Tree-cover gradients modulate the taxonomic and functional diversity of birds in Amazonian cattle-ranching landscapes

Cattle-ranching expansion is a major anthropogenic driver of forest transformation in the Colombian Amazon. Landscapes characterized by low ecological connectivity and simplified arboreal structure constrain resource availability and reshape avian community composition and functional trait distributions. We examined the relationship between taxonomic and functional diversity of bird assemblages along a landscape-scale tree-cover gradient, encompassing four cover categories—open (OP), semi-open (SO), semi-closed (SC), and closed (CL)—based on 491-point counts conducted across 104 cattle-ranching mosaics in the northwestern Colombian Amazon. A functional trait matrix was compiled for 342 species grouped into four trophic guilds. Taxonomic diversity indices (Margalef, Shannon, Simpson) and five multidimensional indices of alpha functional diversity were calculated, and correlations between taxonomic and functional metrics were assessed by guild and cover type. The tree-cover gradient modulated patterns of richness, evenness, and functional structure in a guild-specific manner. In open and semi-open covers, insectivores exhibited higher functional richness associated with traits suited to foraging in simplified habitats, whereas intermediate covers supported greater evenness and functional complementarity among frugivores and granivores. In closed covers, correlations between taxonomic and functional dimensions suggest stronger environmental filtering and functional convergence rather than reductions in mean diversity values. Overall patterns are consistent with metacommunity dynamics, in which local assemblages and cross-habitat spillover contribute to maintaining functional diversity at the mosaic scale. From a management perspective, reducing habitat contrast and enhancing structural connectivity within cattle-ranching landscapes may help sustain avian diversity and the functional potential of bird communities in the Colombian Amazon.