Birdsong characteristics are related to fragment size in a neotropical forest

Abstract

The oscine passerines, an avian suborder that comprises almost half of all bird species worldwide, learn their song primarily through cultural transmission. As the world's forests become increasingly fragmented and the population sizes of many forest-dwelling species decline, there may be increasingly restricted opportunities for the transmission of cultural information. However, the effects of forest fragmentation on birdsong have not been well documented. In this paper, we examine the relationship between forest fragment size and song characteristics for two forest bird species, an oscine passerine (orange-billed sparrow, Arremon aurantiirostris) that learns its song culturally, and a suboscine passerine (scale-crested pygmy tyrant, Lophotriccus pileatus) that does not. Recordings were taken from individuals in 12 premontane wet forest fragments ranging in size from approximately 1.4 ha–360 ha in southern Costa Rica. As predicted under the ‘cultural erosion’ hypothesis, we found that acoustic characteristics associated with song complexity such as the number of syllables per song and song duration decreased with decreasing fragment size for the oscine but not for the suboscine species. This study supports the idea that learned cultural elements are sensitive to fragment size and that cultural diversity should be considered along with other forms of biodiversity in the conservation of social learning species.