Bumpus in the snake den: Effects of sex, size, and body condition on mortality of red-sided garter snakes

R. Shine*, M. P. LeMaster, I. T. Moore, M. M. Olsson, R. T. Mason

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

98 Citations (Scopus)

Abstract

Huge breeding aggregations of red-sided garter snakes (Thamnophis sirtalis parietalis) at overwintering dens in Manitoba provide a unique opportunity to identify sources of mortality and to clarify factors that influence a snake's vulnerability to these factors. Comparisons of sexes, body sizes, and body condition of more than 1000 dead snakes versus live animals sampled at the same time reveal significant biases. Three primary sources of mortality were identified. Predation by crows, Corvus brachyrhynchos (590 snakes killed), was focussed mostly on small snakes of both sexes. Crows generally removed the snake's liver and left the carcass, but very small snakes were sometimes brought back to the nest. Suffocation beneath massive piles of other snakes within the den (301 dead animals) involved mostly small males and (to a lesser extent) large females; snakes in poor body condition were particularly vulnerable. Many emaciated snakes (n = 142, mostly females) also died without overt injuries, probably due to depleted energy reserves. These biases in vulnerability are readily interpretable from information on behavioral ecology of the snakes. For example, sex biases in mortality reflect differences in postemergence behavior and locomotor capacity, the greater attractiveness of larger females to males, and the high energy costs of reproduction for females.

Original languageEnglish
Pages (from-to)598-604
Number of pages7
JournalEvolution
Volume55
Issue number3
DOIs
Publication statusPublished - Mar 2001
Externally publishedYes

Keywords

  • Mating
  • Natural selection
  • Predation
  • Sexual selection
  • Size-dependent mortality

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