Annual profiles of blood packed cell volumes of captive American kestrels

Abstract

Mean hematocrits of 20 pairs of captive American kestrels (Falco sparverius) sampled from November 1980 to September 1981 fell significantly (p < 0.0001) from winter maxima of 47.9% for females and 50.9% for males to summer minima of 29.1% for females and 30.1% for males. It is suggested that ambient temperature, reproduction, and molt influence the photoperiodic control of avian hematocrit. Mean hematocrits declined 1–2 months before the onset of molt or egg laying (whichever came first for females) and increased at the termination of molt for nonlaying females only. During nonreproductive and nonmolting states, hematocrits varied indirectly and logarithmically with air temperature (r²_♂+♀ = 0.74) and directly and linearly with body weight (r²_♂ = 0.91, r²_♀ = 0.95). Total mean packed cell volumes of males and females were not significantly different.