Distribution patterns of birds and insect prey in a tropical riparian forest

Abstract

Spatial subsidies of energy and nutrients can influence the distribution of consumers in riparian habitats. This study compared the abundance and composition of bird assemblages and the availability of volant insect prey within the riparian zone (≤ 30 m from the stream) and further inland (100-250 m away) within a secondary forest in monsoonal Hong Kong. Replicated point-counts of birds and insect light trapping were conducted in each zone during the wet and dry season of 2006-2007. The biomass of adult aquatic insects in the riparian zone was nine to 12 times higher than inland during both seasons, however, total insect biomass (aquatic plus terrestrial insects) in the riparian zone was only 49 percent (wet season) and 18 percent (dry season) greater. More birds (both numbers of individuals and species) were recorded in the riparian zone, and this difference was particularly conspicuous during the wet season. Most of the wet-season difference was due to the greater number of insectivorous birds in the riparian zone (123% greater than inland), and may have reflected the relative availability of adult aquatic insects. These findings confirm the importance of riparian zones as feeding habitats for forest birds, and have implications for conservation planning and setting the boundaries of protected areas. © 2008 The Author(s).