Bat road casualties and factors determining their number

This paper examines 167 records of 14 bat species killed on roads in Poland. Regional differences in the species composition of road traffic accident records resulted from differences in the structure of local bat faunas. Young-of-the-year individuals (ind.) were killed significantly more often than adults. The highest mortality occurred in August and in the first half of September during intense dispersal of young bats. The highest incidence of road casualties was noted in places where roads crossed bat flyways, especially at junctions with forest edges and tree alleys. The rate of mortality depended on the habitat. It was highest where roads approached tree stands (up to 6.8 ind./km/year) or crossed a forest (2.7 ind./km/year) and lowest within densely built-up areas of Warsaw (0.3 ind./km/year). The mean was 1.5 ind./km/year in an 8-km section of a road near Warsaw. Road mortality depended on the hunting strategy of bats, in particular on the height of their flight. Road casualties were frequent for the low-flying gleaner, Myotis daubentonii (39.5% of the records), but rare for the high-flying aerial hawker, Nyctalus noctula (1.9%).