Allen Kurta

Energetics of Pregnancy and Lactation in Freeranging Little Brown Bats (Myotis lucifugus)

We combined field measurements of metabolic rate, made with doubly labeled water, with data from our previous studies to examine reproductive energetics in 24 female little brown bats (Myotis lucifugus). Including estimates of tissue or milk production, M. lucifugus required an average of 33.7 kJ d⁻¹ of assimilated energy in pregnancy compared to 41.3 kJ d⁻¹ during lactation. Predicted insect consumption was 5.5 g d⁻¹ for a 9-gpregnant female and 6.7g d⁻¹ for a 79-g lactating female. About 2% of total energy assimilated during pregnancy was stored as new tissue, whereas lactating females exported 32% as milk. Estimated assimilated energy demand on the first day of lactation was 33.8 kJ d⁻¹ and increased to 60.3 kJ d⁻¹ at peak lactation. By subtracting laboratory measurements of roosting costs from observed metabolized energy expenditure, we calculated that foraging flight by 9-g pregnant M. lucifugus required 4.46 kJ h⁻¹; this was 13% less than allometric predictions. Foraging fight accounted for the largest proportion of the daily metabolized energy budget during pregnancy (61%) and lactation (66%). The large amount of energy devoted to foraging by this aerial-feeding bat may partially explain the low proportion of energy it allocates to tissue production and milk export.

Frequent arousal from hibernation linked to severity of infection and mortality in bats with white-nose syndrome.

White-nose syndrome (WNS), an emerging infectious disease that has killed over 5.5 million hibernating bats, is named for the causative agent, a white fungus (Geomyces destructans (Gd)) that invades the skin of torpid bats. During hibernation, arousals to warm (euthermic) body temperatures are normal but deplete fat stores. Temperature-sensitive dataloggers were attached to the backs of 504 free-ranging little brown bats (Myotis lucifugus) in hibernacula located throughout the northeastern USA. Dataloggers were retrieved at the end of the hibernation season and complete profiles of skin temperature data were available from 83 bats, which were categorized as: (1) unaffected, (2) WNS-affected but alive at time of datalogger removal, or (3) WNS-affected but found dead at time of datalogger removal. Histological confirmation of WNS severity (as indexed by degree of fungal infection) as well as confirmation of presence/absence of DNA from Gd by PCR was determined for 26 animals. We demonstrated that WNS-affected bats aroused to euthermic body temperatures more frequently than unaffected bats, likely contributing to subsequent mortality. Within the subset of WNS-affected bats that were found dead at the time of datalogger removal, the number of arousal bouts since datalogger attachment significantly predicted date of death. Additionally, the severity of cutaneous Gd infection correlated with the number of arousal episodes from torpor during hibernation. Thus, increased frequency of arousal from torpor likely contributes to WNS-associated mortality, but the question of how Gd infection induces increased arousals remains unanswered.

Energetics and Water Flux of Free-Ranging Big Brown Bats (Eptesicus fuscus) during Pregnancy and Lactation

We used doubly labeled water to measure carbon dioxide production and water flux during pregnancy and lactation in free-ranging big brown bats, Eptesicus fuscus. Mean (± SE ) carbon dioxide production was 1,749 ±144 ml/day during pregnancy ( n = 16) and 2,770 ±351 ml/day during lactation ( n = 5). Including estimates of tissue production and milk export, we calculated that the average requirement for assimilated energy was 48.9 and 105.1 kJ/day for pregnant and lactating females, respectively. About 2% of the total energy required during pregnancy was placed into fetal tissue; milk energy accounted for 28% of the energy assimilated during lactation. Daily water flux was 8.47 and 17.07 ml/day for pregnant and lactating females, respectively. We calculated that E. fuscus obtained >66% of its water preformed in the diet, but 20–22% of daily water intake was from drinking. Urinary water was the largest component of water efflux during pregnancy (72%) and lactation (56%); water exported in milk represented 22% of daily water efflux during lactation. Calculated evaporative losses for free-ranging E. fuscus were half those predicted from laboratory measurements.

Roosting Ecology of the Northern Bat (Myotis septentrionalis) and Comparisons with the Endangered Indiana Bat (Myotis sodalis)

During 1993 and 1994, we radiotracked 11 adult female and juvenile northern bats ( Myotis septentrionalis ) to 32 roost trees: 18 silver maples ( Acer saccharinum ), 1 red maple (A. rubrum ), and 13 green ashes ( Fraxinus pennsylvanica ). Fifty-three percent of the trees were living; 52% of the roosts were in crevices or hollows, and the rest were under exfoliating bark. Northern bats did not use American elms ( Ulmus americana ) in proportion to their abundance, but in general, characteristics of roost trees were similar to a random sample of apparently suitable trees. Northern bats changed roosts every 2 days, and distance between roosts varied from 6 to 2,000 m. As many as 60 adults were found in a single tree, making this the largest summer aggregation ever reported for the species. Compared with Indiana bats ( M. sodalis ) separately studied at the same site, northern bats moved greater distances between roosts and roosted more often in maples, cavities, living trees, and areas with high canopy cover.

