Variation in prey resources influences the diet and behaviour of predators. When prey become limiting, predators may travel farther to find preferred food or adjust to existing local resources. When predators are habitat limited, local resource abundance impacts foraging success. We analysed the diet of Myotis lucifugus (little brown bats) from Nova Scotia (eastern Canada) to the Northwest Territories (north-western Canada). This distribution includes extremes of season length and temperature and encompasses colonies on rural monoculture farms, and in urban and unmodified areas. We recognized nearly 600 distinct species of prey, of which ≈30% could be identified using reference sequence libraries. We found a higher than expected use of lepidopterans, which comprised a range of dietary richness from ≈35% early in the summer to ≈55% by late summer. Diptera were the second largest prey group consumed, representing ≈45% of dietary diversity early in the summer. We observed extreme local dietary variability and variation among seasons and years. Based on the species of insects that were consumed, we observed that two locations support prey species with extremely low pollution and acidification tolerances, suggesting that these are areas without environmental contamination. We conclude that there is significant local population variability in little brown bat diet that is likely driven by seasonal and geographical changes in insect diversity, and that this prey may be a good indicator of environment quality.

Unlike many other mammals, bats in temperate regions employ short bouts of torpor throughout the reproductive period to maintain a positive energy balance. In addition to decreasing energy expenditure during the day, they typically alter foraging patterns as well. It is well known that various environmental conditions influence both torpor and foraging patterns, but studies of these factors often have focussed on one element in isolation thus it is not known how the two behaviours are collectively influencing temperate bats. The objective of our study was to assess how reproductive condition and environmental factors concurrently affect energy balance in female big brown bats (Eptesicus fuscus). We equipped pregnant and lactating bats in southwest Saskatchewan, Canada with temperature-sensitive radio-transmitters. While transmitters were active, skin temperature data were collected and foraging patterns were determined using triangulation. Of the various environmental and physiological parameters used to model torpor characteristics, roost type was the most important factor. Bats roosting in trees used deeper and longer torpor bouts than those roosting in buildings. Lactating bats had a tendency to forage for longer durations than pregnant bats, and often made more foraging trips. When taken together, we found that foraging duration and torpor duration were not directly related during pregnancy, but exhibited an inverse relationship during lactation. This provides support for the hypothesis that there are physiological trade-offs for reproductive bats and suggests that how bats compensate is not entirely predictable based on current environmental conditions.

Lifetime reproduction of female transgenic rat growth hormone (TRrGH) mice and their normal siblings was evaluated on a high-protein (38%) diet, a standard diet (23% protein), and the standard diet supplemented with sucrose cubes. Compared with those on the standard diet, normal mice fed the high-protein diet showed significant increases in litter size, number of litters, and lifetime fecundity. Number of litters and lifetime fecundity were also enhanced in normal mice fed sucrose. TRrGH mice showed no significant improvements in reproduction on the high-protein diet, but they were significantly smaller. Sucrose dramatically improved reproduction of TRrGH mice, with no reduction in mature mass. The percentage of fertile TRrGH mice increased from 45% on standard chow to 71% with sucrose. The number and size of litters of TRrGH mice also significantly increased with sucrose, mean lifetime fecundity doubling from 9 pups on standard food to 18 pups on sucrose. However, TRrGH mice did not attain the reproductive success of normal mice on any diet. These results suggest that TRrGH mice are energetically stressed by enforced channelling of energy into growth. An immense literature addresses infertility due to energy limitation and stress generally. We synthesize these aspects with growth hormone transgenesis to derive an integrated view of neuroendocrine energy regulation relevant to restoring fertility of transgenic GH animals.

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