Brown Mouse Lemurs (Microcebus rufus) May Lack Opportunities to Learn about Predator Calls.

Diurnal primates commonly modify their behaviour in response to predator vocalizations, but little is known about how nocturnal primates perceive predator calls. Mouse lemurs do not innately perceive predator calls as dangerous but may learn to do so in the wild. I hypothesized that wild brown mouse lemurs (Microcebus rufus) in Ranomafana National Park, Madagascar, differentiate between predator and non-predator vocalizations and exposed 29 adult subjects to calls of 3 sympatric predators (goshawk, fossa and owl), 3 sympatric non-predators and 4 controls. Brown mouse lemurs did not differentiate among stimuli, and there was no evidence that any recording was associated with danger, as neither activity nor spatial preferences changed in response to a stimulus, nor did subjects exhibit obvious behaviours indicative of danger such as flight or position on the branches. The failure to perceive predator calls as dangerous is common among small nocturnal solitary prey species and could be explained by a lack of learning opportunities. In social species acquired behaviours can spread quickly by social learning. Solitary species like mouse lemurs have to individually learn to associate predator calls with danger which is dependent on encounter rates. Unlike diurnal prey mouse lemurs lack the opportunity to observe diurnal raptors and associate their calls with the bird, and owls are proficient predators, which are difficult to observe in a rain forest where they hunt cryptically from perches. While sometimes nocturnal, the fossa is solitary and largely silent, and is also particularly rare at my study site. Cryptic, rare or non-vocal predators provide prey with few opportunities to associate their calls with danger. Mouse lemurs are subject to high predation rates by a wide range of predators and need to balance the costs and benefits of antipredation behaviours. Their cryptic lifestyle and preference for dense vegetation lowers the likelihood of being detected by predators, and they utilize visual and olfactory predator cues to make decisions about risk. Furthermore, their high reproductive output compensates for the high predation rates.