R. Mark Brigham

Roost switching, roost sharing and social cohesion: forest-dwelling big brown bats, Eptesicus fuscus, conform to the fission–fusion model

We used radiotelemetry to quantify roost switching and assess associations between members of maternity colonies of forest-dwelling big brown bats. Bats remained loyal to small roosting areas of forest within and between years and switched trees often (XG SD ¼ 1:7G 0:7 days). For radiotagged bats from the colony in one of these areas, roost-switching frequency was positively correlated with the number of different individuals with which tagged bats shared roosts. We quantified associations between pairs of bats using a pairwise sharing index and found that bats associated more often than predicted when roost and roostmate selection were random but that all tagged bats spent at least some days roosting in different trees, apart from preferred roostmates. Our results suggest that forest-dwelling big brown bats conform to a fissionefusion roosting pattern. Roost switching in forests may reflect the maintenance of long-term social relationships between individuals from a colony that is spread among a number of different trees on a given night. In this fissionefusion scenario, switching between trees, within a local area, could serve to increase the numbers of individuals with which bats maintain associations. We contend that roosting areas in forests are analogous to spatially large roosts in caves, mines and buildings.

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

PATHOLOGY, ISOLATION, AND PRELIMINARY MOLECULAR CHARACTERIZATION OF A NOVEL IRIDOVIRUS FROM TIGER SALAMANDERS IN SASKATCHEWAN

An iridovirus was confirmed to be the cause of an epizootic in larval and adult tiger salamanders (Ambystoma tigrinum diaboli) from four separate ponds in southern Saskatchewan (Canada) during the summer of 1997. This organism also is suspected, based on electron microscopic findings, to be the cause of mortality of larval tiger salamanders in a pond over 200 km to the north during the same year. Salamanders developed a generalized viremia which resulted in various lesions including: necrotizing, vesicular and ulcerative dermatitis; gastrointestinal ulceration; and necrosis of hepatic, splenic, renal, lymphoid, and hematopoietic tissues. In cells associated with these lesions, large lightly basophilic cytoplasmic inclusions and vacuolated nuclei with marginated chromatin were consistently found. Virus was isolated from tissue homogenates of infected salamanders following inoculation of epithelioma papilloma cyprini (EPC) cells. The virus, provisionally designated Regina ranavirus (RRV), was initially identified as an iridovirus by electron microscopy. Subsequent molecular characterization, including partial sequence analysis of the major capsid protein (MCP) gene, confirmed this assignment and established that RRV was a ranavirus distinct from frog virus 3 (FV3) and other members of the genus Ranavirus. Intraperitoneal inoculation of 5 × 106.23 TCID50 of the field isolate caused mortality in inoculated salamanders at 13 days post infection. Field, clinical, and molecular studies jointly suggest that the etiological agent of recent salamander mortalities is a highly infectious novel ranavirus.

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.

Tree roost selection by bats: an empirical synthesis using meta-analysis

Abstract Over the past 2 decades, we have begun to accumulate a basic understanding of the roosting and foraging ecology of temperate insectivorous bats in forests. As our understanding improves, it is not surprising there should be attempts at synthesizing our knowledge to prioritize future research directions (e.g., Hayes 2003-,-->Miller et al. 2003). -->Miller et al. (2003) reviewed results of 56 papers (1980–2001) and concluded that current data were unreliable because of small sample sizes, the short-term nature of studies, pseudoreplication, inferences beyond the scale of data collected, study design, and limitations of bat detectors and statistical analyses. Our concern is that this type of narrative synthesis that highlights limitations ignores any quantitative patterns that may exist. In this study we assess whether general patterns in North American bat use of roost trees and stand characteristics are robust enough to distill from the published literature. We used a series of meta-analyses on the same set of studies cited by Miller et al. (2003) to assess whether limitations of the current data warrant exclusion of bats from management recommendations. We used a second series of meta-analyses incorporating more recent data to determine the best current synthesis of knowledge on bat use of forests for roosting. In a third and fourth series of meta-analyses, we separated studies done on bats roosting in cavities versus roosting in foliage. In general, we found that, relative to other trees in the forest, the roost trees of bats were tall with large DBH in stands with open canopy and high snag density. In contrast, roost trees of bats did not differ from random trees with respect to live-tree density. The main differences we detected between foliage and cavity-roosting bats were in percent canopy cover and distance to water. The roost trees of cavity-roosting species had more open canopies and were closer to water than random trees. Our results clearly show that significant patterns can be detected from the literature when data sets are combined using a meta-analytic approach.

