The Effect of Pine Forest Structure on Bird-Mobbing Behavior: From Individual Response to Community Composition

Abstract

Pine-forest bird communities are affected by the forest structure and the density and composition of its understory vegetation. In this study, we focused on the combined effects of vegetation structure and caller identity on the mobbing behavior of birds in breeding and non-breeding seasons. We examined the effect of the understory structure and the density of three types of conifer forest habitats on bird behavior by broadcasting three different types of mobbing calls: Those of two all-year resident species in the state Israel (Sardinian warbler Sylvia melanocephala Gmelin and great tit Parus major L.) and one European species (coal tit Periparus ater L.), which is absent from these habitats. The mobbing call attracted 689 birds of 17 species, which represented 31% to 95% of the forest bird species that we detected in point counts at the same study plots. Bird reactions to mobbing calls were affected by the status and season, depending on forest type. Our results show that responses were stronger in forests with developed understory in comparison to forests with no understory, especially in winter. The highest number of responders and highest species richness of responders were observed in winter. P. major calls generated more interspecific than intraspecific responses, whereas S. melanocephala calls generated equal levels of inter- and intraspecific reactions. Both species generated different response patterns across the three forest habitat types. The response level of responders is higher when the mobbing calls are issued by local species rather than the P. ater. In winter, the response of non-resident species was higher than of resident species. Based on these results, we encourage the managers to maintain well-established understory vegetation, with special attention to the shrubs layer, to promote species diversity and rich behavioral responses of birds in the conifer forests in the eastern Mediterranean region.