Methods
We captured bats over a 12-week period between January 30th and April 14th, 2022, timed to encompass the short dry season (January to February) and the beginning of the long-wet season (March to May) in Taita-Taveta County, south-eastern Kenya (Tuure et al. 2020). We targeted M. condylurus and M. pumilus bats by netting at building and bridge roosts thought or known to contain these species (Figure 1). Bats were captured using mist nets (Ecotone 716/3-12P) set at or above roosting height (for buildings and bridges), and hand-held butterfly nets (Hyönteistarvike Tibiale Oy, 65cm net and 550cm telescopic pole) to block additional, smaller entrance/exit points of buildings not covered by mist nets (buildings only). Nets were either opened at dusk to capture bats leaving the roost to forage or opened from approximately one hour after dusk and operated through the night (17:30-22:30), to capture bats returning to the roost after foraging. Bats were removed from the nets immediately to minimize stress or injury. Where feasible, bats were also captured directly from roosting spaces during daytime hours by entering the roost space and removing as many as possible. Bats were held in individual cloth bags and sampled the morning following capture (for night netting), or the same day (in the case of daytime roost capture).
Demographic information (sex, age, and reproductive status) and standard measurements (weight and forearm length) were recorded for all captured bats. Age (juvenile or adult) was determined by evidence of current or previous reproduction, size, and ossification of the epiphyses (juveniles having an incomplete ossification, and adults having a complete ossification) (Anthony 1988; Monadjem et al. 2007). We categorised reproductive status into five states for females: non-reproductive, pregnant and not lactating, pregnant and lactating, lactating and not pregnant, and post-lactating. Nipples that were lactating were discernible by a bare patch of skin around an engorged nipple. Post-lactating nipples were those that appeared visibly engorged but did not have a bare patch of skin (i.e., not presently lactating but which might have lactated recently). Gestation was noted by gentle palpation of the abdomen. If a uterine bulge was present (not palpable on juveniles, subadults or males), pregnancy was classified as early (the uterine bulge was palpable but not significant), mid (the foetus was able to be felt, but the females’ abdomen did not extend past the ribs), or late (the foetus/bulge was obviously wider than the female’s rib cage). Females classified as non-reproductive were not detectably pregnant, lactating or recently lactating (i.e., without enlarged nipples). Species were identified following Patterson and Webala (2012).
Individuals of appropriate size (with a forearm length between roughly 31-54 mm) were banded (Porzana, Ltd., Icklesham, East Sussex, UK) with numbered, 2.9 mm, aluminium alloy, split-lipped rings to allow identification upon recapture. Post-processing, bats were released at the roost after dusk to reduce risk of predation. Personal protective equipment was worn at all times during capture, sampling, and release of bats. Procedures involving bat captures and handling followed established guidelines (Sikes et al. 2016). To characterise the birth pulse phenology in M. condylurus and M. pumilus bats, and evaluate the consistency of reproductive stage per week, we used chi-squared tests. Comparisons were made per week and included: 1) numbers of gestating and non-gestating females; 2) numbers of females at early, mid, and late gestational stages; 3) numbers of lactating and non-lactating females.