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 f or 86 female and 85 male nestling American kestrels (Falco sparverius) from the wild in northern Saskatchewan. No sex differences were detec ted in either hematocrit or plasma protein. For females, hematocrit an d plasma protein were not related to time of sampling, temperature at sampling, mass of nestlings or length of the tenth primary flight feat her. In males, hematocrit correlated only with the length of tenth pri mary. For both sexes, concentrations of plasma protein declined as the season progressed. Differences in brood size, natural and experimenta l, did not affect hematocrit or plasma protein levels. Of six nestling s that died before leaving the nest, three showed depressed hematocrit values compared with those that successfully left the nest, whereas n one showed significant deviations in plasma protein levels. For 42 bir ds, we took a second blood sample 2-5 days after the first. Changes in brood parameters of males between these sampling periods were not rel ated to changes in weight, growth of tenth primary or changes in tempe rature. Among females, there were trends for changes in weight to be c orrelated with changes in both hematocrit and plasma protein. Our resu lts suggest that hematocrits and plasma proteins of nestling kestrels are not robust indicators of nutritional status and condition. (C) 199 1 Elsevier Science Inc.