Total plasma protein level as an indicator of condition in wild American kestrels (Falco sparverius)

Total plasma protein levels were determined for 292 female and 228 male American kestrels (Falco sparverius) in the wild. Plasma protein levels were significantly higher in females than in males, and higher during prelaying than during incubation. For both sexes, plasma protein levels did not vary significantly with the number of days before or after egg laying on which the sample was taken, time of sampling, prey abundance, age, molt, or infection by the blood parasite Haemoproteus sp. Protein levels in females increased with date of sampling and body condition during prelaying, while the same pattern was seen in males during incubation. With the exception of those of prelaying females, plasma protein levels increased with ambient temperature. The results of this study suggest that at least some of the variation observed in total protein levels is attributable to physical condition. However, further investigation is required before the reliability of using total plasma protein level as a tool to assess the health and condition of kestrels is known.