Robert M. R. Barclay

Population Structure of Temperate Zone Insectivorous Bats in Relation to Foraging Behaviour and Energy Demand

(1) The morphology, echolocation calls, foraging behaviour and prey distribution of two temperate zone species of insectivorous bats was studied to assess the hypothesis that sexual differences in distribution pattern are the result of differences in energy demand. (2) In an area of the eastern slopes of the Rocky Mountains (Canada) characterized by low ambient temperatures and low insect abundance, over 90%yo of the Myotis lucifugus caught during the summer were adult males while an equal sex ratio of Myotis evotis was caught. (3) M. lucifugus forage low over water on aerial prey, especially chironomids, which are abundant only for a short time after sunset. (4) M. evotis forage along paths and in forest and prey primarily on moths. They take insects from the air but laboratory studies indicate that they are also adept at gleaning prey from the ground and vegetation. This provides a broader, more predictable food resource than is available to M. lucifugus. (5) I suggest that the flexible foraging strategy of M. evotis allows reproductive females, with their high energy demand, to inhabit areas that cannot support reproductive female M. lucifugus. Males of both species can exist in such areas because of lower energy demand and, potentially, the use of torpor under adverse conditions. Selecting such areas and reducing foraging time may benefit males if there are risks incurred while they forage.

Prey detection, dietary niche breadth, and body size in bats : why are aerial insectivorous bats so small?

Dietary niche breadth increases with body size for most predators such as invertebrates (e.g., Zaret 1980), fish (Werner 1974), mammals (Rosenzweig 1968), and birds (Ashmole 1968), including aerial insectivorous birds (Hespenheide 1971). Essentially, large animals can detect, capture, and consume both small and large prey, whereas smaller predators are limited to small prey. For bats that catch flying insects, we argue that the above generalization does not hold because the prey detection system of aerial insectivorous bats renders small prey unavailable to larger bats. We suggest that this limitation has also constrained the evolution of large aerial insectivorous bats. Aerial insectivorous bats are small. The mean body mass of these bats in three faunas that we analyzed is between 10 and 15 g, and most species have body masses under 10 g (North America, n 28, X + SD = 12.8 + 11.7 g; Central America, n = 22, X = 10.1 + 8.2 g; southern Africa, n = 28, X 15.1 + 10.6 g; see also figs. 1, 2 and Appendix). Similar observations for other areas have been made by McNab (1969), Black (1974), Fenton and Fleming (1976), and Krzanowski (1977). Several hypotheses could explain the small size of aerial insectivorous bats. First, aerial insectivorous animals in general may be small because of constraints imposed by flight (Norberg 1986; Norberg and Rayner 1987). Second, prey size may limit the size of aerial insectivorous animals (e.g., McNab 1969; Black 1974). Bats eat small insects, which may be energetically inadequate for large flying predators. Finally, bat size may be limited by phylogenetic onstraints. Comparisons of the body mass of aerial insectivorous bats with that of aerial insectivorous birds, insectivorous bats that take their prey from surfaces (gleaners), and noninsectivorous bats do not support any of these hypotheses. In North America, aerial insectivorous bats are significantly lighter than diurnal or nocturnal aerial insectivorous birds (fig. 1; Kruskal-Wallis test, H = 33.8, n = 77, P < .001; multiple comparisons [Zar 1984], bats vs. diurnal birds, Q = 4.16, P < .001; bats vs. nocturnal birds, Q = 5.27, P < .001). Sixteen of 28 (57.1%) bat species weigh less than 10 g, whereas only 2 of 42 (4.8%) diurnal aerial insectivorous bird species are this small. None of the seven nocturnal aerial insectivorous bird species weighs less than 48 g. Thus, aerial insectivorous bats are smaller than expected from aerodynamic restrictions alone. Furthermore, feeding aerially on insects per se does not necessitate the small body size that is

Variation in bat and bird fatalities at wind energy facilities: assessing the effects of rotor size and tower height

Wind energy is a rapidly growing sector of the alternative energy industry in North America, and larger, more productive turbines are being installed. However, there are concerns regarding bird and bat fatalities at wind turbines. To assess the influence of turbine size on bird and bat fatalities, we analyzed data from North American wind energy facilities. Diameter of the turbine rotor did not influence the rate of bird or bat fatality. The height of the turbine tower had no effect on bird fatalities per turbine, but bat fatalities increased exponentially with tower height. This suggests that migrating bats fly at lower altitudes than nocturnally migrating birds and that newer, larger turbines are reaching that airspace. Minimizing tower height may help minimize bat fatalities. In addition, while replacing older, smaller turbines with fewer larger ones may reduce bird fatalities per megawatt, it may result in increased numbers of bat fatalities.

