The stability of bird assemblages across time and the reliability of snapshot surveys

Abstract

‘Snapshot’ surveys conducted over 1 year or less are widely used to describe avian community composition. Maron et al. (Austral Ecology, 2005, 30, 383) questioned the utility of snapshot surveys and the conclusions drawn from them following repeat bird surveys at 26 sites in western Victoria, 7 years after initial surveys. They concluded, ‘the distribution of most species did not differ significantly from that expected if species had redistributed at random among sites’. Only five of 54 species recorded in both years had distributions that changed significantly less than expected among sites between the survey periods. We question whether this is the exception rather than the rule for Australian landbird communities in wooded habitats for three reasons: (1) passerine species dominate these communities and tend to remain faithful to a site once a breeding territory has been established; (2) most landbird species are sedentary or migratory, not nomadic; and (3) most Australian passerines are long-lived, so surveys conducted within decadal timeframes may sample the same individuals. We examined the constancy of bird community composition by conducting repeat surveys at 29 sites in two vegetation types in the Namoi Valley, northern New South Wales, 7 years after the first survey. Bird assemblage composition in our study exhibited high levels of turnover between surveys, but 21 of 62 species present in both survey periods were significantly more likely to be found at the same sites in the second period as the first, and the tendency of most species was of site fidelity. Mantel tests demonstrated that assemblage composition at the same sites was more similar than expected by chance. Moderate levels of site fidelity among species and significant levels of assemblage composition constancy among sites should be the expectation when monitoring Australian landbird communities in wooded habitats over extended timeframes, except in the cases of major landscape transformation and extreme climatic disruptions.