for each of the regions identified above and linear infrastructure projects were also considered. Peterborough, Leeds and Grenville, and Prince Edward County did not rank high for any of the threat analyses. Ottawa ranked high for habitat loss and anticipated urban development. York ranks high for habitat loss and anticipated urban development, and there are also several known and proposed linear infrastructure projects within the York census division. Lanark experienced high wetland loss (percent of county) 1982-2002.
Areas that did not rank highest in terms number and/or area of Western Chorus Frog habitat units, yet where significant apparent loss or degradation of suitable habitat and/ or significant anticipated threats from future development or linear projects include:
- Durham (habitat loss and urban development)
- Frontenac (wetland loss and urban development)
- Halton (habitat loss, urban development and future development projects)
- Hamilton (habitat loss and future development projects)
- Middlesex (habitat loss, wetland loss and urban development)
- Peel (habitat loss, urban development and future development projects)
- Prescott and Russell (urban development)
- Simcoe (habitat loss, urban development and future development projects)
- Toronto (habitat loss, urban development and future development projects)
- Waterloo (habitat loss and urban development)
- Wellington (habitat loss and urban development)
Widespread declines in Western Chorus Frog have already been observed in Ottawa, Renfrew and Prescott and Russell (Schueler and Karstad 2012; Seburn et al. 2008, 2014; Seburn and Gunson 2011).
1.6. Capability to Create Western Chorus Frog Habitat and a New Metapopulation
The likelihood of success in creating or moving a metapopulation appears to be low, or at least difficult to predict. Although there is an existing guide on habitat creation and monitoring for the Western Chorus Frog (Montpetit et al. 2010), it focuses on measures aimed at enhancing connectivity between Western Chorus Frog populations and metapopulations, rather than on the creation of a disjunct metapopulation. With respect to colonization of created sites by the Western Chorus Frog, the guide recommends natural colonization, which requires that a created site be located near a site already occupied by the species (within 250 m of it) and that there be no obstacles to movement (e.g., roads, watercourses, walls). Human-mediated translocation of individuals or eggs from an occupied site to a created site is not recommended, because of the low rate of success observed in amphibian translocations (Desroches and Picard 2004), an approach which is still experimental, and because of the considerable effort involved in capturing and relocating a large number of individuals or eggs over a period of several years (Montpetit et al. 2010; Tessier et al. 2015). The risk of pathogen introduction and spread and the potential for homing (return of relocated individuals to their natal site) are also problems that may arise in connection with the translocation of amphibians. In addition, uncertainty exists regarding the minimum number of individuals needed to establish a viable population; several tens of thousands of eggs or larvae would probably be needed over a number of consecutive years (Desroches and Picard 2004). The release of captive-reared individuals (e.g., under the pilot project developed by the Montreal Biodome and the Ecomuseum Zoo [Jacques Dancosse, pers. comm.]) is not recommended in the present context either, because of the individuals' origin and low genetic diversity, but also because of the present lack of knowledge about the fate of released individuals (e.g., survival and ability to reproduce in the natural environment). It should also be noted that a study involving the genetic characterization of Western Chorus Frog populations in Quebec and Ontario has revealed the presence of genetically distinct conservation units in both provinces, particularly in Montérégie (N. Tessier, pers. comm. and article in preparation, cited in Tessier et al. 2015). The genetic differences between the populations and metapopulations in Montérégie could be indicative of local adaptations (e.g., escape from predators or resistance to pathogens); this would make it risky to translocate individuals to a given habitat to which they are not adapted.
