Sex differences in behavior associated with reproduction often result in sex-biased mortality. Male-biased mortality appears to be the prevalent pattern for birds and mammals, but recent work suggests that higher female mortality may be the norm for snakes, at least for viviparous species. Here we used radio-telemetry to examine sex-biased mortality in Texas ratsnakes Elaphe obsoleta, an oviparous species, and test the hypothesis that differences in behavior are associated with higher rates of mortality. Female ratsnakes had lower survival than male ratsnakes. For both sexes decreased survival was associated with higher activity and increased basking. Male ratsnakes were most active and basked most during the spring when mating occurred, which was when almost all male mortality occurred. Although female ratsnakes also moved and basked most during the mating season, they maintained relatively high levels of movement and basking through the summer and fall, and female mortality occurred throughout that period. Thus, contrary to the expectation that the cost of reproduction should be highest prior to egg laying for females of oviparous snakes, the mortality pattern documented here suggests the cost of reproduction is greatest following egg laying, similar to what has been found for females of viviparous species. As capital breeders (whether oviparous or viviparous), female snakes must rebuild energy reserves following a bout of reproduction, and the associated increase in foraging and basking required to do so increases female susceptibility to predation. Further studies are required to determine if female-biased mortality is the norm in snakes and if so, to determine the demographic and life-history consequences.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics