Four cases of inbreeding in a small population of the Snowy Plover

Close inbreeding has increasingly been reported from wild and captive populations of vertebrates, often with fitness consequences that are especially problematic for the viability of threatened/endangered taxa. Over 11 years, we observed four instances of close inbreeding (i.e., social pairings between: father–daughter, siblings, mother–son, and grandmother–grandson) in a small, geographically isolated population of the Snowy Plover Charadrius nivosus. These four  cases run the gamut of kin recognition by individuals involved (i.e., males care for offspring; siblings reared together; females abandon males to care of young shortly after hatch; grandparents rarely associate with kin other than in winter flocks). In each case, the pairing between close kin occurred when the population was at or near its lowest and under circumstances where individuals had established themselves at isolated breeding sites such that pairing between close kin was even more likely. In two instances, the inbred pairs fledged offspring; however, the mother–son pairing yielded a 3-egg clutch in which embryos showed no sign of development.