Effects of bat-bands and banding on a population of Pipistrellus nanus (Chiroptera : Vespertilionidae) in Malawi

This study provides information about the effects of flanged metal bat-bands, and the procedures associated with banding and frequent censusing, on a population of Pipistrellus nanus, a particularly small vespertilionid bat. The bats were censused at their roosts in a banana plantation, at intervals of approximately two weeks, for 10 months; 120 bats were banded and 75 were recaptured (447 recaptures). The best data came from a cohort of 64 adults (banded during the first six censuses), 25 of which were recaptured 9-15 times. Band-status (the effect of the band on the bat) was recorded each time a bat was captured. We recognised four classes of band-status ranging from class 1 (band-free with no injuries, observed on 66% of occasions) to class 4 (band-immobile with an unhealed wound, observed on 11% of occasions). Analyses of the results showed that (a) the majority of bats were in class 1 on most occasions, but some had injuries (classes 2-4) which often improved or deteriorated unpredictably; (b) the band-status changed in relation to time after banding, following an unexplained pattern; (c) band-status was not affected by seasonal changes in climate, or by the sex of the bat; (d) banding did not affect flight and foraging, or mass, or "survival" in the population; and (e) roosting behaviour was not adversely affected. Bats banded when we were inexperienced (census 1) were more prone to injuries than bats banded when we had improved our banding technique. Banding enabled us to study the social behaviour and reproduction of this species and we believe that the results justified banding one small population of this common, widespread species. We predict that other species of small vespertilionids may respond similarly to banding, but extrapolation to species in other families is probably not justified. We recommend that flanged bat-bands should be fitted as loosely as possible, that new bat-banders should be trained by experienced banders, and that banding of bats is permitted only when there are very good scientific reasons for the banding and when harm to individual bats and populations is likely to be minimal.