Environmental factors drive habitat partitioning in birds feeding in intertidal flats: implications for conservation
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We present data on the low-tide distribution of shorebirds in the Tagus estuary, Portugal, and relate the distribution of the bird assemblage with environmental factors. The study was based on an extensive survey of the majority of the intertidal flats, carried out with a high spatial resolution. The environmental factors that mostly affected the distribution of shorebirds were the exposure period, the type of sediment and the extent of the shell banks. The feeding bird assemblage could be divided into four main groups of species, and these occupied distinct areas of the estuary. These findings imply that maintaining the overall value of the estuaries for foraging shorebirds requires relatively extensive intertidal areas, encompassing sediment flats with the large diversity of ecological characteristics required by different species.
KeywordsCanonical correspondence analysis Low-tide counts Shorebird Spatial distribution Tagus estuary
We thank the many volunteers who provided assistance during fieldwork. We are particularly grateful to Ana Tavares, Ricardo C. Martins and Susana L. Rosa for their continuing support. Two anonymous referees offered useful and constructive comments. This work was funded by Fundação para a Ciência e a Tecnologia, through research projects Sat-Tagis (Contract POCTI/C/MAR/15256/1999) and Pred-Tagis (POCTI/POCTI/BSE/47569/2002), both co-financed by the ERDF and grant SFRH/BPD/11544/2002 to JPG.
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