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-trac ked from April to August in 2 years. They commuted directly to foraging sit es up to 13.4 km away at speeds often exceeding 40 km h(-1) Except during l actation, individuals occasionally day-roosted away from the nursery in bui ldings or hollow trees. These were also sometimes used as night roosts, esp ecially during rain, which also stimulated return to the nursery. On most n ights the first flight lasted the longest. During preparturition, when dist ances from roost to foraging site were greatest, and time spent flying per night (t(F)) was least, there was often only one flight, with a second towa rds dawn on warmer nights, and occasionally a third. After parturition, in June, t(F) and the number of flights (N-F) increased up to weaning, corresp onding to rising energy demands. But distances to foraging sites fell, risi ng only slightly in postlactation, presumably because insects, and thus fee ding patches, were more abundant than in preparturition. N-F fell to prepar turition levels after lactation. Exploratory behaviour by juveniles intensi fied with time - distances to feeding sites, t(F) and the total distance fl own each night all increased; the distance flown each night was eventually greater than any recorded for adults. Roosting away from the nursery was al so more common. Before dispersal, there were extended migrations by juvenil es outside the summer range of the adults. Distances moved by two dispersed juveniles exceeded 34 km. Two-thirds of the recorded foraging time was ove r pasture or drainage canals. Foraging over other habitats, particularly la ke and conifer forest, was greatest in preparturition. Other habitats forag ed included lights, estuary, stream, beach and dunes.