Community ecology of mangrove birds

Abstract

The community ecology of birds in mangrove forests at 13 sites in the Darwin region was investigated between February 2008 and April 2009. This study examines the environmental determinants of the community ecology of mangrove birds. A total of 115 bird species representing 43 families were observed. Excluding non-target species, 70 species were recorded at a density of 11.7 ind.ha-1 with eleven mangrove specialists. Large continuous mangrove patches supported fewer species than a combination of several smaller patches. The composition of patches did not comprise nested subsets of bird species, partly because of a seasonal influx from the matrix but also because bird species richness of mangrove patches is highly dependent on the type of habitat in the matrix. Patches surrounded by savanna were species poor, while patches that included monsoon rainforest were relatively species rich. The latter clearly indicates that mangroves contain empty niches, are thus not saturated with bird species and that competition for resources does not play a strong role in structuring the bird community. Null model analysis of non-random assemblage structure (nestedness and species co-occurrence) revealed no deterministic structure to the overall mangrove species assemblage. High bird species richness and density in the mangroves was associated with high plant species richness and abundant, widely available food resources. Overall bird density increased with insect abundance, which varied between seasons and mangrove patches. Insect abundance was highest when mangroves were flowering particularly during the flowering peaks of Bruguiera exarislala and Avicennia marina. In general, partitioning of the available foraging niches was limited resulting in the dominance of the bird assemblage by a few species that are generalists (nectar, insects) and occur at high densities. Consideration of the nature, extent and diversity of the surrounding matrices is vital in managing and conserving mangrove bird communities.

Date of Award	2010
Original language	English
Supervisor	Mike Lawes (Supervisor)