Intraspecific and interspecific variation in use of forest-edge habitat by snakes

Abstract

Variation in use of edge habitat among populations and species of snakes should reflect underlying causes (e.g., thermal ecology, prey availability) and consequences (e.g., predation on birds' nests) of habitat selection. We compared the habitat use of ratsnakes, Elaphe obsoleta (Say in James, 1823), in Illinois and Ontario and compared habitat use by ratsnakes and racers, Coluber constrictor (L., 1758), in Illinois. Ratsnakes in Illinois used upland forest more and forest edges less than ratsnakes in Ontario. Female ratsnakes in Illinois used edges less than males, regardless of their reproductive status. Relative to ratsnakes, racers preferred forest edges and avoided forest interior. Female racers used edges more than males, especially while gravid. These results, and most of the seasonal patterns in habitat use, were broadly consistent with variation expected from differences in thermoregulatory needs, although other factors potentially influencing habitat use cannot be ruled out. Although it has been proposed that some forest fragmentation is likely to be beneficial for ratsnakes in Canada, such fragmentation may be detrimental to ratsnakes in Illinois but beneficial to racers. Thus, relative to forest-interior species, edge-nesting birds should be more vulnerable to predation by ratsnakes in Ontario, and fragmentation should increase the vulnerability of forest birds to nest predation by racers.

Sources of variation in the nesting success of understory tropical birds

“…In tropical Australia, however, weather related variables within a season explained little variation in snake activity patterns and feeding rates (Brown and Shine 2002). Studies of the thermal ecology of snakes using telemetry have revealed much about the factors that affect their encounter rates with nests in North America (Carfagno and Weatherhead 2006, 2008). We believe that similar studies of predator activity (snakes or otherwise) in tropical habitats offer opportunities to further understand temporal, spatial, and interspecific variation in rates of nest predation on birds.…”

Role of topography, canopy structure, and floristics in nest-site selection and nesting success of canopy songbirds

“…Although the model containing all red oak species had the strongest support, there was some support for individual oak species such as Q. velutina found on xeric ridgetops. Hotter, drier microclimates in upland areas may be used by predators such as the black rat snake (Elaphe obsoleta) (Carfagno and Weatherhead, 2006), and a black rat snake was directly observed depredating a Cerulean Warbler nest 28 m up in a large Q. velutina tree at ZSF (F. Newell, personal observation). Using parental behavior to find nests (Mullin and Cooper, 1998) Blue Jays (Cyanocitta cristata) were likely another important nest predator in our system, which may have contributed to low nesting success even in a predominantly forested region.…”

Habitat selection by grassland snakes at northern range limits: Implications for conservation

“…The racer meets the criteria to be listed as Endangered, but it was designated as Threatened because GNP protects most of its known range in the country (COSEWIC 2004). Very little research has been conducted on C. c. flaviventris in North America; however, several studies investigate habitat use of closely related subspecies (e.g., Rosen 1991, Plummer and Congdon 1994, Carfagno and Weatherhead 2006).…”