Life at the Edge: The Nesting Ecology of the World's Most Northerly Oviparous Snake and its Implications for Conservation (pp. 247-264)
Authors: (Mattias Hagman, Simon Karvemo, Johan Elmberg and Kristin Lowenborg, University of New South Wales, UK, and others)
Abstract: Temperature imposes a major constraint on reptiles in cold climates. Embryonic development is particularly challenging and oviparous (egg-laying) species may not have access to nesting sites that offer suitable thermal regimes over the duration of the incubation period. Cold-climate reptiles are therefore typically dominated by viviparous (live-bearing) species, because gravid females can regulate their internal temperature behaviorally to maintain high temperatures for the embryos developing inside their bodies. The hypothesis that ambient temperatures restrict the geographic range of oviparous reptiles is strongly supported by correlations between reproductive mode (oviparity versus viviparity) and distributional patterns. The European grass snake (Natrix natrix) is therefore unusual in that it occurs farther north and endures colder climates than any other oviparous snake species in the world. It also is unusual in preferring to nest in anthropogenic environments that function as heat sources, such as compost piles and manure heaps. Oviposition sites of these types are distinctive habitats in the sense that they provide higher temperatures than any other sites in the surrounding landscape. Our work on this system shows that the grass snake’s exploitation of these thermally distinctive man-made microhabitats enables it to colonize areas with much colder climates than can support other types of oviparous reptiles. These microhabitats also serve as a major influence on many aspects of this species life-history, including the incubation period. However, relying on man-made structures for successfully hatching the eggs is a risky strategy if circumstances suddenly change such that the structures
decrease or become inaccessible. In this chapter we review the unusual nesting ecology of the grass snake and discuss its implications for conservation.