Tim Birkhead, Jens-Kjeld Jensen, Jamie Thompson, Sjurdur Hammer, Paul Thompson and Robert Montgomerie

Abstract Members of the seabird family Procellariidae (albatrosses, petrels and shearwaters) typically produce a single-egg clutch. Two-egg clutches have been recorded occasionally in some of those species, but it is not known whether they were laid by a single female. In this study we examine


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