Influence of landscape structure and forest age on the richness and abundance of different bird feeding guilds and forest-dependent birds in a seasonal dry tropical forest of Yucatan, Mexico

Tropical dry forests (TDF) are subject to intense human intervention leading to an increase of secondary forests and changes in habitat suitability for birds. Despite the increasing research on secondary forests, we have little understanding of how such changes in tropical dry forests have affected animal communities. The main goal of this research was to investigate the influence of successional age, vegetation structure, and landscape characteristics on tropical bird species or functional groups (i.e. feeding guilds, forest-dependent birds, and individual species of conservation interest) in a TDF. Specifically, we addressed the following questions for both the breeding season and for the non-breeding season: (1) do different successional stages (age) support different levels of total bird species richness and of species richness of different feeding guilds and the group of forest-dependent bird species; (2) does the relative abundance of individual bird species of conservation interest differ across successional stages, and, (3) what is the relative contribution of succession age, vegetation physical structure, and configuration of landscape elements on the species richness of various feeding guilds and the group of forest-dependent birds, and on the relative abundance of individual species of conservation interest? We used a stratified sampling design based on 274 sites that varied according to successional stages over an area of 352 km(2) in Yucatan, Mexico to assess bird numbers during 2008 and 2009 using the double-observer method. We used a SPOT5 imagery (2005) to produce a land cover map in which the vegetation classes represented different stages of forest succession as well as topographic position. From the land cover map several landscape metrics were calculated and used to relate bird species richness in the different feeding guilds, as well as the relative abundance of the individual species of conservation interest, with landscape structure. We detected 103 species of birds, which were assigned to one of nine feeding guilds and forest-dependent group. Bird species richness was often similar across the successional gradient with guilds changing across the gradient. Specifically, forest age was associated with an increase in species richness of guilds vulnerable to habitat modification and forest-dependent species. Our findings indicate that large, preferably interconnected, patches of older successional forest could aid bird conservation in TDF.