The anti-predator behaviour of wild white-handed gibbons (Hylobates lar)

Abstract

Predation on gibbons is rarely observed in the wild. However, the gibbons' moderate body size and relatively small social groups suggest high vulnerability to predation. To assess the role of predation and to study their anti-predator behaviour, we presented visual predator models to nine groups of wild white-handed gibbons at Khao Yai National Park, Thailand. We measured subjects' immediate and delayed responses to four potential predators: tiger, clouded leopard, crested serpent eagle and reticulated python. Subjects reliably approached all four predators. In response to tigers and leopards, they additionally produced predator-specific songs and defecated copiously. In terms of delayed responses, distance between mated adults decreased, but only after exposure to the tiger model. In response to eagles and pythons, gibbons consistently vocalised, but this did not always include predator singing, and we found no long-term effects in overall activity or strata use. However, during 6 of 26 predator encounters, the gibbons produced songs with a structure that was intermediate between a duet song and a predator song more than 20 min after the predator encounter, indicating a long-term effect on their vocal behaviour. This study demonstrates that gibbons discriminate between different potential predators and respond to them with adaptive anti-predator behaviour, which include predator-specific vocal responses. We conclude that gibbons are not immune to predation and that terrestrial predators elicit consistent immediate and delayed anti-predation responses.

Raptors and primate evolution

“…Southeast Asian hawk‐eagles are considerably smaller than crowned eagles in Africa and harpy eagles of the Neotropics, which could explain why gibbons and adult colobines (for example, Rhinopithecus , Presbytis ) in Asia are at reduced predation risk . Indeed, field experiments showed that gibbons respond very strongly to clouded leopard and tiger models, but only weakly to crested serpent eagle models, suggesting that raptors may not be perceived as threats . Several large eagles have distributions that include those of gibbons; however, to date, no act of predation, by raptor or otherwise, has been witnessed at any gibbon study site …”

“…69 Indeed, field experiments showed that gibbons respond very strongly to clouded leopard and tiger models, but only weakly to crested serpent eagle models, suggesting that raptors may not be perceived as threats. 78 Several large eagles have distributions that include those of gibbons; however, to date, no act of predation, by raptor or otherwise, has been witnessed at any gibbon study site. 79 From taphonomic studies of extant prey and fossil assemblages, we have developed a good understanding of how owls and other raptors feed on and modify bones of small-bodiedand micro-mammals.…”

Contact calling behaviour in the male ring‐tailed lemur (Lemur catta)

“…Although one‐zero sampling has received criticism (e.g., Altmann, ), this sampling method has also been empirically shown to be an effective technique for collecting data on primate behavioural rates (Leger, ; Rhine & Linville, ; Sarfaty, Margulis, & Atsalis, ; Suen & Ary, ), and has been used in other studies on primate vocalisations (e.g., Bolt, ,c, ; Bolt et al., ; Clarke, Reichard, & Zuberbühler, ; Suzuki & Sugiura, ). We used one‐zero sampling because Bernstein () recommended that one‐zero scoring should be used when behavioural acts are clustered and the bout, rather than each act, is of interest.…”

Experimental field studies with non-human primates

“…For example, Clarke et al [78] found that Lar gibbons showed long-term behavioural effects hours after exposure to a predator model. A sensible way to avoid negative consequences is to work with stimuli that already occur regularly in the animals' natural lives.…”