Blanding's turtle COSEWIC assessment and status report: chapter 7

Habitat

Habitat Requirements

The Blanding’s Turtle is a largely aquatic turtle that occurs in a variety of wetland habitats including lakes, permanent  ponds, temporary ponds, slow flowing brooks, creeks, marshes, river sloughs, marshy meadows, man-made channels, farm fields, coastal areas and the bays of Lake Erie (Kofron and Schreiber 1985; Petokas 1986; Rowe 1987; Ross and Anderson 1990; Rowe and Moll 1991; Pappas and Brecke 1992; Ernst et al. 1994; Power et al. 1994; Herman et al. 1995; Joyal et al. 2001; Gillingwater and Brooks 2001, 2002). In general, the preferred wetlands occupied by the Blanding’s Turtle are eutrophic, and are characterized by shallow water with an organic substrate and high density of aquatic vegetation (Ernst et al. 1994; Herman et al. 1995). Occasionally, individuals can be found inhabiting upland wooded areas.

Blanding’s Turtles will travel seasonally over land between aquatic areas (Ruben et al. 2001) to locate suitable basking and nesting sites (Joyal et al. 2001; Bury and Germano 2002; Semlitsch and Brody 2003). Despite these seasonal movements, Blanding’s Turtles have strong site fidelity (Piepgras and Lang 2000). In Nova Scotia, they are often associated with peaty soils and coloured water as these areas tend to have higher secondary productivity than do clear waters in this region (Power et al. 1994). Beaver activity is present at most Blanding’s Turtle sites in Nova Scotia, and is believed to play an important role in water level control (Herman et al. 2003).

Suitable basking sites must be present where the turtle can remove itself from the water and gain access to direct sunlight. These basking sites can be partially submerged logs, rocks, bog mats, or suitable shoreline. Blanding’s Turtles may also bask in open areas while travelling over land through upland wooded areas (Joyal et al. 2001). Juveniles bask on sphagnum mats (McMaster and Herman 2000), emergent sedges, in alder swale, and in shallow water surrounding emergent root masses (Pappas and Brecke 1992). The vegetation around water bodies favoured by Blanding’s Turtles can vary to a great degree, but usually consists of plants that thrive in highly eutrophic conditions.

Adult turtles overwinter in permanent bodies of water (Joyal et al. 2001) and, in some cases, seasonally isolated wet depressions or ponds (Power 1989). Turtles will densely aggregate in overwintering sites in Québec (St-Hilaire 2003) and in Nova Scotia, with up to 14 individuals at a single site (Herman et al. 2003). In Nova Scotia, individuals tend to return to the same sites each year (Herman et al 2003). During the winter months, the Blanding’s Turtles do move, although only in limited amounts (a few metres) (Ernst et al. 1994). Over the majority of the range very little is known about the overwintering requirements of the Blanding’s Turtle.

Terrestrial habitat is also important, as these turtles will travel overland more than 2.5 km to nest (Jennifer McNeil, Tom Herman, pers. comm. Jan 24, 2005), and will nest up to 410m from the nearest water source (Joyal et al. 2001). Terrestrial habitat is generally upland wooded areas, consisting of mixed deciduous or coniferous forest.

Adults

Adult Blanding’s Turtles require both aquatic and terrestrial habitats. In southern Maine, they prefer permanent ponds and lakes (Joyal et al. 2001), and in Nebraska, adult turtles spend over 50% of their time in these habitats (Bury and Germano 2002). It is thought that these permanent bodies of water offer an abundance of food. Less cover and refugia are required for adults since they are less susceptible to predation than juveniles. Adult Blanding’s Turtles will use multiple bodies of water throughout the active season, travelling upwards of 6760m during an active season in southern Maine (Joyal et al. 2001), presumably to locate food or a mate. During spring, adult females travel up to 1620 m in Maine (Joyal et al. 2001), and up to 7000 m in Nova Scotia (Jennifer McNeil, pers. comm. Jan 24, 2005) to nest. In Nova Scotia, Blanding’s Turtles primarily occupy beaver-regulated wetlands associated with small streams or adjacent lakeshores (Herman et al. 2003). On Pelee Island, adults utilize the canal system and inland wetlands more often, and are not often observed making use of coastal Lake Erie habitats (Ben Porchuk pers. comm. April 1, 2005). In Québec, one female travelled 1700m between her nesting site and summer habitat, and another travelled almost 2000 m to reach hibernacula (St-Hilaire 2003).

