Niche partitioning among three tree-climbing bird species in subtropical mountain forest sites with different human...

Closely related and ecologically similar species that overlap in ranges can coexist through resource partitioning without one pushing the others to extinction through competition. Understanding resource partitioning among species is essential to predicting how species decline can affect the functioning of communities and ecosystems. In this study, we analyzed niche overlap and resource partitioning of three tree-climbing bird species in disturbed and undisturbed forest sites at La Malinche National Park, Tlaxcala, Mexico. From January to December 2008, resource partitioning between the three species was examined through the frequency of sightings of individuals foraging in different sites in the trees of both forest types. We characterized the pattern of resource utilization by niche breadth and niche overlap. Finally, we tested if these birds divide tree space differentially according to forest type.

Our results indicate that in undisturbed sites, pygmy nuthatches had a high niche breadth (foraging significantly more on the thin branches), while white-breasted nuthatches and brown creepers had similar medium niche breadth values (more often foraged in thick branches and lower trunk, respectively), causing the last two to have a high niche overlap. In contrast, in disturbed sites, niche breadth and overlap values were similar for all three tree-climbing species. All observed overlaps for both forest types were higher than expected, but expected values in disturbed sites suggest the possibility of competition on these sites. Pygmy nuthatches were more sighted than white-breasted nuthatches and brown creepers in both forest types.

Our study shows that differences in tree use suggest resource partitioning among the three bird species, particularly at undisturbed sites. However, activities of excessive logging and grazing in the disturbed sites resulted in niche overlap among species. This could lead to changes in competitive dynamics among them.