Abstract
BackgroundSpatial isolation, diverging environmental conditions and social structures may lead to the differentiation of various traits, e.g. molecules, morphology and behaviour. Bird calls may provide important information on effects of geographic isolation and may reflect diverging ecological conditions related to altitude. Furthermore, bird calls are strongly shaped by the social behaviour of species. The Kenyan endemic bird Hinde’s Babbler, Turdoides hindei, is a cooperative breeder existing in distinct family groups. The species occurs in five isolated population groups at different altitudes across its distribution range in south-eastern Kenya. With this model species we test for potential effects of geographic isolation, diverging altitudes, and social structures. We recorded and analysed contact and alarm calls of T. hindei, including its entire distribution range and all existing population groups.ResultsOur data show significant differentiation of call characteristics among population groups across the species’ distribution range. This differentiation is correlated with geographical distance, but also with altitude. We also found strong call differentiation among neighbouring family groups. Call differentiation of contact calls was comparatively high in comparison to alarm calls, which showed a lower degree of divergence.ConclusionOur 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.
Highlights
Spatial isolation, diverging environmental conditions and social structures may lead to the differentiation of various traits, e.g. molecules, morphology and behaviour
We considered its entire distribution range across south-eastern Kenya [10] and recorded individuals belonging to 20 families representing the five still existing population groups [10]
For contact calls the second axis showed the strongest correlation with differences in highest and lowest frequencies; for alarm calls, call length was most important
Summary
Spatial isolation, diverging environmental conditions and social structures may lead to the differentiation of various traits, e.g. molecules, morphology and behaviour. With this model species we test for potential effects of geographic isolation, diverging altitudes, and social structures. Diverging environmental conditions may drive the isolation of populations [2] Both drivers may lead to the differentiation of taxa, at molecular, morphological and behavioural level [1, 2]. The interplay of both forces, geographic isolation and diverging environmental conditions, Traits involved in communication, such as vocalisations are assumed to be under strong selection [3]. Bird vocalisations have an important function in intraspecific communication and may be used to hold contact to other members within a
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