Hibernation and Oviposition Sites of Great Basin Gophersnakes (Pituophis catenifer deserticola) near Their Northern Range Limit
Northern range limits for snakes may result from thermal constraints, especially for oviposition and hibernation. We characterized hibernation and oviposition sites for federally threatened Great Basin Gophersnakes (Pituophis catenifer deserticola) near the edge of their northern-range limit in south central British Columbia, Canada. During 2006 and 2007, most Gophersnakes (75.8%) hibernated alone. At our more northern study area, typical hibernation sites were in grassy hillsides, whereas at our southern study areas snakes hibernated in rocky outcrops. All snakes that denned in rock outcrops reused sites over years, but only 28.6% of snakes that hibernated in rodent burrows reused sites. Most female Gophersnakes (94%) laid eggs in sites that were not used by other females, and reuse of sites was rare (12.5%). Almost all of the oviposition sites were in grassy slopes, with any shrubs and trees more than 5 m away; females selected grassy or sage-steppe cover for oviposition. This pattern of mostly individual and single-use hibernation and oviposition sites suggests that hibernation and oviposition sites are readily available as components of the active-season range within the sage-steppe ecozone, although this habitat is rare and severely threatened within Canada. In terms of species conservation, areas of suitable habitat should be protected based on active-season use, rather than by attempting to find hibernation sites supporting large aggregations of snakes. This recommendation is unlike that for Rattlesnakes (Crotalus spp.) and Gartersnakes (Thamnophis spp.), which often congregate at hibernation sites.Abstract
The location of the study areas within south-central British Columbia, Canada.
Number of Great Basin Gophersnakes occupying communal and single hibernation sites in 2006 or 2007 by study area in the Okanagan Valley, British Columbia. Only one snake, from Vernon, used both a communal hibernation site and a single hibernation site—this snake was recorded on this graph only once, as belonging to a communal hibernation site.
Soil textures at oviposition sites of Great Basin Gophersnakes and available at the study areas. We sampled 40 random soil sites to determine availability, and in 2007 we assessed soil textures at eight oviposition sites. The asterisks indicate soil types that female Gophersnakes selected (Manly's α = 0.19 for loamy sand, 0.22 for silty loam, and 0.44 for sandy loam; the threshold for selection is 0.14); the other four soil types were avoided.
Average maximum daily temperature 5–10 cm deep in soil. Values are averages from three different slopes in the south (Vaseux) and north (Vernon) Okanagan during the incubation period for Gophersnakes from late June to early September 2007. We did not track hatching dates, but the average incubation period was 73–74 d at a site slightly further south (Shewchuk, 1996). The median lay date of telemetry-equipped Great Basin Gophersnakes in 2007 was June 24; thus that was the start date for these 75 d of data.
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