ARE AVIAN HEMATOCRITS INDICATIVE OF CONDITION - AMERICAN KESTRELS AS A MODEL

Diseased animals or those in poor condition are known to have reduced hematocrits. Many investigators have assumed that hematocrit levels th us reflect condition and disease status of an animal. This study teste d these assumptions by examining the relation between hematocrits of A merican kestrels (Falco sparverius) during several stages of the breed ing season, and condition, prey abundance, and blood parasite load. We also examined the potential effects of a number of intrinsic and extr insic influences on hematocrit. Hematocrits did not differ between the sexes, or between the pre-laying and incubation periods. Among female s, hematocrit did not vary with the date of sampling, breeding chronol ogy, prey abundance, condition, age, or molt, although hematocrit incr eased with ambient temperature during incubation. Hematocrit of males was not related to breeding chronology prey abundance, condition, age, or molt. During incubation, male hematocrit increased with the date o f sampling and ambient temperature. Hematocrits of both sexes declined with the time of day that the sample was taken, and increased with th e level of infection of the blood parasite Haemoproteus. The use of he matocrits to assess the health and condition of clinically normal kest rels is therefore questionable, and given the positive association wit h parasite loads, may even lead to erroneous conclusions.