Tactile pup loss and acoustic signal enhance selective maternal retrieval behavior in echolocating bats, <i>Pipistrellus abramus</i>

Pup retrieval is a critical maternal behavior ensuring pup survival. Its mechanisms have been studied mainly in rodents, where mothers tolerate brief pup separation. In contrast, in species for which even short separation is life-threatening, mothers maintain constant physical contact, reinforcing anti-separation behavior. Studying such species may uncover maternal strategies under survival-critical extremes. Among these species, echolocating bats provide an ideal model for acoustic-based decision-making, as they rely heavily on sound. In bats, pup isolation calls (ICs) are essential signals in mother-pup communication. To assess their motivation in retrieval based on ICs, we conducted two behavioral experiments: (1) a pup retrieval test, and (2) a playback test using ICs from own versus non-own pups. Each was conducted under three maternal conditions to assess tactile influence on maternal motivation: holding (a) no pups, (b) one pup and (c) two pups. In pup retrieval tests, mothers showed selective responsiveness to their own pups, and it decreased with their pup development. Playback tests showed that acoustic signals alone were sufficient to elicit maternal responses, and their latencies were negatively correlated to pup vocalization rates. These maternal responses were strongly suppressed under condition c, but robustly expressed under conditions a and b. These findings suggest that maternal motivation is context-dependent responsiveness, which is enhanced by tactile pup loss and ICs, providing insight into instinctive maternal behavior in mammals.