Temporal variation in a savanna bird assemblage : what changes over 5 years?

Tropical savanna environments are characterised by annual and decadal patterns of resource change, which can affect the patterning of mobile fauna such as birds. In this study, we sampled 60 sites in northern Queensland, four times from 2004 to 2008. We investigated how the bird richness and abundance, and species turnover changed over the sample years and how this differed with vegetation structure. The mean abundance per site was highest in 2005 (92.1±12.0 individuals ha-1) and lowest in 2008 (46.6±3.3), whereas species richness per site was highest in 2004 (19.6±0.9 species ha-1) and lowest again in 2008 (14.7±0.8). Nine species were most abundant in 2004 coincident with extremely high rainfall preceding the survey in that year. Species turnover increased across all sites from 2004 to 2008 and the abundance of 13 species was best accounted for by differences in vegetation structure. Our study demonstrates that local bird communities in the semi-arid fringe of savannas can change rapidly, and mostly where vegetation is modified. This suggests that increased land-use and climate change in northern Australia could have significant effects on the avifauna over fairly short periods.