Ontogenetic shifts in the diet of plains hog-nosed snakes (Heterodon nasicus) revealed by stable isotope analysis

Wild snake diets are difficult to study using traditional methods, but stable isotopes offer several advantages, including integrating dietary information over time, providing data from individuals that have not fed recently, and avoiding bias towards slowly-digesting prey items. We used stable isotope signatures of carbon and nitrogen from scale tissue, red blood cells, and blood plasma to assess the diet of wild plains hog-nosed snakes (Heterodon nasicus) in Illinois. We developed Bayesian mixing models which, taken together, predicted that H. nasicus shifted from a juvenile diet predominantly (31-63%) composed of six-lined racerunners (Aspidoscelis sexlineatus) and their eggs to an adult diet predominantly (44-56%) composed of eggs of the aquatic turtles Chrysemys picta and Chelydra serpentina, with a contribution from toads (Anaxyrus sp.; 6-27%) during their adolescent years. These results agreed with sparse data from gut contents. Combining traditional and isotopic techniques for studying the diets of wild snakes can increase the utility of both types of data.

Evaluation of predator-exclusion cages used in turtle conservation: cost analysis and effects on nest environment and proxies of hatchling fitness

Context A main goal of conservation is to mitigate anthropogenic impacts on natural ecosystems, thus conservation tools themselves should not negatively affect target species. Predator-exclusion cages are effectively used to reduce predation of turtle nests; however, their effects on nest environment and developing hatchlings have not been examined. Aims Our study had the following four goals: (1) to examine effects of cages on the nest environment, (2) determine whether nest caging affects proxies for hatchling fitness, (3) evaluate whether nest predators preferentially interact with certain cage types, and (4) assess the cost-effectiveness of different nest caging designs. Methods In 2010 and 2011 in Algonquin Provincial Park, Ontario, painted turtle (Chrysemys picta; n = 93) and snapping turtle (Chelydra serpentina; n = 91) nests were assigned to one of three treatments (wooden-sided cages, above- and below-ground wire cages) or a control (no nest cage) and outfitted with a data logger to record incubation temperature. After emergence, hatching success and proxies of hatchling fitness were measured. Key results Nest temperature, hatching success, frequency of hatchling deformities and locomotor performance did not differ among cage treatments. However, hatchling body condition differed among treatments; wooden-sided and below-ground cages had the most positive influence on body condition in painted and snapping turtles, respectively. Predator interactions did not differ among treatments, and wooden-sided cages were the most inexpensive to construct. Conclusions Nest cages did not alter the nest environment from natural conditions but did alter hatchling body condition, and nest caging affected species differently. Implications Nest cages are known to reduce nest depredation, and our data indicated that, in general, nest cages also do not affect the nest environment or proxies for hatchling fitness. Thus, our findings indicated that cages are effective conservation tools that do not present secondary deleterious effects on potential recruitment.

Suitability of day-old chicks as food for captive snakes

Snakes are increasingly kept by private hobbyists and their numbers in the pet trade are increasing. Since suitable diets are essential for the health, welfare and maintenance of captive animals, objective research is required to improve and evaluate current feeding practices. Unfortunately, the husbandry of reptiles is frequently led by tradition, resulting in methods which are not evidence based. One such occurrence is the widespread belief that day-old chicks (DOCs) are unsuitable as food for captive snakes. Since this assumption has not been systematically assessed, herein I review the evidence in order to provide a more informed basis from which to evaluate the suitability of chicks in relation to rodent prey. Commonly expressed nutritional, ecological and husbandry-related concerns are examined using compilations of previously published data, new data, prior experience and nutrient compositions obtained from the Zootrition™ database. Day-old chicks were compared with two rodent species (mice and rats) since these are the most commonly used alternative prey item. Rodents were clearly the better option only in their 'naturalness', in that mammalian prey species are more frequently represented in natural diets than birds. I conclude that DOCs are a suitable prey item for snakes in captive collections since the available data provide no firm evidence for their avoidance, contrary to popular belief. Many gaps in our knowledge remain that would assist further discussion of this issue, and these are highlighted within. It is pertinent that although these data indicate that DOCs are a viable alternative to rodent prey for captive snakes, they do not necessarily indicate its superiority. In most instances, rodents and DOCs may be regarded as practically equivalent and interchangeable. It is therefore the individual keeper's preference as to which to use, informed in particular circumstances by the information presented herein.

Feeding ecology of the Great Basin Rattlesnake (Crotalus lutosus, Viperidae)

Documenting variation in organismal traits is essential to understanding the ecology of natural populations. We relied on stomach contents of preserved specimens and literature records to assess ontogenetic, intersexual, temporal, and geographic variations in the feeding ecology of the North American Great Basin Rattlesnake ( Crotalus lutosus Klauber, 1930). Snakes preyed mainly on rodents, occasionally on lizards, and less frequently on birds; squamate eggs and frogs were rarely eaten. There was a positive relationship between predator and prey size. The best predictors of this relationship were prey diameter as a function of snake body length and head size, underscoring the importance of prey diameter for gape-limited predators such as snakes. Crotalus lutosus displayed ontogenetic, sexual, and seasonal variations in diet. Smaller rattlesnakes fed predominantly on lizards, whereas larger individuals mostly fed on mammals. Females fed on lizards more often than males. The proportion of mammals in the diet was highest during the summer, a temporal variation that may be related to behavioral shifts in the diel activity and prey selectivity of C. lutosus, and (or) to differential abundance of rodents between seasons. Great Basin Rattlesnakes also displayed geographic variation in feeding habits, with snakes from the Great Basin Desert eating a higher proportion of lizards than serpents from the more northern Columbia Plateau.