Juveniles

Juveniles spend the majority of their time in marsh habitat in Nebraska (Bury and Germano 2002), southern Maine (Joyal et al. 2001), and Minnesota (Pappas and Brecke 1992). This habitat presumably offers increased opportunities for refuge, decreasing the potential of predation. Juveniles are more susceptible to predation due to their small size, and thus require a greater availability of refugia to increase their chances of survival. Pappas and Brecke (1992) in Weaver Dunes of Wabasha County Minnesota, suggest that Blanding’s Turtles with a carapace length less than 100mm prefer habitat that has an abundance of cover and stay close to the water’s edge where vegetation offers considerably more refuge than does open water. Turtles with a carapace length greater than 100 mm inhabited open water microhabitats more often.

Juvenile Blanding’s Turtles in Nova Scotia are found in similar areas as adults, but again occupy different microhabitats and show seasonal differences in distribution (McMaster and Herman 2000). Juveniles are most often associated with floating sphagnum mats and abundant shrub cover. McMaster and Herman (2000) found that young juveniles (age 1-7 years) were more often visible than older juveniles (age 11-13), which seems to contradict the hypothesis that younger turtles seek more cover to avoid predation.

Hatchlings

Hatchlings emerge from their nests in late September and early October (Standing et al. 1999; Herman et al. 2003). Nests are usually laid in loose sand and organic soil throughout most of the species’ range. However, in Nova Scotia, females primarily nest on cobble lakeshore beaches and rocky outcrops of freeze-fractured material, and secondarily use roadside gravel. Some turtles must travel more than 200m from nest to water in Nova Scotia (Standing et al. 1999), and more than 400m in southern Maine (Joyal et al. 2001). This large distance from nest to water may be why some hatchlings will overnight terrestrially. As a result of spending nights on land, hatchling Blanding’s Turtles may be susceptible to increased mortality rates from mammalian and avian predators.

Once hatchlings reach a body of water, they occupy fringe habitat never straying far from cover provided by aquatic vegetation, partially submerged floating logs, or terrestrial vegetation that has grown over the water surface. Characteristically, the most obvious feature of suitable juvenile habitat is dense Sphagnum moss growth with overlying vegetation (McMaster and Herman 2000). The fact that hatchlings are frequently found hiding under floating organic cover (Pappas and Brecke 1992) may contribute to the low occurrence of reported sightings. However, a more accepted and probable explanation for the low occurrence of sightings is a high nest failure rate (Congdon et al. 1983) and a low annual survivorship, among hatchlings and juveniles because they are more susceptible to predation (Pappas and Brecke 1992).

Overwintering sites for hatchlings remain unknown. In Nova Scotia, studies of hatchling movement patterns shortly after nest emergence indicate that most hatchlings do not immediately seek water, raising the possibility that they may overwinter terrestrially (Standing et al. 1997; McNeil et al. 2000). In a recent laboratory study of cold hardiness and dehydration resistance of hatchling Blanding’s Turtles from Nebraska, Dinkelacker et al. (2004) concluded that terrestrial overwintering may be possible if the habitat remains moist enough to prevent dehydration. Although there have been no reports of hatchlings hibernating on land, it does appear to be a possibility, but it is probably not commonplace.


