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1

The influence of a local temperature inversion on the foraging behaviour of big brown bats, Eptesicus fuscus

100%
Arbuthnott D., Brigham R. M.
Acta Chiropterologica
|
2007
|
tom 09
|
nr 1
To maximise foraging efficiency, it is reasonable to expect animals to forage in the highest quality patches. Insectivorous bats should therefore travel to and forage at sites with the highest insect abundance. Since insects are ectothermic, their levels of activity should be higher in warmer areas, making these high quality patches for bats. A nightly temperature inversion occurring in the Cypress Hills (Saskatchewan, Canada) presented an opportunity to test our hypothesis that big brown bats (Eptesicus fuscus) select foraging sites based on temperature as a proxy for insect abundance. If temperature is an important determinant of the foraging behaviour of E. fuscus, we expect bats to forage in the warmest site closest to local night roosts. We tracked 18 bats for a total of 111 nights over two years and found that individuals often spent at least some of each foraging bout in an area where the temperature inversion was small or non-existent. Bats sometimes travelled up to 11 km to reach this site. Foraging in areas where the temperature inversion was small provides indirect evidence that local temperature fluctuations are not a major influence on the selection of foraging area by E. fuscus. Also, since there was little difference in the temperature between the nearby predicted foraging sites and actual foraging sites, we argue that the effect of temperature on insect activity cannot be used to predict foraging habitat selection by these bats. We found that the insect community of the foraging area was different than that of the roosting area, and that beetles were more abundant in the foraging site. Our data suggests that insect community composition is potentially a stronger direct influence on bat foraging behaviour than is temperature.
2

Cavity roost site availability and habitat use by bats in different aged riparian cottonwood stands

81%
Swystun M. B., Lane J. E., Brigham R. M.
Acta Chiropterologica
|
2007
|
tom 09
|
nr 1
Riparian forests provide important roosting habitat, abundant prey and access to drinking water for many bat species but to date there has been little research on the differential quality of habitats within riparian areas. We quantified the density of potential roost cavities in three age classes (i.e., young: ca. 20 years, mature: ca. 60 years, and old: ca. 100 years) of riparian cottonwood (Populus deltoides) forest stands. Bat activity was also sampled using acoustic detectors in one representative stand of each age class. Stands were situated along an 80 km stretch of the Missouri River in southeastern South Dakota and northwestern Iowa, USA. We predicted the highest density of potential roosts and the highest activity of bats to occur in the oldest age class. Contrary to our predictions, and previous work in aspen dominated upland sites, we found that the density of potential roosts was not significantly different between mature and old stands. However, there were no potential roosts in young stands. Data from guano traps verified the use of a number of cavities in both mature and old stands. Both commuting and foraging activities were highest in the mature, relative to the old and young stand. In total, our data indicate that mature and old stands represent high quality roosting habitat, with the mature being used preferentially for commuting and foraging. Trees in the oldest stands, however, are nearing the end of their lifespan and falling. Younger cohorts must therefore be retained for future recruitment of natural cavities.
3

The influence of residual tree patch isolation on habitat use by bats in central British Columbia

81%
Swystun M. B., Psyllakis J. M., Brigham R. M.
Acta Chiropterologica
|
2001
|
tom 03
|
nr 2
One forest management practice associated with logging aimed at contributing to the maintenance of biodiversity is to leave residual tree patches within cut blocks. Using Anabat bat-detectors we monitored bat activity along residual tree patch edges and clear-cut edges associated with recent clear-cuts in north-central British Columbia. We tested two hypotheses, (1) relative bat activity would be higher on the clear-cut edge than the residual patch edge, (2) relative bat activity would decrease on the residual patch edge with increasing isolation from the clear-cut edge. We sampled six pairs of edges and found no significant difference in bat activity between patch and clear-cut edges. We found a significant but non-linear relationship between relative bat activity on the patch edge with increasing patch isolation. Bat activity on the residual patch edge was highest at intermediate levels of patch isolation and lower both at patch edges close to, and highly isolated from the clear-cut edge. We postulate that the reason for this relationship is that patches act as windbreaks collecting high densities of insects making them good foraging areas but this benefit is coupled with an increased risk of prédation associated with crossing large gaps. At low levels of patch isolation bats may perceive residual patches and adjacent clear-cut edges as a continuous foraging area and thus, bat activity is evenly distributed throughout both habitats. In summary, our data indicate that patches provide localized habitat for foraging bats, however, foraging areas are only one habitat component required by bats and it remains uncertain if patches also offer suitable roosting opportunities.
4

Medium- and long-term reuse of trembling aspen cavities as roosts by big brown bats (Eptesicus fuscus)

71%
Willis C. K. R., Kolar K. A., Karst A. L., Kalcounis-Rueppell M. C., Brigham R. M.
Acta Chiropterologica
|
2003
|
tom 05
|
nr 1
Roost availability may limit some bat populations, implying that there may be a selective advantage associated with the ability to reuse sites on an annual basis. We monitored aspen tree use by Eptesicus fuscus during multi-year studies (spanning up to 10 years) at the same site in Saskatchewan, Canada. We found that reuse of live trees over the medium-term (three years) was common and that, in some instances, reuse over the long-term (nine and 10 years) can occur. Our data also suggest that, over the medium-term, aspen roosts are reused by groups of bats more often than by solitary individuals. Our findings support the hypothesis that cavity roosting bats exhibit between year loyalty, not just to patches of forest but also to specific trees.
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