Bird song changes sound alarm over habitat fragmentation

Changes in bird song could be used as an early warning system to detect man-made ecological disturbances, new research published in the British Ecological Society's Journal of Applied Ecology has found. Although much previous research has focused on bird song and vocal mimicry, this is the first study to analyse the role played by habitat loss and fragmentation on song-matching.

Ecologists recorded and analysed the songs of more than 200 Dupont's larks, Chersophilus duponti, in Spain and Morocco and found that in fragmented habitats, song-sharing among neighbours was enhanced whereas song-sharing among non-neighbours declined. Having ruled out other explanations, such as the stage of the breeding season and competition intensity, the researchers say this change in song-sharing is due to lack of interaction between individuals isolated by habitat barriers.

According to the study's authors, Dr Paola Laiolo and Dr José Tella of the Estación Biologica de Doñana in Seville, Spain: "We found that habitat loss in the steppe matrix markedly affected song-type sharing mechanisms in Dupont's lark. The occurrence of anthropogenic habitat barriers seems to hinder cultural transmission of song types over distances, resulting in an intensification of the differences between non-neighbours and increasing mimicry between neighbours. This suggests that males from fragmented habitats perceived as rivals only the close neighbours with which they engaged in counter-singing."

"Communication systems of habitat-sensitive species might be used as a behavioural indicator of anthropogenic environmental deterioration. Because of their rapidly evolving cultural nature, bird vocalisations might become an early warning system detecting the effects of fragmentation over relatively short times and before other indicators - such as genetic markers - show any change," they say.

Sharing song types - when a male replies to a rival's song with the same song sequence - with neighbours is common in birds, and is thought to act as a threat signal between males, which would explain why birds have evolved such complex song repertoires.

The Dupont's lark is a rare and specialised steppe passerine, and its song unit is made up of up to 11 discrete sequences, each sequence being composed of up to 13 notes. The most common sequence is known as the 'whee-ur-wheeee'. To be considered as shared songs in this study, two sequences had to match at least 75% of their component notes and the matching portions had to be similar in note shape, timing and frequency.

Source : Blackwell Publishing Ltd.