Mark Fitzgerald

Thermal correlates of foraging-site selection by Chinese pit-vipers (Gloydius shedaoensis, Viperidae)

1. Do thermal factors influence foraging-site selection by ectothermic predators? Snake species that obtain their prey from ambush must remain immobile for long periods, precluding overt behavioural thermoregulation; and some “ambush” snakes use thermal cues to detect endothermic prey. Plausibly, alternative ambush sites might differ either in equilibrial body temperatures available to snakes, or in the thermal “background” against which prey items must be detected. 2. We examined this topic with field data on pit-vipers (Gloydius shedaoensis) on a small island in northeastern China. Adult snakes feed only on migrating passerine birds. The snakes ambush birds both from arboreal perches (branches of small trees) and from the ground. 3. Arboreal versus terrestrial ambush sites differed both in operative temperatures and thermal “backgrounds” available to the snakes. Operative temperatures inside copper models were lower in trees than on the ground (because of wind), and snakes in arboreal ambush sites were cooler than those in terrestrial sites. Thermal backgrounds from arboreal perches were cooler (and thus, provided more contrast against prey items) than did backgrounds available from terrestrial ambush-sites. 4. Thermal factors thus modify the suitability of alternative ambush locations for these pit-vipers, but with a trade-off: a snake in a tree can “see” its prey more clearly, but may not be warm enough (and hence, able to strike fast enough) to capture it. Further work is required to determine whether or not snakes actually use such thermal differences as criteria for the selection of ambush sites.

A reluctant heliotherm: thermal ecology of the arboreal snake Hoplocephalus stephensii (Elapidae) in dense forest

Abstract Dense forests exhibit little thermal heterogeneity, and hence pose substantial difficulties for behavioral regulation of body temperatures by ectotherms. The problems are exacerbated for nocturnally active secretive taxa that spend most of their time hidden deep within shaded retreat-sites, such as our study organism Hoplocephalus stephensii in wet sclerophyll forests and rainforests of near-coastal eastern Australia. In laboratory studies these elapid snakes selected temperatures around 28°C if these levels were available within retreat-sites, but rarely basked. Body temperatures of radio-tracked snakes in the field were well below these “preferred” levels, and generally around 24°C during the active season. Nonetheless, the radio-tracked snakes consistently maintained body temperatures slightly higher than shaded air temperatures, primarily by microhabitat selection (elevated tree hollows) and occasional covert basking. The snakes exploited higher radiation levels available in the tree canopy; a snakes height in the tree was positively correlated with its body temperature. Calculated thermoregulatory indices (Am. Nat. 142 (1993) 796) confirm the low thermal quality of the habitat, and the trend for snake body temperatures to fall midway between shaded air temperatures and the animals’ set-point range. Thus, H. stephensii will bask covertly when conditions permit, but rarely do so in the field. Our study shows the potential danger of extrapolating laboratory observations of thermal preferenda to the field, and clarifies the thermal constraints influencing ectotherms in forest habitats.

Mate-guarding in free-ranging Carpet Pythons (Morelia spilota)

ABSTRACT Carpet Pythons (Morelia spilota) exhibit substantial geographic variation not only in size and colour, but also in mating systems: reproductive males in some populations battle with their rivals, whereas courting males in other locations tolerate the proximity of others. During the spring mating season (August–September) of 2017, a large male Carpet Python took up residence with a reproductive female on the roof of a house in northeastern New South Wales for at least six weeks, and was observed in intense battles with two rival males that arrived at the site. Bouts progressed from stereotyped wrestling to vigorous biting, causing severe lesions. This (apparently successful) mate defence constitutes the first report of prolonged mate-guarding behaviour in any pythonid species.