Frank J. Bonaccorso

Behavior of bats at wind turbines

Significance Bats are dying in unprecedented numbers at wind turbines, but causes of their susceptibility are unknown. Fatalities peak during low-wind conditions in late summer and autumn and primarily involve species that evolved to roost in trees. Common behaviors of “tree bats” might put them at risk, yet the difficulty of observing high-flying nocturnal animals has limited our understanding of their behaviors around tall structures. We used thermal surveillance cameras for, to our knowledge, the first time to observe behaviors of bats at experimentally manipulated wind turbines over several months. We discovered previously undescribed patterns in the ways bats approach and interact with turbines, suggesting behaviors that evolved at tall trees might be the reason why many bats die at wind turbines. Wind turbines are causing unprecedented numbers of bat fatalities. Many fatalities involve tree-roosting bats, but reasons for this higher susceptibility remain unknown. To better understand behaviors associated with risk, we monitored bats at three experimentally manipulated wind turbines in Indiana, United States, from July 29 to October 1, 2012, using thermal cameras and other methods. We observed bats on 993 occasions and saw many behaviors, including close approaches, flight loops and dives, hovering, and chases. Most bats altered course toward turbines during observation. Based on these new observations, we tested the hypotheses that wind speed and blade rotation speed influenced the way that bats interacted with turbines. We found that bats were detected more frequently at lower wind speeds and typically approached turbines on the leeward (downwind) side. The proportion of leeward approaches increased with wind speed when blades were prevented from turning, yet decreased when blades could turn. Bats were observed more frequently at turbines on moonlit nights. Taken together, these observations suggest that bats may orient toward turbines by sensing air currents and using vision, and that air turbulence caused by fast-moving blades creates conditions that are less attractive to bats passing in close proximity. Tree bats may respond to streams of air flowing downwind from trees at night while searching for roosts, conspecifics, and nocturnal insect prey that could accumulate in such flows. Fatalities of tree bats at turbines may be the consequence of behaviors that evolved to provide selective advantages when elicited by tall trees, but are now maladaptive when elicited by wind turbines.

ASSESSING BAT DETECTABILITY AND OCCUPANCY WITH MULTIPLE AUTOMATED ECHOLOCATION DETECTORS

Abstract Occupancy analysis and its ability to account for differential detection probabilities is important for studies in which detecting echolocation calls is used as a measure of bat occurrence and activity. We examined the feasibility of remotely acquiring bat encounter histories to estimate detection probability and occupancy. We used echolocation detectors coupled to digital recorders operating at a series of proximate sites on consecutive nights in 2 trial surveys for the Hawaiian hoary bat (Lasiurus cinereus semotus). Our results confirmed that the technique is readily amenable for use in occupancy analysis. We also conducted a simulation exercise to assess the effects of sampling effort on parameter estimation. The results indicated that the precision and bias of parameter estimation were often more influenced by the number of sites sampled than number of visits. Acceptable accuracy often was not attained until at least 15 sites or 15 visits were used to estimate detection probability and occupancy. The method has significant potential for use in monitoring trends in bat activity and in comparative studies of habitat use.

Thermal Ecology of Moustached and Ghost-Faced Bats (Mormoopidae) in Venezuela

The moustached bats, Pteronotus davyi, P. personatus , and P. parnellii , and the ghost-faced bat, Mormoops megalophylla (Mormoopidae), are homeotherms with normal to slightly low basal rates of metabolism for mammals of their body mass. They are unable to resist temperatures below 15°C for long, and none of the four species studied appears able to enter torpor. Thermal conductance of each species is high compared to expected values for mammals, but within the upper range of available values for bats. Except in P. personatus , adult females have lower basal rates of metabolism than conspecific males. We hypothesize that this sexual difference in basal rate of metabolism is related to the different thermal conditions at roost sites for each sex and that roost temperature is an important selective force in the evolution of thermoregulatory patterns and basal rate of metabolism in bats.

Plasticity of Energetics in Blossom Bats (Pteropodidae): Impact on Distribution

Blossom bats, Macroglossus minimus and Syconycteris australis , from New Guinean lowland rainforests usually enter torpor at low ambient temperatures (11–29°C). Torpid individuals maintain a 2–5°C differential of body temperature above ambient temperature. Individuals from highlands, however, regulate body temperature at 36–37°C at ambient temperatures as low as 13°C. A third species, Melonycteris melanops , exhibits imprecise temperature regulation, but rarely enters torpor. Basal rates of metabolism for lowland populations of the three species are low compared to the mammalian standard, whereas highland and subtropical S. australis and highland M. minimus have basal rates near expected values. Thermal conductances of blossom bats are lower than the mammalian standard, except in subtropical S. australis . The variation in basal rates of metabolism in nec-tarivorous bats correlates with body size and effectiveness of thermoregulation. M. minimus and S. australis have large geographic distributions, ability to cross narrow oceanic water gaps, and sufficient plasticity in energetics to meet demands imposed by environments including small oceanic islands, disturbed successional forests, and primary lowland and montane rain forests.

The Energetics of Australasian Swifts, Frogmouths, and Nightjars

Body temperature and rate of oxygen consumption were measured as a function of environmental temperature in two swiftlets from New Guinea, Collocalia esculenta and Collocalia vanikorensis, two nightjars from New Guinea, Eurostopodus mystacalis and Caprimulgus macrurus, and two frogmouths, Podargus strigoides from Australia and P. papuensis from New Guinea. Compared to rates expected from mass, basal rates of metabolism in these birds progressively decrease with an increase in mass. The reduction in basal rate may reflect food habits in swiftlets and food habits, sedentary habits, and small pectoral muscle masses in nightjars and frogmouths. The combination of small mass and low rate of metabolism might account for the variable body temperatures found in swiftlets, but no evidence of torpor has been found in these swiftlets, frogmouths, or nightjars. At cool temperatures, C. esculenta often clustered in the field and in the laboratory, a behavior that led to a 30% reduction in energy expenditure. Thermal conductances, which tend to be low in all species with low basal rates, often fell markedly in the largest frogmouth when exposed to ambient temperatures below 16° C.

