Habitat effects on chick-a-dee call complexity
Past studies on the communication systems of species in urban environments (such as Common Starlings (Sturnus vulgaris), nightingales (Luscinia megarhynchos Brehm), brown-headed cowbirds ( Molothrus ater), Southern brown tree frogs (Litoria ewingii )) have shown multiple ways that species change vocal signaling behavior to adjust to urban habitats (e.g. alarm calls and singing). This study further investigates the changes in signaling in relation to the chick-a-dee call of the Carolina chickadee (Poecile carolinensis). A secondary goal of this study was to compare both the amount of information and rate of calling across seasons. Six different variants of chick-a-dee calls were used in playbacks at sites in three types of habitats: closed canopy, mixed and urban. Ad lib recordings were also conducted around the area. Playback trials and ad lib recordings overlapped both the breeding and the non-breeding season to facilitate observations of seasonal changes. The recordings were analyzed for seasonal and habitat differences in call rate, information encoded in call and notes, average call length, and probability of note transitions. Our results show that chick-a-dee rates differed significantly between treatments and seasons suggesting seasonality in the context of the calls. Across the habitat types, we found indications of increased vocal complexity in closed canopy flocks. Vocal response rates and distance of approach in these closed forest flocks differed significantly between playbacks compared to the other habitats. In urban habitats there was no difference between responses to the treatments suggesting less vocal complexity. Based on our results, habitat as well as season seems to create additional complexity in the chick-a-dee call system.
Lucas, Purdue University.
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