Attempts to create Western Chorus Frog habitat in Quebec have been made in the past, with very limited success. Indeed, it was reported that only 4 of 32 created habitats visited in 2014 presented characteristics favourable for Western Chorus Frog reproduction (Tessier et al. 2015). Some of the problems encountered include the permanent (non-temporary) character of certain wetlands, the presence of Western Chorus Frog predators, high water temperatures in July, premature habitat drying, excessive canopy closure, and the colonization of ponds by invasive plants. These characteristics show that the Western Chorus Frog is not a generalist species and that it has very specific habitat needs about which not enough is known, making it difficult to create suitable habitat. On the basis of field observations, Tessier et al. (2015) proposed a number of modifications to the guide written by Montpetit et al. (2010), without any guarantee that the changes would lead to a higher success rate. Moreover, a project was initiated in 2015 within the Saint-Bruno metapopulation, with the aim of eventually creating habitat suitable for the species by taking into account parameters that influence the hydrology of the environment and the species' dispersal ability (MFFP, pers. comm.); the results of this project are not yet known.
Therefore, while habitat creation methods for the Western Chorus Frog do exist, the rate of success was very low in the past and these methods are aimed at increasing habitat area and enhancing connectivity between populations and metapopulations by capitalizing on natural colonization by individuals, rather than creating or moving a population or metapopulation.
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Appendix A - Figures:
Ontario 2011 Census Divisions
Study Area for Wetland Loss
Appendix B - Tables:
|Census Division||Habitat Units
% of Total Area
Number of units (or portions of units)
|Critical Habitat Units
|Critical Habitat Units
% of Total Area
|Critical Habitat Units
Number of units (or portions of units)
|Leeds and Grenville||6,062||11.4||159||2,785||16.7||46|
|Lennox and Addington||1,010||1.9||31||137||0.8||5|
|Prescott and Russell||216||0.4||6||27||0.2||1|
|Stormont, Dundas and Glengarry||1,065||2.0||32||134||0.8||3|
|-||-||-||(number of units = 1433)||-||-||(number of units = 218)|
4.2. Land Use Change
|Census Division (CD)||CD Area (ha)||SOLRIS Coverage
Area (ha) without coverage
Area (ha) with coverage
Percent of CD with SOLRIS Coverage
|SOLRIS Change (by percent of total area of SOLRIS coverage)
Potential Habitat Loss
|SOLRIS Change (by percent of total area of SOLRIS coverage)
No gain/ loss likely (remains potentially suitable)
|SOLRIS Change (by percent of total area of SOLRIS coverage)
No gain/ loss likely (remains likely unsuitable)
|SOLRIS Change (by percent of total area of SOLRIS coverage)
Potential Habitat Gain
|Prescott and Russell||206,972||-||206,972||100||0.32||0.34||0.00||0.00|
|Leeds and Grenville||360,954||24,455||336,499||93||0.11||0.10||0.00||0.01|
|Stormont, Dundas and Glengarry||332,308||-||332,308||100||0.10||0.41||0.00||0.01|
|Lennox and Addington||297,821||170,330||127,491||43||0.09||0.00||0.01||0.00|
|County||Wetlands Lost by 1967 – Area (Ha)||Wetlands Lost by 1967 - % of County||Wetlands Lost by 1982 – Area (Ha)||Wetlands Lost by 1982 - % of County||Wetlands Lost by 2002 - Area (Ha)||Wetlands Lost by 2002 - % of County||Trend in Wetland Loss (% of county) 1982-2002|
|Lennox and Addington||26334||68.6%||24220||63.1%||27333||71.2%||-8.1%|
Projected Population Growth
Historical Population (in 1000's)
Projected Population (in 1000's)
Projected Population (in 1000's)
Projected Population (in 1000's)
Population Growth Trend by Census Division 2013-2041
Population Growth Trend by Census Division 2013-2041
Population Growth Trend by Census Division 2013-2041
|Prescott & Russell||89.3||91.5||95.9||108.4||2.50%||7.40%||21.40%|
|Lennox & Addington||44.4||45.1||46.1||48.2||1.60%||3.80%||8.60%|
|Leeds & Grenville||101.9||102.5||104.1||107.5||0.60%||2.20%||5.50%|
|Stormont, Dundas & Glengarry||115.4||115.2||115.2||111.7||-0.20%||-0.20%||-3.20%|
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