Evening emergence of two nursery colonies of Leisler's bat (Nyctalus leisleri) in Ireland

Abstract

At one nursery roost of Leisler's bat Nyctalus leisleri, the ®rst bat often, and over half of the colony exceptionally, left before sunset. Departure was earlier during the period of lactation, when energy demands were highest. Consequently emergence data had to be standardized to allow for this before investigating possible associations with light intensity and meteorological factors. The importance of such standardization in general is emphasized. Emergence was earlier on overcast nights and was delayed with increased light intensity. The bats in a neighbouring roost, from which fewer data were obtained, also left earlier on overcast evenings, but departure was generally later than in the ®rst roost, and there was no evidence of its being earlier during lactation. These differences between the roosts may be at least partially explained by the difference in size of the exit holes. At both roosts departure was mainly as a series of outbursts, and this was more marked during the ®rst half of emergence. Rate of emergence increased with colony size. It was unusual for the ®rst bat to leave more than 30 min, or for any bat to leave over 60 min, after sunset. Heavy rain inhibited or disrupted emergence.

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

“…In 1994 there was also an increase in N F over lactation (Spearman's rank correlation r' = 0.613, n = 14, P < 0.05). While this was not the case in 1995, parturition occurred unexpectedly early (Shiel & Fairley, 1999) and the ®rst nursing female was not tagged until more than a week after lactation had commenced. With postlactation N F fell; of the 14 nights with data, there were one to three¯ights on all but one night, when there were six¯ights, but it then rained intermittently and the bat used temporary night roosts four times.…”

“…Anyway, this may be as ef®cient as travelling indirectly, but at a speed nearer V mr , along linear landscape features. As N. leisleri often emerges before sunset (Shiel & Fairley, 1999), fast¯ight may be of particular importance in avoiding predation from diurnal birds. In addition, in the evening, rapid commuting¯ight would increase the time spent foraging during the insect peak at dusk.…”

“…Peak numbers in nursery colonies are reached when all young are volant and before adult females have started to desert the roost. The maximum number of bats counted during evening emergence at Baldwinstown was 152 in 1994 on 15 July, and 173 in 1995 on 9 July (Shiel & Fairley, 1999).…”

“…The bats left via a hole between wall and facia board, again on a gable. The maximum number of bats counted was 115 in 1994 on 15 July, and 175 in 1995 on 2 July (Shiel & Fairley, 1999).…”

Roosting behaviour and phenology of the Lesser horseshoe bat (Rhinolophus hipposideros) in a breeding colony in Sintra, Portugal

“…In fact, the availability of aerial insects, daylight-length (McAney & Fairley 1988, Catto et al 1995, temperature (Lacki 1984, Russo & Jones 2003, Russ et al 2003, and other climatic factors as rainfall (Shiel & Fairley 1999), relative humidity (Lacki 1984) and wind speed (Russ et al 2003, Russo & Jones 2003 seemed to play an important role in the activity patterns of insectivorous bats. Some studies show that insectivorous bats present this bimodal pattern due to the exploitation of peaks of activity of aerial insects: a first peak in the number of insects usually occurs after dusk and a second just before dawn (Swift 1980, Rautenbach et al 1988, Jones & Rydell 1994).…”