During autumn, temperate bats must deposit fat stores for hibernation. Populations at high latitudes face four challenges: a shorter active season and shorter nights during the active season (less time to accumulate fat), a longer hibernation period (larger fat store needed), and colder nights (reduced prey availability). Mating also occurs during the prehibernation period, placing time constraints for mating and fattening on northern populations. We tested the hypothesis that these factors constrain prehibernation foraging in northern populations of little brown bats (Myotis lucifugus (Le Conte, 1831)). We measured plasma triglyceride concentration to study prehibernation fueling rates of a population near the northern range limit of the species and compared our results with previously published results from a more southern population. In contrast to bats at the lower latitude, we found consistently low concentrations of plasma triglycerides, indicating a low fuelling rate throughout the prehibernation period. However, despite an apparently low fuelling rate, bats achieved a substantially greater body mass. The discrepancy between populations suggests that environmental constraints lead northern populations to employ different behavioural or physiological strategies to prepare for hibernation.

Ebola virus is a zoonotic pathogen with a geographic range covering diverse ecosystems that are home to many potential reservoir species. Although researchers have detected Ebola virus RNA and serological evidence of previous infection in different rodents and bats, the infectious virus has not been isolated. The field is missing critical knowledge about where the virus is maintained between outbreaks, either because the virus is rarely encountered, overlooked during sampling, and/or requires specific unknown conditions that regulate viral expression. This study assessed adipose tissue as a previously overlooked tissue capable of supporting Ebola virus infection. Adipose tissue is a dynamic endocrine organ helping to regulate and coordinate homeostasis, energy metabolism, and neuroendocrine and immune functions. Through in vitro infection of human and bat (Eptesicus fuscus) brown adipose tissue cultures using wild-type Ebola virus, this study showed high levels of viral replication for 28 days with no qualitative indicators of cytopathic effects. In addition, alterations in adipocyte metabolism following long-term infection were qualitatively observed through an increase in lipid droplet number while decreasing in size, a harbinger of lipolysis or adipocyte browning. The finding that bat and human adipocytes are susceptible to Ebola virus infection has important implications for potential tissue tropisms that have not yet been investigated. Additionally, the findings suggest how the metabolism of this tissue may play a role in pathogenesis, viral transmission, and/or zoonotic spillover events.

Many mammals hibernate during winter, reducing energy expenditure via bouts of torpor. The majority of a hibernator's energy reserves are used to fuel brief, but costly, arousals from torpor. Although arousals likely serve multiple functions, an important one is to restore water stores depleted during torpor. Many hibernating bat species require high humidity, presumably to reduce torpid water loss, but big brown bats (Eptesicus fuscus) appear tolerant of a wide humidity range. We tested the hypothesis that hibernating female E. fuscus use behavioural flexibility during torpor and arousals to maintain water balance and reduce energy expenditure. We predicted: (1) E. fuscus hibernating in dry conditions would exhibit more compact huddles during torpor and drink more frequently than bats in high humidity conditions; and (2) the frequency and duration of torpor bouts and arousals, and thus total loss of body mass would not differ between bats in the two environments. We housed hibernating E. fuscus in temperature- and humidity-controlled incubators at 50% or 98% relative humidity (8°C, 110 days). Bats in the dry environment maintained a more compact huddle during torpor and drank more frequently during arousals. Bats in the two environments had a similar number of arousals, but arousal duration was shorter in the dry environment. However, total loss of body mass over hibernation did not differ between treatments, indicating that the two groups used similar amounts of energy. Our results suggest that behavioural flexibility allows hibernating E. fuscus to maintain water balance and reduce energy costs across a wide range of hibernation humidities.

In the wild, many animals generate body heat when they move which they need to get rid of to avoid overheating. Out of all the various ways that animals move, flight requires the greatest amount of energy, leading to one of the highest rates of body heat production. To lower their body temperatures, birds get rid of heat though their head, feet and the top of their wings. Losing the heat that they produce while flying is especially important for birds when considering the rapidly warming global temperatures. But how important each body area is for dissipating heat before, during and after flight has not yet been determined for any bird species. This question led Agnès Lewden and colleagues from the University of Leeds, UK and Institut Universitaire Europèen de la Mer, France to determine how yellow-collared lovebirds (Agapornis personatus) dissipate their body heat before, during and after flight.To test which body areas were important for getting rid of the excess heat the lovebirds generate while flying, the team studied seven lovebirds that were trained to fly in a wind tunnel located at the University of Leeds. The researchers randomly flew each lovebird 11 times and used a thermal camera to continuously record the lovebirds. Each recording started with the birds standing on a wooden perch before the birds flew, during flying and ended when the birds were resting again on the perch after landing. Following all flight trials, the researchers analysed the thermal videos and measured the surface temperature of the birds’ head (including the eyes and bill), the legs (including the feet), the body (including the front, back and the top of the wing), and – while the lovebirds flew – the underside of the wings (which was visible only during flight). The team then used mathematical modelling to calculate the different forms of heat loss (i.e. convection – heat loss due to air moving past the bird; radiation – heat lost to the air through infrared rays; and conduction – heat loss through physical contact) for each part of the birds before, during and after flying.Lewden and colleagues found that the birds’ heat dissipation while flying was 12-times higher than before their flight and 19-times higher than after they landed again, likely resulting from the greater amount of body heat produced during flight and their need to get rid of it. When the researchers looked at each body area separately, the team uncovered differences in how and when they dissipate heat. Specifically, before flying, body heat was mainly dissipated by the head and body but during the flight, the birds dissipated the majority of their body heat (85.9%) through the underside of the wings, despite this body area only making up 26% of the birds’ surface area. This shows the importance of the underside of the wings in keeping birds cool. The researchers also discovered that the lovebirds dissipated heat differently depending on whether they were perched or flying. The birds lost heat mainly through infrared rays (radiation) before and after their flights. However, heat loss during flight was primarily through air rushing past the underside of the wings (convection), likely reflecting the change in the lovebird's body posture during flight.Overall, Lewden and colleagues showed how lovebirds dissipate body heat through different body areas before, during and after flight. Their research is especially important when considering the rapidly warming global temperatures and suggests how other bird species may lose excess heat in hotter temperatures. Further research is needed to determine if other species cool themselves like lovebirds do before, after and on the fly.