Altitudinal patterns in the population ecology of mountain bird species are useful for predicting species occurrence and behavior. Numerous hypotheses about the complex interactions among environmental factors have been proposed; however, these remain controversial. This study investigated the causes of altitudinal patterns in breeding bird species richness and density in relation to climate, habitat heterogeneity, and migration influence in Jirisan National Park, South Korea. We conducted a field survey of 142 plots at altitudes between 200 and 1400 m above mean sea level in the breeding season. A total of 2771 individuals from 53 breeding bird species were recorded. Altitudinal patterns of species richness and density showed a hump-shaped pattern, indicating that the highest richness and density could be observed at moderate altitudes. Models constructed with 16 combinations of six variables demonstrated that species richness was positively correlated with vertical and horizontal habitat heterogeneity, and that density was positively correlated with vertical, but not horizontal, habitat heterogeneity, and negatively correlated with migrant rate. No significant relationships were found between spring temperature and species richness or density. Therefore, the observed patterns in species richness support the hypothesis that habitat heterogeneity, rather than climate, is the main driver of species richness. And neither habitat heterogeneity nor climate hypotheses fully explains the observed patterns in density. However, vertical habitat heterogeneity does likely help explain observed patterns in density. The heterospecific attraction hypothesis did not apply to the distribution of birds along the altitudinal gradient. Appropriate management of vertical habitat heterogeneity, such as vegetation cover, should be maintained for the conservation of bird diversity in this area.
Bird species richness patterns of northern Taiwan: primary productivity, human population density, and habitat heterogeneity