Habitat Trends

Wetland habitat in southern Ontario and Québec has undergone continued drainage and development since the early 1800s. This continued destruction threatens the sustainability of the Great Lakes/St. Lawrence Blanding’s Turtle populations. Development results in increased traffic on existing roadways, as well as the creation of new roadways. Road-killed turtles have been reported all across south-central Ontario (Bob Johnson, Constance Browne, Mike Hall, John Haggeman, Kim Barrett, Glenda Clayton, Lauren Trute, David and Carolyn Seburn, Sandy Dobbyn, pers. comm. May 25, 2004; Jim Trottier, pers. comm. May 31, 2004; Chris Burns, pers. comm. June 4, 2004; Angie Horner, pers. comm. June 6, 2004; Joël Bonin, pers. comm. June 9, 2004; Ben Porchuk pers. comm. April 1, 2005), as well as in Québec (St-Hilaire 2003; Desrochers and Picard 2005). Additionally, Blanding’s Turtles often nest on the gravel shoulders of roads (Standing et al. 1999), putting not only nesting females, but also emerging hatchlings at risk.

Furthermore, the rapid development of suitable habitat fragments Blanding’s Turtle habitats and populations, isolating them, and preventing any natural rescue effect from other populations. In the Metropolitan Toronto area, there are still four very small “populations” (Bob Johnson, pers. comm. June 7, 2004). It can be assumed that these populations are now reproductively isolated from one another by commercial and residential developments. The absence of juvenile sightings or reports of nesting females from the Metropolitan Toronto area indicates that suitable nesting sites have most likely been degraded or destroyed and/or there is no successful recruitment. As more suitable habitat is consumed by urban sprawl, one can expect similar fragmentation in other areas in Ontario, as well as in Québec.

In Nova Scotia, the two principal changes in habitat since European colonization have been increased fragmentation of forests and alteration of water flow regimes (primarily for power generation); both have almost certainly had profound effects on turtles (Herman et al. 2003). Changes in water flow regimes are a particular concern as they may impede seasonal movements and affect the turtles’ ability to nest, feed, and access overwintering sites (Herman et al. 2003). Increased human activity associated with roads, cottage development, and agriculture has increased habitat fragmentation and degradation.


Habitat Protection/Ownership

Blanding’s Turtle habitat in Ontario and Québec is protected by many Provincial Parks (P.P.), National Parks (N.P.), and National Wildlife Areas (N.W.A.) including Rondeau P.P., Killarney P.P., Algonquin P.P., Long Point P.P., Gatineau P.P., Point Pelee N.P., Georgian Bay Islands N.P. Big Creek N.W.A., Long Point N.W.A., and Lake St. Clair N.W.A. These areas provide essential habitat protection within park boundaries, although they are not continuous with one another, and as a result may not be sufficient to ultimately offer protection. The ability for these parks to serve as refugia is questionable; the fact that they are not continuous means they do not facilitate the movement of individual turtles from one park to another. In addition, the development of road networks in these parks contributes to increased mortality of Blanding’s Turtles (Ashley and Robinson 1996; Gillingwater and Brooks 2001, 2002; Norm Quinn, pers. comm. May 25, 2004). Local populations of Blanding’s Turtles within park boundaries may still be declining, as is the case in Kejimkujik N.P. (Jennifer McNeil, Tom Herman pers. comm. Jan. 24, 2005), and in Point Pelee N.P. (Constance Browne, pers. comm. May 25, 2004), or may only be a relict population of an aging cohort (Ben Porchuk April 1, 2005).

In Nova Scotia, one subpopulation is located primarily within Kejimkujik National Park and National Historic Site. The other two subpopulations are in working landscapes. At McGowan Lake, in 2003, a substantial portion of critical habitat (102 ha) was protected by the local forestry company that owned it. An additional 700ha was protected by the provincial government in 2004. Although this action protects much of the McGowan Lake subpopulation, additional areas on private land, including a critical overwintering area, remain unprotected (Tom Herman, pers comm. Jan. 24, 2005). The Pleasant River subpopulation, where land is mostly privately owned and subjected to an array of uses, has been the focus of an intensive community level stewardship campaign in the past two years (Caverhill in progress; as cited by Tom Herman and Jennifer McNeil, pers. comm. Jan. 24, 2005). (Nova Scotia information supplied by Tom Herman and Jennifer McNeil, pers. comm. Jan. 24, 2005.)

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