Wildlife conservation in multi-use landscapes requires identifying and conserving critical resources that may otherwise be destroyed or degraded by human activity. Summer day-roost sites are critical resources for bats, so conserving roost sites is thus a focus of many bat conservation plans. Studies quantifying day-roost characteristics typically focus on female bats due to their relative importance for reproduction, but large areas of species’ ranges can be occupied predominantly by male bats due to sexual segregation. We used VHF telemetry to identify and characterize summer day-roost selection by male northern long-eared bats (Myotis septentrionalis) in a ponderosa pine (Pinus ponderosa) forest in South Dakota, USA. We tracked 18 bats to 43 tree roosts and used an information theoretic approach to determine the relative importance of tree- and plot-level characteristics on roost site selection. Bats selected roost trees that were larger in diameter, more decayed, and under denser canopy than other trees available on the landscape. Much like studies of female northern long-eared bats have shown, protecting large-diameter snags within intact forest is important for the conservation of male northern longeared bats. Unlike female-specific studies, however, many roosts in our study (39.5%) were located in short (≤ 3 m) snags. Protecting short snags may be a low-risk, high-reward strategy for conservation of resources important to male northern long-eared bats. Other tree-roosting bat species in fire-prone forests are likely to benefit from forest management practices that promote these tree characteristics, particularly in high-elevation areas where populations largely consist of males.
Homeothermy requires increased metabolic rates as temperatures decline below the thermoneutral zone, so homeotherms typically select microhabitats within or near their thermoneutral zones during periods of inactivity. However, many mammals and birds are heterotherms that relax internal controls on body temperature and go into torpor when maintaining a high, stable body temperature, which is energetically costly. Such heterotherms should be less tied to microhabitats near their thermoneutral zones and, because heterotherms spend more time in torpor and expend less energy at colder temperatures, heterotherms may even select microhabitats in which temperatures are well below their thermoneutral zones. We studied how temperature and daily torpor influence the selection of microhabitats (i.e., diurnal roosts) by a heterothermic bat (Myotis thysanodes). We (1) quantified the relationship between ambient temperature and daily duration of torpor, (2) simulated daily energy expenditure over a range of microhabitat temperatures, and (3) quantified the influence of microhabitat temperature on microhabitat selection. In addition, warm microhabitats substantially reduced the energy expenditure of simulated homeothermic bats, and heterothermic bats modulated their use of daily torpor to maintain a constant level of energy expenditure across microhabitats of different temperatures. Daily torpor expanded the range of energetically economical microhabitats, such that microhabitat selection was independent of microhabitat temperature. Our work adds to a growing literature documenting the functions of torpor beyond its historical conceptualization as a last‐resort measure to save energy during periods of extended or acute energetic stress.
Wildlife conservation in multi-use landscapes requires identifying and conserving critical resources that may otherwise be destroyed or degraded by human activity. Summer dayroost sites are critical resources for bats, so conserving roost sites is thus a focus of many bat conservation plans. Studies quantifying day-roost characteristics typically focus on female bats due to their relative importance for reproduction, but large areas of species' ranges can be occupied predominantly by male bats due to sexual segregation. We used VHF telemetry to identify and characterize summer day-roost selection by male northern long-eared bats (Myotis septentrionalis) in a ponderosa pine (Pinus ponderosa) forest in South Dakota, USA. We tracked 18 bats to 43 tree roosts and used an information theoretic approach to determine the relative importance of tree-and plot-level characteristics on roost site selection. Bats selected roost trees that were larger in diameter, more decayed, and under denser canopy than other trees available on the landscape. Much like studies of female northern long-eared bats have shown, protecting large-diameter snags within intact forest is important for the conservation of male northern longeared bats. Unlike female-specific studies, however, many roosts in our study (39.5%) were located in short (≤ 3 m) snags. Protecting short snags may be a low-risk, high-reward strategy for conservation of resources important to male northern long-eared bats. Other tree-roosting bat species in fire-prone forests are likely to benefit from forest management practices that promote these tree characteristics, particularly in high-elevation areas where populations largely consist of males.
Many animals employ heterothermy to conserve energy during periods of inactivity, stress, or low resource availability. Unlike homeotherms, these heterotherms have some flexibility in body temperature. Unlike poikilotherms, heterotherms can maintain body temperatures independently from their environments. Heterotherms should thus exhibit fundamentally different responses to suboptimal environmental temperatures than either homeotherms or poikilotherms. In a species of heterothermic bat (Myotis thysanodes), we studied how daily torpor and roost selection could mitigate the energetic consequences of variation in ambient temperature. We then (1) quantified the relationship between ambient temperature and torpor use, (2) simulated daily energy expenditure over a range of roost temperatures, and (3) quantified the influence of roost temperature on roost selection. Bats did not select roosts with specific thermal characteristics, nor did ambient temperature alter patterns of roost selection. This was likely because bats could modulate use of torpor to maintain a consistent level of energy expenditure over the course of a day, irrespective of ambient temperature. Thermoregulatory processes in heterotherms differ from that of homeotherms and poikilotherms, including through behaviours as universal as habitat selection. Unlike homeotherms, bats face little pressure to select warm habitats to avoid heat loss during periods of inactivity--bats can use daily torpor to fully offset any increases in energy expenditure from maintaining homeothermy at colder temperatures.
Ecological research is critical for informing management of at-risk species, for example, by identifying what drives occupancy of species across landscapes. However, restricting research to public land and omitting private land, as commonly occurs in ecological research, can bias inferences because important drivers of population and community patterns may vary with land ownership. We conducted a landscape-scale study of a species of conservation concern, white-tailed prairie dog (WTPD; Cynomys leucurus), across multiple land ownerships in Wyoming. We quantified how WTPD occupancy varied with both land ownership and biotic and abiotic factors. We established a baseline occupancy rate for WTPD in Wyoming, and quantified how this baseline would have been biased if we had restricted our study to public land. We surveyed 440 sites throughout the Wyoming range of WTPD, which included sites on public (275), private (80), checkerboard (55), and Wind River Indian Reservation (30) land. We found that WTPD occupancy varied significantly with land ownership and elevation, with WTPD being four times as likely to occupy private as public land at the median study area elevation. This difference in occupancy may have been driven by variation in habitat quality between ownership types, but we could not definitively determine the underlying cause. Regardless of land ownership, WTPD occupancy increased with bare ground, but also when recent plant biomass (as estimated by NDVI) was higher than a site's long-term average biomass. In other words, WTPD tended to occupy sparsely vegetated sites, but occupancy increased with short-term increases in biomass. The strong land ownership effect illustrates how study area delineation in relation to land ownership can influence research inferences and management actions, and why it is counterproductive to presuppose that certain land ownerships contain low-quality habitat. Ecologically, the variation in occupancy resulting from long-term site conditions, such as overall density of vegetation, relative to short-term site conditions, such as changes in plant biomass, can be used to improve long-term population monitoring for WTPD.
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