Search

In many species of snakes, particularly viperids from temperate regions, production of offspring by individuals occurs on a less-than-annual schedule. Accordingly, acquiring sufficient energy and nutrient reserves for reproduction in females often requires more than a single active season. This is termed capital mode. Yet, in some instances, annual reproduction occurs under conditions where foraging success is high and environmental factors are compliant. This is termed income mode. Here, we addressed the hypothesis of annual versus less-than-annual reproduction from a long-term radio-telemetric study involving female western diamond-backed rattlesnakes Crotalus atrox from a population of the Sonoran Desert in Arizona. From 2001 to 2008, 16 of 20 radio-telemetered females produced 36 litters, which 32 were informative in addressing the hypothesis of reproductive frequency. In 14 females, litters were produced on a biennial or at-least-biennial (≥biennial) cycle. However, seven females demonstrated annual reproduction, of which several had previously reproduced on a biennial or greater cycle. Because our study was non-experimental, we were unable to unambiguously identify specific proximate factors that contributed to the shift in annual reproduction. Nonetheless, we established that greater annual rainfall was significantly correlated with shifts to annual reproduction. Based on other studies, we hypothesize that increased rainfall was causally linked with increases in rodent densities and the foraging success of female C. atrox, which in turn is linked to reproduction. We describe, moreover, several characteristics of female C. atrox that appear to facilitate the potential for annual reproduction. In long-lived species, such as C. atrox, our research underscores the necessity to follow individuals for extended periods to gain insights on reproductive cycles not captured by point sampling methods, such as short-term field studies or reliance on museum specimens. [ABSTRACT FROM AUTHOR]

Information on behavioural and physiological processes of newborn reptiles is often difficult to obtain under natural conditions, especially in lizards and snakes. Consequently, we lack information on a wide range of biological phenomena (e.g. thermoregulation, digestion, circadian activity rhythms) in neonates of these taxa. Here, we report novel behaviour in newborn sibling sidewinder rattlesnakes Crotalus cerastes, a desert-inhabiting species of south-western North America. At the entrances of their natal burrows, neonates formed aggregations (‘balls’) during daylight hours, which involved frequent movements of individuals within these balls. Through the study of two radio-telemetered females and their litters ( n=20 offspring), we obtained temperature data from the mothers, centre of the snake balls, and from multiple sites in the immediate environment for 10 days post-birth, the period that is coincident with maternal attendance and the first cycle of ecdysis. The core temperatures of the snake balls showed significant stability over the extreme thermal ranges of the environment. Although other functions are possible, such as those related to water conservation and antipredator defence, we suggest that frequent movements of individuals within the balls involved selection of a thermal optimum to enhance ecdysis. Based on other studies of aggregation in animals, dynamic aggregative behaviour in newborn sibling C. cerastes implicates self-assembly and suggests that individuals benefit from behavioural interactions with their siblings. One plausible scenario for the evolution of this type of dynamic aggregation involves thermal selection among sibling neonates for optimal basking sites within natal refugia in extreme environments such as desert landscapes. Moreover, it is possibly limited to species of vipers (and other snakes) that are viviparous and where maternal care is present up to the time of shedding in neonates. [ABSTRACT FROM AUTHOR]