Hypothermic tolerance in an embryonic American kestrel (Falco sparverius)
Embryos of several bird species tolerate acute hypothermia. However, the extent to which it can be tolerated by wild species living under natural conditions is poorly documented. At a single American kestrel (Falco sparverius) nest 15 days into incubation, we observed a 21-h bout of egg neglect by the parents during which nest (egg) temperature averaged 12.7°C. Normal incubation patterns resumed thereafter, and one of three viable eggs hatched 32 days after incubation onset, an incubation period 2.5 days longer than the mean in this study. The nestling appeared to develop and fledge normally. Although embryonic tolerance of extended hypothermia is known to occur in some seabirds, its presence in Falconiformes has not heretofore been recorded. Embryonic hypothermic tolerance may be adaptive in species with extended periods of parental absence during incubation.