Relating climatic dynamics in time and space to ecological responses, with application to Australian waterbirds

Many animals move in response to climatic variations, with responses of highly mobile species such as waterbirds being especially dynamic. Climatic patterns are commonly quantified through static aggregation of meteorological variables, yet static analyses may only poorly relate to dynamic ecological responses. A technique is developed here to examine relationships between ecological responses and climatic dynamics through quantifying the dynamic structure of large-scale weather systems as they propagate through time and space. Analyses of localized climatic dynamics permit insight into the dependence of ecosystem responses not just upon spatial and temporal scales, but also upon frequencies and prevailing directions, of climatic variation. The technique is applied to the single variable of the aggregate abundance of all species of waterbirds counted in the annual Eastern Australian Aerial Waterbird Survey. The strongest climatic influence on avian abundance is shown to be the coherence of large-scale precipitation systems with spectral frequencies of around 15 days that propagate south-east into the interior of the continent from the tropical north. Directly aggregated rainfall presents a secondary influence. These comprehensively integrative analyses of localized weather are ultimately able to explain over 75 of the inter-annual variance in the aggregate abundance of over 90 species of waterbirds. These results provide a powerful demonstration of the techniques developed here, and reveal the profound extent to which environmental variability structures Australian ecosystems.