Barotrauma is a significant cause of bat fatalities at wind turbines

Summary Bird fatalities at some wind energy facilities around the world have been documented for decades, but the issue of bat fatalities at such facilities — primarily involving migratory species during autumn migration — has been raised relatively recently [1,2]. Given that echolocating bats detect moving objects better than stationary ones [3], their relatively high fatality rate is perplexing, and numerous explanations have been proposed [1]. The decompression hypothesis proposes that bats are killed by barotrauma caused by rapid air-pressure reduction near moving turbine blades [1,4,5]. Barotrauma involves tissue damage to air-containing structures caused by rapid or excessive pressure change; pulmonary barotrauma is lung damage due to expansion of air in the lungs that is not accommodated by exhalation. We report here the first evidence that barotrauma is the cause of death in a high proportion of bats found at wind energy facilities. We found that 90% of bat fatalities involved internal haemorrhaging consistent with barotrauma, and that direct contact with turbine blades only accounted for about half of the fatalities. Air pressure change at turbine blades is an undetectable hazard and helps explain high bat fatality rates. We suggest that one reason why there are fewer bird than bat fatalities is that the unique respiratory anatomy of birds is less susceptible to barotrauma than that of mammals.

Constraints on Reproduction by Flying Vertebrates: Energy and Calcium

Among mammals, many life-history traits correlate with body size (Millar 1977, 1981; Wooton 1987; Harvey and Read 1988; Read and Harvey 1989). In general, large mammals live long lives during which they produce litters of few, large, slow-growing, late-maturing offspring. Small mammals live short lives and have litters of many, small, rapidly growing, early-maturing offspring. Even when body size is factored out, however, life-history traits correlate with one another (Read and Harvey 1989). Some mammals produce litters of few, large, slow-growing offspring and live long lives for their body size, whereas others produce large litters of fast-growing young and die at an early age. In the debate over the evolution of mammalian life-history variation, the second largest group of mammals, bats, has been either completely ignored (Sacher and Staffeldt 1974; Western 1979; Millar 1981; Western and Ssemakula 1982) or severely underrepresented (Millar 1977; Blueweiss et al. 1978; Wooton 1987; Promislow and Harvey 1990). Bats can be used to argue against a simple allometric constraint on life-history variation. Despite their small size (most have body masses under 100 g; Barclay and Brigham 1991), bats are long-lived (Tuttle and Stevenson 1982) and have uniformly small litters. Most species produce only a single young, and only eight are known to regularly produce more than two young (Tuttle and Stevenson 1982). The purpose of this note is to propose a physiological nd evolutionary explanation for the consistently small litter size of bats. I show that bats invest more per young than do other mammals and hypothesize that this results from a fundamental, proximate constraint acting on flying vertebrates in general that restricts the number of offspring they can raise at one time. Although such costs of reproduction are typically measured in terms of energy, I suggest hat calcium for offspring skeletal growth is a more critical constraint. Finally, I propose that birds and bats are influenced to different degrees by this constraint because of basic differences in their parental care systems and foraging abilities. One hypothesis for why bats have small itters is that flight constrains reproductive output. Litter mass may be constrained, which limits the number of viable neonates that can be produced (Millar 1977). The mass of a near-term litter influ-

Causes of bat fatalities at wind turbines: hypotheses and predictions.

Abstract Thousands of industrial-scale wind turbines are being built across the world each year to meet the growing demand for sustainable energy. Bats of certain species are dying at wind turbines in unprecedented numbers. Species of bats consistently affected by turbines tend to be those that rely on trees as roosts and most migrate long distances. Although considerable progress has been made in recent years toward better understanding the problem, the causes of bat fatalities at turbines remain unclear. In this synthesis, we review hypothesized causes of bat fatalities at turbines. Hypotheses of cause fall into 2 general categories—proximate and ultimate. Proximate causes explain the direct means by which bats die at turbines and include collision with towers and rotating blades, and barotrauma. Ultimate causes explain why bats come close to turbines and include 3 general types: random collisions, coincidental collisions, and collisions that result from attraction of bats to turbines. The random collision hypothesis posits that interactions between bats and turbines are random events and that fatalities are representative of the bats present at a site. Coincidental hypotheses posit that certain aspects of bat distribution or behavior put them at risk of collision and include aggregation during migration and seasonal increases in flight activity associated with feeding or mating. A surprising number of attraction hypotheses suggest that bats might be attracted to turbines out of curiosity, misperception, or as potential feeding, roosting, flocking, and mating opportunities. Identifying, prioritizing, and testing hypothesized causes of bat collisions with wind turbines are vital steps toward developing practical solutions to the problem.

