Social implications of a colony collapse in a highly structured vertebrate species (long-tailed bat, Chalinolobus tuberculatus)

Strong social structuring within a population can confer fitness advantages to group members, but may also affect the ability of a population to recover from local extinctions. Opportunities to evaluate the dynamics of the collapse of a sub-population on a vertebrate population in the wild are rare, requiring a crash during a long-term study of marked individuals. Endangered long-tailed bats Chalinolobus tuberculatus, which are members of the widespread family Vespertilionidae, live in closed social groups as evidenced by non-random associations of individuals and a low degree of mixing among colonies. During a 19-year mark-recapture study of long-tailed bats in the Eglinton Valley, New Zealand, one colony of bats collapsed over a 2-year period in which numbers of introduced predators were high. We investigated individual- and colony-level implications of this local extinction event. Survivors (11 known) were assimilated into the neighbouring colony during and immediately after the collapse, but retained higher association rates with individuals from their former colony. The neighbouring colony gradually extended its roosting range into habitat formerly occupied by the extinct colony. Acceptance of individuals into other colonies demonstrates resilience of highly structured vertebrate populations to local crashes.