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. Resume : Les embryons de plusieurs especes d'oiseaux sont capables de tolerer une forte hyperthermie. Cependant, l'ampleur de cette tolerance chez des especes sauvages vivant dans des conditions naturelles a ete peu etudiee. Nous avons observe un nid de Crecerelles d'Amerique (Falco sparverius) neglige par les parents pendant une periode de 21 h, 15 jours apres le debut de l'incubation; la temperature des oeufs a ete en moyenne de 12,7°C au cours de cette periode. Les parents se sont remis a couver les oeufs normalement apres ce temps et l'un des trois oeufs viables a eclos apres 32 jours d'incubation, une periode de 2,5 jours de plus que l'incubation moyenne evaluee au cours de cette etude. L'oisillon semble s'etre developpe normalement jusqu'a l'envol. Bien que la tolerance embryonnaire a l'hypothermie soit un phenomene courant chez certains oiseaux marins, ce phenomene n'avait jamais ete observe auparavant chez un Falconiforme. La tolerance des embryons a l'hyporthermie peut etre interpretee comme une adaptation chez les especes qui doivent subir de longues absences des parents au cours de l'incubation. (Traduit par la Redaction) Notes 1402

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