Virgil Brack

Energy availability influences microclimate selection of hibernating bats.

SUMMARY Many species hibernate to conserve energy during periods of low food and water availability. It has long been assumed that the optimal hibernation strategy involves long, deep bouts of torpor that minimize energy expenditure. However, hibernation has ecological (e.g. decreased predator avoidance) and physiological (e.g. sleep deprivation) costs that must be balanced with energy savings; therefore, individuals possessing sufficient energy reserves may reduce their use of deep torpor. We tested the hypothesis that energy (fat) availability influences temperature selection of two fat-storing bat species during hibernation. We predicted that individuals with small energy reserves would select colder temperatures for hibernation in order to minimize energy expenditure, while individuals with larger energy reserves would choose warmer temperatures to minimize the costs of hibernation. Results from our field experiment indicate that little brown myotis (Myotis lucifugus) hibernating in warm microclimates were significantly heavier than individuals hibernating in cooler microclimates. To determine if energy availability was mediating this relationship, we limited fatty acid availability with mercaptoacetate (MA) and quantified its effect on torpid metabolic rate (TMR) and thermal preference of big brown bats (Eptesicus fuscus). Administration of MA caused a 43% drop in TMR at 10°C and caused bats to choose significantly colder temperatures for hibernation. Our results suggest that fat-storing bats minimize torpor expression using both physiological and behavioral mechanisms.

MODELING SURVIVAL RATES OF HIBERNATING MAMMALS WITH INDIVIDUAL-BASED MODELS OF ENERGY EXPENDITURE

Abstract Estimating survival rates of naturally hibernating mammals is important for ecological and conservation reasons, but empirical estimates are logistically difficult to obtain. Individual-based models can estimate survival under circumstances that would be impossible or unethical to test experimentally. Here, we present an individual-based model based on energy expenditure to estimate survival rates of hibernating little brown bats (Myotis lucifugus). Initial simulations assumed only thermal energetics of individuals were important to energy expenditure; subsequent simulations assumed bats also use a behavioral mechanism (clustering) to reduce energy expenditure during euthermy. Our model suggests that survival rates are high (>0.96) for populations that cluster during hibernation and experience no human disturbance, regardless of winter length (between 90 and 200 d). Survival rates are much lower, especially at long winter lengths (0.73 ± 0.01 SD at 200 d), if bats do not cluster. Human disturbances strongly affect survival rates, but the relationship is not linear. Survival rates are not lowered substantially by a limited number of disturbances because those arousals would have occurred naturally, but as disturbances reach a frequency threshold (dependent on winter length and disturbance pattern) they become very detrimental to survival. Thus, our model has implications for understanding the effect of environmental variability, social thermoregulation, and human disturbance on mammals hibernating under natural conditions.

Capture and Reproductive Trends in Summer Bat Communities in West Virginia: Assessing the Impact of White-Nose Syndrome

Abstract Although it has been widely documented that populations of cave-roosting bats rapidly decline following the arrival of white-nose syndrome (WNS), longer term reproductive effects are less well-known and essentially unexplored at the community scale. In West Virginia, WNS was first detected in the eastern portion of the state in 2009 and winter mortality was documented in 2009 and 2010. However, quantitative impacts on summer bat communities remained unknown. We compared “historical” (pre-WNS) capture records and reproductive rates from 11,734 bats captured during summer (15 May to 15 August) of 1997–2008 and 1,304 captures during 2010. We predicted that capture rates (number of individuals captured/net-night) would decrease in 2010. We also expected the energetic strain of WNS would cause delayed or reduced reproduction, as denoted by a greater proportion of pregnant or lactating females later in the summer and a lower relative proportion of juvenile captures in the mid–late summer. We found a dr...

WHITE-NOSE SYNDROME AND WING DAMAGE INDEX SCORES AMONG SUMMER BATS IN THE NORTHEASTERN UNITED STATES

White-nose syndrome (WNS) adversely affects millions of bats hibernating in caves of the eastern United States. Beginning in 2009, the US Fish and Wildlife Service supported use of a wing damage index (WDI) scoring system (scale of 0 to 3, or no damage to severe) to assess wing damage of bats captured during summer. Based on bat captures at 459 mist net sites in Pennsylvania, New York, Maryland, Virginia, and New Jersey, USA, we questioned whether WDI scores varied by species group, date, and distance to the closest known affected hibernaculum. We also compared relative health (body mass index [BMI] scores) to WDI scores. Of 3,419 bats (nine species), only four individuals (0.1%; little brown [Myotis lucifugus] and northern bats [Myotis septentrionalis]) were scored as a 3 and 47 (1.4%; big brown [Eptesicus fuscus], little brown, and northern bats) as a 2. All tree bats (eastern red [Lasiurus borealis], hoary [Lasiurus cinereus], and silver-haired bats [Lasionycteris noctivagans]) scored a 0 or 1, suggesting that these species were not affected by WNS. The average WDI score decreased as summer progressed, although trends were weak. Average WDI score and number of bats with class 2 and 3 damage increased with proximity to a known WNS-positive hibernaculum. Similarly, the number of bats with severe wing damage (scoring 2 or 3) was greater at sites closer to infected hibernacula, but little variance was explained by the trend. When species-specific BMI was examined, trends were consistent by sex (female BMI scores were higher than those of males), but no relationship was discovered between BMI and WDI scores. We conclude that, at this larger geographic scale, WDI is not a clear indicator of bat health.

