Abstract
Although the negative impacts of roads on many terrestrial vertebrate and bird populations are well documented, there have been few studies of the road ecology of bats. To examine the effects of large roads on bat populations, we used acoustic recorders to survey bat activity along ten 300 m transects bordering three large highways in northern California, applying a newly developed statistical classifier to identify recorded calls to the species level. Nightly counts of bat passes were analyzed with generalized linear mixed models to determine the relationship between bat activity and distance from a road. Total bat activity recorded at points adjacent to roads was found to be approximately one-half the level observed at 300 m. Statistically significant road effects were also found for the Brazilian free-tailed bat (Tadarida brasiliensis), big brown bat (Eptesicus fuscus), hoary bat (Lasiurus cinereus), and silver-haired bat (Lasionycteris noctivagans). The road effect was found to be temperature dependent, with hot days both increasing total activity at night and reducing the difference between activity levels near and far from roads. These results suggest that the environmental impacts of road construction may include degradation of bat habitat and that mitigation activities for this habitat loss may be necessary to protect bat populations.
Highlights
Roads represent one of the most extensive human impacts on the biosphere and are one of the leading causes of habitat fragmentation [1,2]
More than 85% were identified by the random forest classifier as either Tadarida brasiliensis, the Brazilian free-tailed bat (40%), Eptesicus fuscus, the big brown bat (25%), Lasionycteris noctivagans, the silver-haired bat (15%), or Lasiurus cinereus, the hoary bat (7%) (Table 1)
A road effect of similar magnitude is predicted for T. brasiliensis, E. fuscus, and L. cinereus, while a larger effect is predicted for L. noctivagans
Summary
Roads represent one of the most extensive human impacts on the biosphere and are one of the leading causes of habitat fragmentation [1,2]. Research in the field of road ecology has quantified impacts such as direct mortality due to vehicle collisions, the prevention of physical movement and gene flow across landscapes, and decreases in the use of otherwise suitable habitat [3,4]. Two recent comprehensive reviews of the road effects literature have found that most studied species showed decreased abundance or activity levels in the vicinity of large roads, with effects extending to several hundred meters from the roadside and beyond [5,6]. The presence of vehicles on a road has been found to serve as a barrier during commuting and foraging [9,10,11], with species-specific responses to passageways across roads having been observed [12]. Lower levels of total bat activity and activity of the common Pipistrelle (Pipistrellus pipistrellus) have been observed within 1.6 km of a large road in Cumbria, United Kingdom [15]
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