Deep, prolonged torpor by pregnant, free-ranging bats.

Many mammals save energy during food shortage or harsh weather using controlled reductions in body temperature and metabolism called torpor. However, torpor slows offspring growth, and reproductive individuals are thought to avoid using it because of reduced fitness resulting from delayed offspring development. We tested this hypothesis by investigating torpor during reproduction in hoary bats (Lasiurus cinereus, Vespertilionidae) in southern Canada. We recorded deep, prolonged torpor bouts, which meet the definition for hibernation, by pregnant females. Prolonged torpor occurred during spring storms. When conditions improved females aroused and gave birth within several days. Our observations imply a fitness advantage of torpor in addition to energy conservation because reduced foetal growth rate could delay parturition until conditions are more favourable for lactation and neonatal survival.

Can External Radiotransmitters Be Used to Assess Body Temperature and Torpor in Bats

We tested externally applied, temperature-sensitive, radiotransmitters for determining the body temperature of big brown bats ( Eptesicus fuscus ) in various ambient temperatures (2–26°C). There was a slight, but significant, effect of ambient temperature on skin temperature (measured by the transmitters), but skin temperature accurately reflected rectal temperature in torpid and active bats, and it was never >3.3°C below rectal temperature. External radiotransmitters are, thus, useful in studies of torpor in bats, even when only small decreases in body temperature occur.

Physiological and ecological aspects of roost selection by reproductive female hoary bats (Lasiurus cinereus)

Abstract Most recent research on the roosting habits of temperate, forest-living bats has focused on species that use enclosed cavities, but less has been done to address roosting by foliage-living species, which are assumed to have more flexible roost requirements. Numerous studies have suggested that bats select roosts on the basis of microclimate, yet few have tested this hypothesis empirically and none have addressed the use of foliage roosts in this context. We used radiotelemetry to locate roost sites of reproductive female hoary bats (Lasiurus cinereus) then compared a variety of physical features of these trees with randomly selected nonroost trees. We also recorded ambient temperature and wind speed at roost and nonroost sites to test the hypothesis that physical features associated with foliage roosts provide energetic benefits. Hoary bats selected roost sites on the southeast side of mature white spruce trees (Picea glauca; X̄ orientation 158.6 ± 6.3° SSE). Roost trees were more likely than random trees to be the same height as the surrounding forest canopy; had less canopy cover facing out from the tree in the direction of the roost branch; and had lower forest density on their southeast side. Wind speed was significantly lower at roosts sites compared with opposite sides of the same trees, presumably due to increased protection from prevailing west winds. Incorporating an estimate of convective cooling due to wind, we predicted daily thermal energy expenditure for normothermic bats and found that selected roost sites provided statistically significant energy savings (up to 1.60 ± 0.99 kJ/day) relative to the predicted expenditures if bats had roosted on the opposite sides of trees. Our results provide direct evidence that hoary bats select forest roosts on the basis of microclimate and suggest that roost requirements of foliage-roosting species may be more specific than has been previously assumed.

Do Patterns of Torpor Differ between Free-ranging and Captive Mammals and Birds?

Most studies on torpor in mammals and birds have been conducted in the laboratory. We compared whether patterns of torpor of several mammals and birds differ between the laboratory and field. Our comparison shows that in most species patterns of torpor in the laboratory differ substantially from those in the field. Some species, even if they use torpor extensively in the field, appear most reluctant to enter torpor in captivity. Moreover, torpor in the field is often more frequent, deeper, and longer than in captivity. Our comparison suggests that laboratory studies are likely to underestimate use and depth of torpor in the wild and thus may underestimate its impact on energy expenditure and survival.

Short-Term Effects of Small-Scale Habitat Disturbance on Activity by Insectivorous Bats

Forest harvesting alters habitat, which may affect bat activity. We experimentally tested the effect of small-scale disturbances (the creation of small cutblocks [areas where trees have been harvested]) and an access road in a forest setting on habitat use by bats we monitored with ultrasonic detectors. Relative to the control year, bat activity increased (P < 0.05) in the summer after cutblocks and the road were created, but activity did not vary with cutblock size (0.5, 1.0, and 1.5 ha). In contrast to bat activity, insect availability was unaffected by harvesting activities. These results suggest small forest openings may offer opportunities for bats to forage and provide orientation points for bats while navigating at a landscape level. However, the long-term effects of larger-scale habitat disturbances on bat ecology are still unclear, and caution should be exercised when applying these results to forest management plans.