Reproductive frequency and size-dependence of fecundity in the Giant Gartersnake (Thamnophis gigas)

Herpetological Conservation and Biology
By: , and 



How reproductive output changes with age or size is a key life-history trait that can affect which demographic rates most influence population growth. Although many studies have investigated the reproductive ecology of gartersnakes, we know little about reproduction in the threatened Giant Gartersnake, Thamnophis gigas. We used X-radiography to determine reproductive status and estimated fecundity for 73 female T. gigas collected from several regions within the range of this species in the Sacramento Valley of California, USA, and synthesize these data with data from litters born in captivity to improve our understanding of reproduction in this species. Average total litter size determined from X-rays (15.9) and captive-born litters (15.5) are within the ranges reported from other gartersnakes, but captive-born litters had high rates of stillbirth. Only 154 of 202 neonates from captive snakes were born alive, and seven of 13 litters contained at least one stillborn neonate. We found that fecundity was positively related to maternal snout-vent length, and some evidence that larger litters contained smaller neonates. The proportion of X-rayed females that were gravid was 0.50 in 2014, 0.47 in and 2015, and 0.64 in 2016. Central California experienced an exceptional drought from 2012–2015, which may have affected the reproductive output and frequency of T.  gigas. Our estimates of reproductive frequency and size-dependent fecundity in T. gigas provide valuable information that can be used in demographic models of this threatened species. Our results demonstrate that X-radiography is a useful, minimally invasive means to study fecundity in wild populations of snakes.

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Publication type Article
Publication Subtype Journal Article
Title Reproductive frequency and size-dependence of fecundity in the Giant Gartersnake (Thamnophis gigas)
Series title Herpetological Conservation and Biology
Volume 13
Issue 1
Year Published 2018
Language English
Publisher Herpetological Conservation and Biology
Contributing office(s) Western Ecological Research Center
Description 11 p.
First page 80
Last page 90
Country United States
State California
Other Geospatial Sacramento Valley
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