Diurnal distribution of loud calls in sympatric wild indris (Indri indri) and ruffed lemurs (Varecia variegata): implications for call functions.

We carried out a short study on the diurnal call distribution of two sympatric lemurs in the Réserve Naturelle Intégrale Zahamena (eastern Madagascar). Whereas indris (Indri) song bouts were clearly concentrated in the early morning hours, the roar/shriek choruses of ruffed lemurs (Varecia) exhibited a much more even distribution throughout the day. These differences in distribution pattern support earlier claims that indri song bouts are more likely to serve territorial functions, whereas ruffed lemur loud calls may serve both spacing and/or alarm call functions.