DIET OF THE GRAY MYOTIS (MYOTIS GRISESCENS): VARIABILITY AND CONSISTENCY, OPPORTUNISM, AND SELECTIVITY

Abstract Food habits of the endangered gray myotis (Myotis grisescens) were ascertained from 10,736 fecal pellets collected from 1,225 bats of known sex, age, reproductive condition, and capture locations, including 5 maternity caves and 2 dispersal caves in Missouri. Diets were compared to availability of insects in 80 light-trap samples collected concomitantly with fecal samples. Proportional availability of insects varied among locations, over the season, between seasons, and between early-evening and late-night samples. Similarly, the diet varied among locations, over time, between early and late samples, and among sample groups by sex, age, and reproductive condition. Trichopterans, coleopterans, and lepidopterans were important in the diet and in light-trap samples, but there was poor correlation between corresponding diet and light-trap samples. Plecopterans, ephemeropterans, and dipterans were occasionally common in light-trap and dietary samples, although again there was poor correlation between corresponding diet and light-trap samples. Gray myotis forage individually over long distances along streams and wooded riparian habitats. Although this habitat produces a characteristic assemblage of insect prey, proportional availability varies temporally and spatially. Thus, although specific diet samples do not match corresponding insect samples, on a broader scale, diets and insect availability do correspond. On a microscale, the gray myotis exhibited some characteristics of an opportunistic forager, feeding on readily available prey, but on a macroscale was selective, feeding in aquatic-based habitats where specific types of insect prey were abundant. Juveniles foraged more in woodlands and ate more coleopterans, which may provide a greater energy reward per unit of capture effort, than did adults. Conservation efforts should include both aquatic and wooded riparian habitats.

Bats of the Cumberland Plateau and Ridge and Valley Provinces, Virginia

Abstract The distribution and abundance of bats in western Virginia are poorly documented, especially in summer. Herein, we report results for captures of bats during 8 summers (between 2000 and 2009) of mist-netting surveys in the Cumberland Plateau and the Ridge and Valley provinces of Virginia. We captured 1575 bats representing 11 species and report multiple new county records for 10 of the 11 counties surveyed. Average capture rate was 1.9 bats per net-night, and Simpsons diversity index was 3.9 for the 8-year period. We also documented earliest and latest detection dates for reproducing females and presence of juveniles in 7 bat species. Our data contribute to an understanding of the relative abundance, distribution, and reproductive phenology of bats in these provinces, and may aid in the development of sound conservation strategies for these species in Virginia and surrounding states. Baseline data like these are increasingly important in light of White-Nose Syndromes effects on bat populations in the region.

Indexing at Different Scales: A response to Reichard et al.

Since 2009, resource management agencies throughout much of the United States have required biologists to record a wing damage index (WDI) for bats captured. Interestingly, this requirement preceded publication of the technique (Reichard and Kunz, 2009), which (when published) advocated WDI as an ‘‘important tool for assessing the spread of [white-nose syndrome, or WNS] and for establishing baseline data for unaffected bats.’’ This statement immediately found a willing audience among regulatory biologists who saw WDI scores as a potential, easy proxy for monitoring the extent of WNS across broad geographic regions. In summer 2009, we surveyed bats at 459 sites in New York, Pennsylvania, New Jersey, Virginia, and Maryland and, as required, collected WDI scores for each bat captured (Francl et al., 2011). Like many biologists, we expected to document numerous bats with severely necrotic wings. Only 4 of 3,419 bats had severe (WDI53) and 47 had moderate (WDI52) damage. Taken alone, this result indicates that either WDI did not provide the easy assessment of the occurrence and severity of WNS across the landscape for which the regulatory community had hoped or that the majority of bats we captured were healthy. In an effort to further understand the value of the WDI, we attempted to correlate WDI with body mass index (BMI), a surrogate for health in bats, and with distance from infected hibernacula. In their response, Reichard et al. (2011) correctly questioned whether we failed to find a relationship between BMI and WDI scores because our sample included bats of multiple species and bats that were heavier due to full stomachs or pregnancy. The effect of a full stomach or pregnancy might be addressed with larger sample sizes, but our data set is the largest of which we are aware. Even when we accounted for these potential interand intraspecific biases, we found no apparent patterns between BMI and WDI. This is not surprising given that Reichard and Kunz (2009) only found such effects for bats with severe wing damage, which were extremely rare in our samples. This rarity perhaps is because these bats die or do not travel far from the roost. We did, however document higher WDI scores close to infected hibernacula. To some extent, Francl et al. (2011) was obsolete before it was published. Much like Reichard and Kunz (2009), we made our results available to other biologists prior to publication. Partly in response to this effort, WDI is now used by resource agencies to identify bats that should be subjected to more invasive and expensive analyses such as genetic testing (Lorch et al., 2010) for the putative causal organism (Geomyces destructans) or histology to confirm infection (Meteyer et al., 2009). Our comments about utility of WDI only apply to its use as a proxy for studying large-scale incidence of WNS, and thus do not preclude its use in a more controlled setting or its value as part of a suite of measurements.