Seasonal changes in the foraging behaviour of Leisler's bats (Nyctalus leisleri) in Ireland as revealed by radio-telemetry



Leisler's bats Nyctalus leisleri, from two nursery colonies were radio-tracked from April to August in 2 years. They commuted directly to foraging sites up to 13.4 km away at speeds often exceeding 40 km h-1. Except during lactation, individuals occasionally day-roosted away from the nursery in buildings or hollow trees. These were also sometimes used as night roosts, especially during rain, which also stimulated return to the nursery. On most nights the first flight lasted the longest. During preparturition, when distances from roost to foraging site were greatest, and time spent flying per night (tF) was least, there was often only one flight, with a second towards dawn on warmer nights, and occasionally a third. After parturition, in June, tF and the number of flights (NF) increased up to weaning, corresponding to rising energy demands. But distances to foraging sites fell, rising only slightly in postlactation, presumably because insects, and thus feeding patches, were more abundant than in preparturition. NF fell to preparturition levels after lactation. Exploratory behaviour by juveniles intensified with time – distances to feeding sites, tF and the total distance flown each night all increased; the distance flown each night was eventually greater than any recorded for adults. Roosting away from the nursery was also more common. Before dispersal, there were extended migrations by juveniles outside the summer range of the adults. Distances moved by two dispersed juveniles exceeded 34 km. Two-thirds of the recorded foraging time was over pasture or drainage canals. Foraging over other habitats, particularly lake and conifer forest, was greatest in preparturition. Other habitats foraged included lights, estuary, stream, beach and dunes.