Sources of Variation in Estimating Litter Characteristics of the Garter Snake, Thamnophis elegans

• Published in: Journal of herpetology 1991-09, Vol.25 (3), p.261-268
• Main Authors: Farr, Daniel R., Gregory, Patrick T.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Average linear density; Biological and medical sciences; Demecology; Eggs; Embryos; Fundamental and applied biological sciences. Psychology; Garters; Litter size; Newborns; Palpation; Parturition; Pregnancy; Reptilia. Amphibia; Snakes; Thamnophis elegans; Vertebrata
• ISSN: 0022-1511; 1937-2418
• DOI: 10.2307/1564582

Studies of snake demography usually involve the estimation of litter size and neonate size, but potential sources of variation resulting from the methods used to obtain this information are rarely considered. Using data from four populations of Thamnophis elegans, we found that estimates of litter size obtained by holding gravid snakes in captivity were less variable when dead young or undeveloped eggs were included rather than excluded; we recommend that all components of litters be reported in future studies. Litter sizes obtained by palpation of gravid snakes in the field were similar to estimates from captive births in two of three populations we examined, but not the third. There was some evidence that litters from longer-term captives were more likely to contain dead young, and, in one population, smaller young. Access to substrate heat by gravid snakes was correlated with smaller progeny in another population. In general, captive-born snakes were smaller than neonates born in the field, but some growth may have occurred in the latter. Factors that might influence the size of snakes born in captivity are temperature, feeding level of mother, and stress; in order to minimize their potential effects, we recommend that gravid snakes be held for as short a time as possible.