echoes bouncing back can interrupt the new echoes being sent out, causing confusion for the animal and preventing the system from working correctly. This issue does not occur when the bats are mid-air, as the sound has more distance to travel, and fewer objects could disrupt the signal or cause confusion. Life cycle and social systems Social systems and mating behaviour Lesser short-tailed bats form fission-fusion societies. This means populations will congregate at certain times, separate, and recongregate later. Where these animals group together are known as roosts. For roosting, they prefer to find trees with large internal cavities, where they create their ‘home’. A roosting site will contain multiple trees within the same general vicinity. The number of individuals present at a roosting site vary greatly, with some colonies consisting of hundreds or thousands of individual bats. Male bats attempt to attract a mate during the spring and summer months before mating begins, which is usually during autumn (March-May in New Zealand). Like many other species, the males attract mates at night by using vocal calls. The males will sing from one of the roosting trees within the colony for several minutes. Multiple males will aggregate at this same roost, taking turns singing. This behaviour is classified as a lek breeding system. In this type of mating, sexual selection occurs, as the males signal to potential females in the hopes they will be impressed and mate with the male. Lek breeding is how the male bats ‘prove their worth’. The mating events that follow are non-monogamous, and males have been observed to mate with multiple different females. While lek breeding systems are observed throughout the animal kingdom, they are rare in bats and have only been observed in one other species. Early life and life cycle Lesser short-tailed bat pups become active within a day of being born. For the first two days, they are hairless, with underdeveloped teeth, wings, and ears. The pups are capable of flying within roughly four weeks. Six weeks post-birth, they leave the maternity roosts they were raised in. After a few months they have reached their adult body size. The pups are born in summer (December-February in New Zealand). During this summer birthing period, the dispersed individuals will regroup, forming a large colony. Pups will feed first on milk produced by their mothers. Each mother will give birth to a single pup per