The interrelationship between torpor expression and nest site use of western and eastern pygmy-possums (Cercartetus spp.)

Physiology and behaviour are closely linked, making knowledge of the interaction between species’ energetics and activities important when attempting to understand how animals function in the wild. I examined torpor use by western pygmy-possums (Cercartetus concinnus) and eastern pygmy-possums (C. nanus) in relation to nest site characteristics and movement patterns. In coastal mallee heath in winter, C. concinnus nested beneath leaf litter at the base of dead Banksia ornata, where they employed torpor on 69% of observed days. In warm temperate sclerophyll forest, C. nanus nested in tree hollows of Eucalyptus spp. and used torpor on 64% of days in winter and 10% in summer. Torpor was used in nest sites that were buffered from outside temperature extremes. Both species frequently reused nest sites and while C. nanus was more likely to employ torpor in a previously used site, site familiarity did not influence torpor use for C. concinnus. Additionally, C. nanus was more likely to use torpor in hollows with a higher relative thickness in both seasons. No relationship was found between range size and the number of tracking days or capture body mass, though sample sizes were small. I suggest that the thermal attributes of nest sites influence torpor use for both species and this is likely vital for maintaining a positive energy balance, stressing the importance of preserving habitat with ample potential nest sites for conservation management.

The influence of chick production on territory retention in Arctic-breeding Pacific and Yellow-billed loons

Adult birds may use the production of offspring as a measure of habitat quality when prospecting for territories, increasing competition for productive territories. We evaluated the impact of breeding success on territory retention of Pacific (Gavia pacifica) and Yellow-billed (G. adamsii) loons in the National Petroleum Reserve-Alaska on the Arctic Coastal Plain of northern Alaska using mark–resight data and multi-state modeling. We also used behavioral observations of brood-rearing adult loons to quantify the frequency of visits by prospecting loons. We hypothesized that increased competition for productive territories would result in a decrease in territory retention rates. Territory retention rates the year following successful breeding attempts were only slightly lower (0.90) than after failed breeding attempts (0.93), and few territories were consistently successful across years. Overall territory retention rates were high (0.92) and similar for both species, suggesting that adults were able to defend their territories successfully. Males had higher territory retention rates than females, but we found no influence of mass (a possible proxy for fighting ability) on territory retention. These observations, coupled with the high frequency of visits by prospecting loons, provide additional evidence that site familiarity may provide advantages to territory holders. Quantifying territory retention behaviors may also inform land management decisions for oil and gas development in areas where loons are present. High territory retention rates, frequency of visits by prospectors, and limited habitat where new territories can be established suggest that breeding habitat in northern Alaska is saturated and may be limiting Yellow-billed Loon populations. In contrast, Pacific Loons attempting to acquire a territory may be able to form new territories on smaller, unoccupied lakes.

Lizard movement tracks: variation in path re-use behaviour is consistent with a scent-marking function

Individual movement influences the spatial and social structuring of a population. Animals regularly use the same paths to move efficiently to familiar places, or to patrol and mark home ranges. We found that Australian sleepy lizards (Tiliqua rugosa), a monogamous species with stable pair-bonds, repeatedly used the same paths within their home ranges and investigated whether path re-use functions as a scent-marking behaviour, or whether it is influenced by site familiarity. Lizards can leave scent trails on the substrate when moving through the environment and have a well-developed vomeronasal system to detect and respond to those scents. Path re-use would allow sleepy lizards to concentrate scent marks along these well-used trails, advertising their presence. Hypotheses of mate attraction and mating competition predict that sleepy lizard males, which experience greater intra-sexual competition, mark more strongly. Consistent with those hypotheses, males re-used their paths more than females, and lizards that showed pairing behaviour with individuals of the opposite sex re-used paths more than unpaired lizards, particularly among females. Hinterland marking is most economic when home ranges are large and mobility is low, as is the case in the sleepy lizard. Consistent with this strategy, re-used paths were predominantly located in the inner 50% home range areas. Together, our detailed movement analyses suggest that path re-use is a scent marking behaviour in the sleepy lizard. We also investigated but found less support for alternative explanations of path re-use behaviour, such as site familiarity and spatial knowledge. Lizards established the same number of paths, and used them as often, whether they had occupied their home ranges for one or for more years. We discuss our findings in relation to maintenance of the monogamous mating system of this species, and the spatial and social structuring of the population.