Variation in Hematocrit and Total Plasma Proteins of Nestling American Kestrels (Falco sparverius) in the Wild

Hematocrits and total plasma proteins were determined at 24 days old for 86 female and 85 male nestling American kestrels (Falco sparverius) from the wild in northern Saskatchewan. No sex differences were detected in either hematocrit or plasma protein. For females, hematocrit and plasma protein were not related to time of sampling, temperature at sampling, mass of nestlings or length of the tenth primary flight feather. In males, hematocrit correlated only with the length of tenth primary. For both sexes, concentrations of plasma protein declined as the season progressed. Differences in brood size, natural and experimental, did not affect hematocrit or plasma protein levels. Of six nestlings that died before leaving the nest, three showed depressed hematocrit values compared with those that successfully left the nest, whereas none showed significant deviations in plasma protein levels. For 42 birds, we took a second blood sample 2–5 days after the first. Changes in blood parameters of males between these sampling periods were not related to changes in weight, growth of tenth primary or changes in temperature. Among females, there were trends for changes in weight to be correlated with changes in both hematocrit and plasma protein. Our results suggest that hematocrits and plasma proteins of nestling kestrels are not robust indicators of nutritional status and condition. comp biochem physiol 117A; 3:383–390, 1997.  1997 Elsevier Science Inc.