PHILOPATRY AND MIGRATION OF BANDED INDIANA BATS (MYOTIS SODALIS) AND EFFECTS OF RADIO TRANSMITTERS

Abstract We banded 29 adult females, 2 juveniles, and 1 adult male from a maternity colony of Indiana bats (Myotis sodalis) during 1995–1998. Four banded bats were later found hibernating in caves that were separated by ≤325 km, indicating that all members of a summer colony do not hibernate or mate in the same location. We recaptured 41% of adult females (12 bats) near the initial banding site in later years, and because of this strong interannual fidelity, we recommend that resource managers reevaluate policies that allow removal of roost trees during winter. Eleven of these 12 females were radiotracked initially, but all were reproductively active and had normal body masses in subsequent years, suggesting negligible, long-term effects of the radiotracking process.

Nocturnal activity of the endangered Indiana bat (Myotis sodalis)

Acoustic monitoring and radio-tracking were used to study the nocturnal activity of adult female Indiana bats Myotis sodalis at a maternity site in Michigan, U.S.A. Pregnant bats did not use the day roost at night, but lactating females returned 2–4 times/night for 32±7 ( SE ) min/visit, presumably to feed their young. Both pregnant and lactating females night roosted as solitary individuals in trees within their foraging areas; night roosting occurred 0–6 times/night for 14±1 min each time. Bats foraged for most of the night, with the total duration of flight equalling 375±16 min/night. The bats used 13 different foraging areas that were located 0.5–4.2 km from the day roost. Bats did not fly over open fields but travelled along wooded corridors, even though such behaviour increased commuting distance by 55±11%. Current models of habitat suitability for this endangered species should be modified, taking into account the use of wooded commuting corridors and the large home range of these bats.

Diet of the Endangered Indiana Bat (Myotis sodalis) on the Northern Edge of Its Range

Abstract Dietary preferences of Indiana bats were determined by analyzing 382 fecal pellets collected beneath roost trees in southern Michigan, over parts of 3 yr. Although terrestrial insects (Lepidoptera and Coleoptera) usually dominated the diet of Indiana bats in more southern states, those in Michigan consumed mostly insects associated with aquatic environments. Indiana bats in Michigan ate primarily Trichoptera (55.1% of volume) and Diptera (25.5%), followed by Lepidoptera (14.2%) and Coleoptera (1.4%). Consumption of Diptera was highest during lactation (48.2%), whereas consumption of Lepidoptera was least during this time (7.7%). Although most insectivorous bats do not prey on mosquitoes (Culicidae), these insects were a consistent component of the diet of Indiana bats and were eaten most heavily during pregnancy (6.6%).

External insulation available to a non-nesting mammal, the little brown bat (Myotis lucifugus)

Abstract 1. 1. Cooling curves of dead little brown bats (Myotis lucifugus) were used to generate values of conductance and insulation under a variety of conditions. 2. 2. Insulation increased by 30% when the animals were placed in a wooden roost; clustering with six other bats raised insulation by 103%, but clustering within the wooden roost increased total available insulation by 258%. 3. 3. Bats on the periphery of a cluster of seven bats cooled at the same rate as animals located in the center. 4. 4. Small wooden cavities (150 and 300ml) provided 28% more total insulation to solitary bats than did a large (900ml) cavity.

Oxygen Consumption and Body Temperature of Female Little Brown Bats (Myotis lucifugus) under Simulated Roost Conditions

Oxygen consumption of freshly captured little brown bats (Myotis lucifugus) was monitored throughout the day- and night-roosting periods. The laboratory protocol simulated average roost conditions. The bats were allowed to cluster together inside a metabolic chamber made from a wooden beam; ambient temperatures were changed every 90 min and mimicked normal circadian changes measured inside an actual roost. Based on measured rates of oxygen consumption and data from the literature, daily energy expenditure of M. lucifugus in mid to late pregnancy was 32.58 kJ bat−1 day−1; energy costs during peak lactation were 49.11 kJ bat−1 day−1, or 50.7% greater than the cost of late pregnancy. There was no indication of daily torpor in pregnant, lactating, or postlactating bats; body temperature was apparently between 34 and 39 C throughout the roosting periods.

Factors Affecting the Resting and Postflight Body Temperature of Little Brown Bats, Myotis lucifugus

The body temperature (Tb) of freshly captured, adult female little brown bats (Myotis lucifugus) was investigated using two ambient temperature (Ta) regimes. Exposure Tas began with 12 C at 0600 hours and were gradually raised to either 22 or 32 C. Body temperatures were measured at 1600 hours. In general, lactating females did not attain as high a Tb as did pregnant or postlactating bats. Bats caged in clusters of seven to 12 animals had significantly greater Tbs than bats caged singly. Seasonal acclimatization over the 3-mo reproductive period was evident at the lower test Tas. The Tb of M. lucifugus appeared to be a facultative and graded response to recent environmental conditions and the effect of those conditions on the foraging success of the bats. The Tb of bats immediately after foraging flights was strongly correlated with Ta, but feeding period (first or second), date, cloud cover, and age (adult vs. juvenile) also explained some of the variation in postflight Tb.