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Northern Long-eared Bat

Limiting Factors

Northern Long-eared BatIn general, bat distributions and abundance in Canada tend to be limited by climate and availability of suitable roost sites. Overlying this trend is a pattern of decreased diversity and abundance of bats with increasing latitude north of the equator. As such, in the northern temperate regions of Canada, the number of bat species and individuals is relatively low. The  average annual growing season is approximately 120 days; that is, the period during which the daily temperature remains above 6 degrees Celsius. This appears to reflect the minimum time needed for female bats to produce young and have them successfully grow and develop to the stage where they can survive hibernation. Thus climate may be the ultimate limiting factor on the northern distribution of Northern Long-eared Bats.

Similarly, the size of the population of Northern Long-eared Bats in Alberta will also be limited by geography and latitude. Estimates of population are further hampered by the fact that the species is a forest-dwelling bat that is difficult to find. 

The availability of suitable hibernacula may be a limiting factor in Northern Long-eared Bat Northern Long-eared Bat populations as well. Abandoned mines or natural caves may be in short supply over much of the species' range in northern Alberta. In addition, environmental conditions necessary for successful hibernation make many mines and caves unsuitable. When the number of hibernacula is low, bat populations are disproportionately clumped at a time when they are most vulnerable. This increases the risk that catastrophic impact may seriously reduce the population. 

Hibernating bats are particularly sensitive to disturbance. They have limited stored energy supplies and have no opportunity to replace energy expended during the winter. In order to conserve energy, Northern Long-eared Bats are true hibernators. That is, they enter a state of torpor where their internal body temperature approaches freezing, their breathing and heart rate are significantly slowed, and all unnecessary movement is avoided. Bats will, however, arouse from torpor to seek water, move to another location if environmental conditions become unsuitable (for example, if the hibernaculum becomes too warm or too cold), or if they are physically disturbed. Most often this latter disturbance is related to human activity within the hibernaculum.

The closing or otherwise altering of old mines or caves that are essential for hibernation may also limit the numbers of surviving Northern Long-eared Bats. Although there are no records of closures of known bat hibernacula in Alberta, such situations have occurred elsewhere. Furthermore, our lack of knowledge regarding the hibernation sites of the Northern Long-eared Bat in Alberta could lead to unintentional disturbance or destruction of hibernacula. Changes to the internal environment within a hibernaculum also may result in its abandonment by the bats.

Although the boreal forest covers a vast area, it is difficult to assess either the proportion of forest that can be considered suitable habitat for this species, or the impacts that may result from various resource extraction activities (such as forestry). `

Reprinted from Alberta Wildlife Status Report No. 3, with permission from Alberta Sustainable Resource Development.

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