HOME RANGE OF THE SOUTHERN BLOSSOM BAT, SYCONYCTERIS AUSTRALIS, IN PAPUA NEW GUINEA

Abstract Southern blossom bats, Syconycteris australis (Pteropodidae), were followed by radiotelemetry in lowland rainforest in Kau Wildlife Area, Madang Province, Papua New Guinea. Eleven individuals were monitored ≤31 days. Based on 706 radiotelemetry positions, home ranges of 11 bats were 2.7–13.6 ha. There were no significant differences in home-range sizes between sex or age classes, but there was individual overlap of the home ranges of these bats. Long axes of home ranges were 263–725 m. During each night, bats visited most parts of their home ranges; however, activity was concentrated in core-use areas representing 19–33% of the home range and containing ≥1 food patches. During the day, S. australis roosted in the foliage of trees. Bats showed fidelity to a day-roost area (0.4–10.8% of home range) but not to a single roost tree. Day-roost areas monitored within a given year showed virtually no overlap.

Rate of metabolism and temperature regulation in two small tropical insectivorous bats (peropteryx macrotis and natalus tumidirostris)

Abstract 1. 1. The rate of metabolism and temperature regulation of the small (5g) insectivorous bats Peropteryx macrotis (Emballonuridae) and Natalus tumidirostris (Natalidae) were studied. 2. 2. These bats have different basal rates of metabolism (102 vs 69% of the value predicted on the basis of body mass), thermal conductances (120 vs 92% of expected), and body temperatures during nonnothermic rest (on average 34.4 vs 32.2°C). 3. 3. Both species occasionally decrease their T b when exposed to cool temperatures. 4. 4. Thermal conditions at the roost and the availability of food and water may explain the observed BMR differences.

BASAL RATES OF METABOLISM OF NECTARIVOROUS BATS (PHYLLOSTOMIDAE) FROM A SEMIARID THORN FOREST IN VENEZUELA

The phyllostomid bats Choeroniscus godmani, Glossophaga longirostris, and Leptonycteris curasoae maintained normothermia throughout 1.5- to 3.0-h experiments at ambient temperatures of 12-290C. Above lower-critical temperatures, C. godmani and L. curasoae had basal rates of metabolism close to expected values for mammals of their body mass, but G. longirostris had a basal rate 120% of that expected. Thermal conductance for C. godmani was near the expected mass-specific value for mammals, whereas values for G. longirostris and L. curasoae were higher than expected. Poorly ventilated caves acting as heat traps were selected by L. curasoae as maternity roosts. Population size in such roosts may approach 10,000 bats, and metabolic heat production of the colony elevates air temperatures within such caves to 33-340C. Colonies of G. longirostris and C. godmani often number <20 individuals in caves, mines, or buildings with air temperatures of 26-280C. Our results support the hypothesis that ecological factors, such as roost microclimate and diet, influence rates of metabolism in phyllostomid bats.

Temperature Regulation, Rate of Metabolism, and Roost Temperature in the Greater White-Lined Bat Saccopteryx bilineata (Emballonuridae)

The thermoregulatory and metabolic responses to ambient temperature of Saccopteryx bilineata and the microclimate in three daytime roosts were studied in lowland tropical forest in Costa Rica. Between 20 and 30 C the animals usually remained normothermic (body temperature = 35.5 ± 1.2 C), and their oxygen consumption (V̇o2) was inversely related to the ambient temperature: V̇o2 (ml O2/g·h) = 12.26 − 0.35Ta (°C). The mean minimal heat transfer coefficient was 0.32 ± 0.03 ml O2/g·h·°C, which is similar to the value expected on the basis of body mass. The mean basal rate of metabolism was 1.86 ± 0.55 ml O2/g·h, or 91% of the expected rate. Air temperatures inside the tree roosts were very stable, between 25.6 and 27.5 C, while air temperature outside the trees fluctuated between 25.9 and 30.3 C. The basal rate of metabolism of S. bilineata stands in contrast to the consistently low rates (46%–64% of expected) that have been measured on other tropical insectivorous bats. This may be due to the more reliable food source that this bat selects, whereas remaining normothermic at the roost may lower predation risks and allow social interactions.

HOME RANGE AND TERRITORIALITY IN THE LEAST BLOSSOM BAT, MACROGLOSSUS MINIMUS, IN PAPUA NEW GUINEA

Abstract Least blossom bats, Macroglossus minimus (Pteropodidae), were monitored by radiotelemetry in lowland rainforest for up to 22 days in Kau Wildlife Area, Madang Province, Papua New Guinea. Based on 1,502 radiotelemetry positions, mean home range for 18 individuals was 5.8 ha ± 4.6 SD, and mean core-use area was 1.5 ± 1.3 ha. The mean long axis of the home ranges was 495 ± 258 m. Activity hotspots were associated with flowering bananas, the primary food resource of least blossom bats at Kau. During the day, M. minimus roosted singly in subcanopy or canopy foliage and showed fidelity to a day-roost area. Mean day-roost area was 0.5 ± 0.4 ha. Adult males appeared to exclude conspecifics from rich, compact feeding territories in primary forest. Overlap in home range occurred primarily in gardens and between subadults and other bats.