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

Abstract

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 ®rst¯ight lasted the longest. During preparturition, when distances from roost to foraging site were greatest, and time spent¯ying per night (t F ) was least, there was often only one¯ight, with a second towards dawn on warmer nights, and occasionally a third. After parturition, in June, t F and the number of¯ights (N F ) 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. N F fell to preparturition levels after lactation. Exploratory behaviour by juveniles intensi®ed with time ± distances to feeding sites, t F and the total distance¯own each night all increased; the distance¯own 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.

Reproductive and age classes do not change spatial dynamics of foraging long-fingered bats (Myotis capaccinii)

“…It has previously been shown that the foraging range of female bats changes during lactation, although it may either decrease (Racey and Swift 1985;Shiel et al 1999;O'Donnell 2001;Henry et al 2002) or increase (Clark et al 1993;Jones et al 1995;Goiti et al 2006) compared with previous seasons. Both the increased energy demands due to milk production and the need to return repeatedly to the roost to feed their pups during the night are thought to affect the spatial behaviour of foraging females (Racey and Swift 1985;Shiel et al 1999;O'Donnell 2001;Henry et al 2002;Goiti et al 2006). Surprisingly, in our research, the increased energy costs of lactation did not promote a distinct spatial behaviour in lactating females compared with other bats during the same period.…”

“…Most studies on bats' spatial foraging hitherto conducted have not split the effects of period and class on that behaviour (e.g., Racey and Swift 1985;Audet 1990;Shiel et al 1999;Henry et al 2002), and comparison of classes from different biological periods may have led to misleading conclusions about the singular foraging strategy of some classes, e.g., lactating females or juveniles. The design of the present study splits the two potential sources of variation (individual class and period) and thus allows a more accurate interpretation of behavioural differences between classes.…”

“…During the spermatogenic phase, male Myotis daubentonii use larger foraging ranges compared with other classes Dietz and Kalko 2007). Contrasting results on relative size of foraging range in lactating females have been observed across studies, and specific lactation behaviour and surveyed colony size were suggested to be responsible for that variability (Shiel et al 1999;O'Donnell 2001;Fellers and Pierson 2002;Henry et al 2002;). Furthermore, spatial use shown by young individuals (2-4 months old) has been attributed to exploratory behaviour, presumed to be typical at this stage (Audet 1990;Jones et al 1995;Shiel et al 1999;O'Donnell 2001;Goiti et al 2006).…”

“…Some stages in the bat's life cycle (typically lactation or spermatogenesis) require a higher energetic intake (Kurta et al 1989;Kurta et al 1990;Speakman and Thomas 2003;Encarnação and Dietz 2006). Accordingly, lactating females and spermatogenic males have usually been found to spend more time foraging compared with other individuals (Rydell 1993;Shiel et al 1999;Barclay et al 2000;Encarnação and Dietz 2006; but see Dietz and Kalko 2007). During the spermatogenic phase, male Myotis daubentonii use larger foraging ranges compared with other classes Dietz and Kalko 2007).…”

“…The effect of time-that is, periods or seasons of different biological meaning-and animal classes on spatial behaviour have not been separately studied in most investigations dealing with the spatial ecology of foraging bats (e.g., Racey and Swift 1985;Audet 1990;Shiel et al 1999;Henry et al 2002). This means, for instance, that differences in home range or foraging time between pregnant and lactating females will not necessarily correspond to differences in energetic requirements, unless environmental features are similar during the two periods.…”