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

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 behavioral experiments: (1) pup retrieval test, and (2) playback test using ICs from own vs. non-own pups. Each was conducted under three maternal conditions: holding (a) no-pup, (b) one-pup, and (c) two-pup, to assess tactile influence on maternal motivation. Mothers responded only during periods of high-rate ICs vocalization and showed selective responsiveness to their own pups. ICs alone were sufficient to elicit maternal responses, acted as decisive communicative triggers for maternal response. Maternal responses were strongly suppressed under condition (c), but robustly expressed under conditions (a) and (b). These findings suggest that maternal motivation is governed by a decision-making threshold, whereby internal motivation induced by pup loss is amplified by ICs, a decisive trigger for retrieval--providing insight into instinctive maternal behavior in mammals.