Ardea
Official journal of the Netherlands Ornithologists' Union

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McNeil R., Diaz M.T. & Villeneuve A. (1994) The mystery of shorebird over-summering: A new hypothesis. ARDEA 82 (1): 143-151
Various hypotheses explaining over-summering behaviour (individuals remaining on wintering grounds during the boreal summer) in boreal-breeding shorebirds are summarized. Most over-summering individuals are sexually immature first-year birds, but some adults in a few species over-summer. Among species known to over-summer, many first-year birds do migrate and breed. Why do some individuals, first-year birds and older, over-summer in southern latitudes while other members of the same species and age classes return to the Arctic and breed? In over-summering shorebirds, pre-migratory moult and fattening either do not take place, or are delayed. The possibility of a relationship between trematode infestation and over-summering is suggested. Helminth infestation and acquisition of partial immunity to reinfection would explain at least in part (1) why the shorebird over-summerers are mainly first-year birds, and (2) why the adults also over-summer but in smaller numbers.


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