Howling by the river: howler monkey (Alouatta palliata) communication in an anthropogenically-altered riparian forest in Costa Rica

The ways that forest edges may affect animal vocalization behaviour are poorly understood. We investigated the effects of various types of edge habitat on the loud calls (howls) of a folivorous-frugivorous primate species, Alouatta palliata, with reference to the ecological resource defence hypothesis, which predicts that males howl to defend vegetation resources. We tested this hypothesis across four forest zones - interior, riparian, anthropogenic, and combined forest edges - in a riparian forest fragment in Costa Rica. We predicted vegetation and howling would differ between forest zones, with riparian and interior zones showing the highest values and anthropogenic edge the lowest. Our results indicated that vegetation was richer and howling longer in riparian and interior zones compared to combined and anthropogenic edges, supporting the resource defence hypothesis and providing some of the first evidence in animal communication scholarship for differences in behavioural edge effects between natural riparian and anthropogenic edges.