Evolution of contact and alarm calls in the Kenyan endemic Hinde's babbler (Aves: Passeriformes).

Our data show that call differentiation is governed by geographic isolation as well as altitude. Diverging degrees of call differentiation in contact and alarm calls suggests that both call types are under different selective pressures. Alarm calls are required to be understood by all members of the species across the entire distribution range and thus call differentiation is lower. In contrast, contact calls are more specific and differ even among neighbouring families supporting the maintenance of distinct bird families and groups.