Genetic analysis reveals demographic fragmentation of grizzly bears yielding vulnerably small populations

Ecosystem conservation requires the presence of native carnivores, yet in North America, the distributions of many larger carnivores have contracted. Large carnivores live at low densities and require large areas to thrive at the population level. Therefore, if human-dominated landscapes fragment remaining carnivore populations, small and demographically vulnerable populations may result. Grizzly bear range contraction in the conterminous USA has left four fragmented populations, three of which remain along the Canada–USA border. A tenet of grizzly bear conservation is that the viability of these populations requires demographic linkage (i.e. inter-population movement of both sexes) to Canadian bears. Using individual-based genetic analysis, our results suggest this demographic connection has been severed across their entire range in southern Canada by a highway and associated settlements, limiting female and reducing male movement. Two resulting populations are vulnerably small (≤100 animals) and one of these is completely isolated. Our results suggest that these trans-border bear populations may be more threatened than previously thought and that conservation efforts must expand to include international connectivity management. They also demonstrate the ability of genetic analysis to detect gender-specific demographic population fragmentation in recently disturbed systems, a traditionally intractable yet increasingly important ecological measurement worldwide.

The effect of reproductive condition on the foraging behavior of female hoary bats, Lasiurus cinereus

SummaryFemale mammals experience larg changes in time and energy budgets associated with reproduction and these may influence the foraging strategies of individuals. I studied the changes in foraging behavior associated with reproduction in female hoary bats, Lasiurus cinereus. As lactation progressed, individuals departed to forage earlier in the evening and spent more time foraging per night and less time roosting with their young. Foraging time increased by at least 73% between early lactation and fledging and then declined as the young became independent. Females with two young foraged for longer than did those with one and females with pre- and postfledging young foraged in different habitats. The changes in foraging time suggest that foraging activity of female L. cinereus is constrained and individuals act as time minimizers, adjusting their foraging behavior to meet current energy demand. Predation risk is unlikely to constrain the behavior of these bats. However, maximizing energy intake throughout lactation may not be the optimal strategy because storing excess energy increases flight cost and may reduce foraging efficiency. The need to keep newborn young warm may also influence foraging time. Such constraints, causing changes in foraging activity, may alter the availability of habitats and prey and must be considered when modelling foraging strategies. In addition, changes in flight time may significantly alter the energy budgets of bats in different stages of reproduction.

Roosting Behavior and Roost-Site Preferences of Forest-Dwelling California Bats (Myotis californicus)

We followed nine radiotagged female California bats ( Myotis californicus ) to 19 roosts in trees at two study sites in southcentral British Columbia. Bats regularly switched roosts and the number of bats emerging from known roosts fluctuated widely. Logistic-regression analysis showed that reproductively active females preferred trees further away from other trees of the same height or greater, and closer to neighboring trees, relative to available trees in the immediate vicinity of the roost. Diameter at breast height and distance to the nearest tree of the same or greater height explained significant proportions of the variation between roost and available trees found in other areas of the same forest stand. Roost trees had significantly larger diameters and were further away from trees of the same or greater height. Percentage of canopy closure also explained a significant proportion of the variation between roost and available trees, such that roost trees were situated in areas with lower canopy closure than available trees in other areas of the same stand. Roost and available trees were classified correctly >70% of the time based on the above tree characteristics. However, roost trees were only correctly classified 39% of the time in the analysis of site characteristics. Our results, combined with those from other recent studies, lead to the general hypothesis that forest-roosting bats require a number of large dead trees of specific species, in specific stages of decay, and that project above the canopy in relatively open areas. For management and conservation reasons, there should be a strong incentive to evaluate this hypothesis for a variety of species in a variety of locations to test its generality.

Substrate-gleaning versus aerial-hawking: plasticity in the foraging and echolocation behaviour of the long-eared bat, Myotis evotis

The foraging and echolocation behaviour of Myotis evotis was investigated during substrate-gleaning and aerial-hawking attacks. Bats gleaned moths from both the ground and a bark-covered trellis, however, they were equally adept at capturing flying moths. The calls emitted by M. evotis during substrate-gleaning sequences were short, broadband, and frequency-modulated (FM). Three behavioural phases were identified: search, hover, and attack. Gleaning search calls were significantly longer in duration, lower in highest frequency, and larger in bandwidth than hover/attack calls. Calls were detected in only 68% of gleaning sequences, and when they were emitted, bats ceased calling ∼ 200 ms before attacking. Terminal feeding buzzes, the rapid increase in pulse repetition rate associated with an attempted prey capture, were never recorded during gleaning attacks. The echolocation calls uttered by M. evotis during aerial-hawking foraging sequences were also short duration, high frequency, FM calls. Two distinct acoustic phases were identified: approach and terminal. Approach calls were significantly different from terminal calls in all variables measured. Calls were detected in 100% of aerial-hawking attacks and terminal feeding buzzes were invariably produced. Gleaning hover/attack calls were spectrally similar to aerial approach calls, but were shorter in duration and emitted at a significantly lower (but constant) repetition rate than aerial signals. Although the foraging environment (flight cage contents) remained unchanged between tasks (substrate-gleaning vs. aerial-hawking), bats emitted significantly lower amplitude calls while gleaning. We conclude that M. evotis adjusts its echolocation behaviour to meet the perceptual demands (acoustical constraints) imposed by each foraging situations.