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To cope with periods of low food availability and unsuitable environmental conditions (e.g., short photoperiod or challenging weather), many heterothermic mammals can readily go into torpor to save energy. However, torpor also entails several potential costs, and quantitative energetics can, therefore, be influenced by the individual state, such as available energy reserves. We studied the thermal energetics of brown long-eared bats (Plecotus auritus) in the northern part of its distributional range, including torpor entry, thermoregulatory ability during torpor and how they responded metabolically to an increasing ambient temperature (Ta) during arousal from torpor. Torpor entry occurred later in bats with higher body mass (Mb). During torpor, only 10 out of 21 bats increased oxygen consumption (V̇O2) to a greater extent above the mean torpor metabolic rates (TMR) when exposed to low Ta. The slope of the torpid thermoregulatory curve was shallower than that of resting metabolic rate (RMR) during normothermic conditions, indicating a higher thermal insulation during torpor. During exposure to an increasing Ta, all bats increased metabolic rate exponentially, but the bats with higher Mb aroused at a lower Ta than those with lower Mb. In bats with low Mb, arousal was postponed to an Ta above the lower critical temperature of the thermoneutral zone. Our results demonstrate that physiological traits, which are often considered fixed, can be more flexible than previously assumed and vary with individual state. Thus, future studies of thermal physiology should to a greater extent take individual state-dependent effects into account. [ABSTRACT FROM AUTHOR]

Birds providing prey with a clumped distribution often return to the previous capture site after having delivered a prey item at the nest. However, details of this foraging tactic are still poorly known, in particular for birds of prey, which often travel far from their nest. We radio-tracked four provisioning male Boreal Owls (Aegolius funereus) during the nighttime and simultaneously recorded their prey deliveries by a video camera positioned at the nest in an increase year of the vole cycle. The camera allowed prey identification and made it possible to assign prey deliveries to fixes of the foraging owls, i.e. the last recorded fix before the owl returned to the nest for a prey delivery. Within a single night, the owls returned more often than randomly expected to the area where they had captured the previous prey item. A prey item delivered was more likely than randomly expected to be of the same species as the previous prey item delivered. However, the probability of a prey item delivered being of the same species as the previous prey item delivered was independent of whether the owl had returned to the area where it captured the previous prey and did not decrease with longer time elapsed since the previous delivery. The owls did not shift hunting area from one night to the next to a larger extent than they did over a longer time span, and overall tended to shift their hunting area gradually over more nights. Our study should be replicated in a peak vole year with higher prey abundance as well as in a low vole year, which should improve the study results by enabling a higher spatial and temporal resolution of the data on the owls' movements. [ABSTRACT FROM AUTHOR]