%0 Journal Article %T Circadian long call distribution in wild orangutans Distribution circadienne des cris longs (long calls) chez l¡¯orang-outan en milieu naturel %A Thomas Geissmann %A Marina Davila£¿Ross %J Revue de Primatologie %D 2009 %I Soci¨¦t¨¦ Francophone de Primatologie %R 10.4000/primatologie.219 %X We present first data on circadian long call distribution of wild orangutans in Northwest Borneo. Data were collected during two months in Batang Ai National Park. A total of 151 male long calls were heard, exhibiting a bimodal distribution pattern with peaks at 05:00-06:00 hours and 18:00-19:00 hours. An earlier study found pronounced differences between the calling rates of Bornean orangutans, which showed an almost unimodal call distribution with its peak at mid-morning, and those of Sumatran orangutans, which showed a bimodal call distribution with a distinct calling peak at predawn and a more moderate peak near dusk (MacKinnon 1974). Our findings from Batang Ai resemble more closely the pattern reported for Sumatra than those reported for other Bornean localities and, therefore, contradict earlier reports suggesting a Sumatra-Borneo dichotomy in orangutan call distribution. In addition, orangutans in Batang Ai were heard to regularly emit long calls throughout the night. This behaviour is unusual for a diurnal species. Nous pr¨¦sentons les premi¨¨res donn¨¦es sur la distribution circadienne des cris longs (long calls) chez les males orangs-outans vivant en milieu naturel au nord-ouest de Born¨¦o. Les donn¨¦es ont ¨¦t¨¦ r¨¦colt¨¦es lors d¡¯une ¨¦tude de terrain de deux mois au Parc National de Batang Ai. Les 151 cris longs entendus montraient une distribution bimodale, caract¨¦ris¨¦e par des pics ¨¤ 05:00-06:00 et 18:00-19:00 heures. Une ¨¦tude pr¨¦c¨¦dente avait r¨¦v¨¦l¨¦ des diff¨¦rences profondes entre les taux de cris longs des orangs-outans de Born¨¦o et de Sumatra. Alors que la distribution des cris longs ¨¤ Born¨¦o ¨¦tait presque unimodale et montrait un pic en milieu d¡¯avant-midi, la distribution ¨¤ Sumatra ¨¦tait bimodale et montrait un pic distinct avant l¡¯aube et un second pic plus mod¨¦r¨¦ au cr¨¦puscule (MacKinnon 1974). Nos r¨¦sultats ¨¤ Batang Ai ressemblent davantage au sch¨¦ma rapport¨¦ pr¨¦c¨¦demment ¨¤ Sumatra qu¡¯¨¤ ceux rapport¨¦s pour les autres localit¨¦s de la r¨¦gion de Born¨¦o. En cons¨¦quence, ils contredisent les r¨¦sultats pr¨¦c¨¦dents qui sugg¨¨rent une dichotomie Sumatra-Born¨¦o dans la distribution des cris longs chez l¡¯orang-outan. De plus, nous avons not¨¦ que les orangs-outans de Batang Ai ¨¦mettent des cris longs pendant la nuit, comportement inhabituel pour une esp¨¨ce diurne. %K orangs-outans %K cris longs %K distribution temporelle des cris %K rythmes circadiens %K comp¨¦tition intersp¨¦cifique %K diff¨¦rences entre populations %K orangutans %K Pongo spp. %K long call %K calling time %K circadian rhythms %K interspecific competition %K population differences %U http://primatologie.revues.org/219