HUNT, J.A.; KAISER, S.A.; VLECK, D.; VLECK, C.M.: Heterophil and lymphocyte cell ratios and plasma creatine kinase activity in passerines during migration

Little is known about condition of birds undergoing seasonal migrations between the breeding and wintering grounds. Condition during migration will presumably affect their survival and success at their destination. We mist-netted birds at a stop-over site in central Iowa during spring and fall migration, and banded, weighed and measured them. We took blood samples from 17 common yellowthroats (Geothlypis trichas), 19 ovenbirds (Seiurus aurocapillus), 28 red-eyed vireos (Vireo olivaceus), 44 Swainson’s thrushes (Catharus ustulatus), and 17 white-throated sparrows (Zonotrichia albicollis). Hematocrit and sedimentation rate in whole blood, and the plasma creatine kinase (CK) activity were measured in most samples. We made blood smears and counted the ratio of heterophils to lymphocytes as an indicator of general stress. Heterophil-lymphocyte ratios (H/L) were transformed using the arcsine transform. There were no significant differences in H/L between species (p = 0.10), although the ratio tended to be higher in the common yellowthroats than in the other species. H/L ratios also did not vary across the season or between seasons. H/L ratios did not vary with hematocrit, subcutaneous fat deposits, sedimentation rate or body mass within a species, however H/L ratio increased with CK (p = 0.007). Elevated CK activity is thought to be an indicator of muscle damage. The phagocytic heterophil population routinely increases during inflammation, whereas lymphocyte counts decrease with infection and stress. Those birds with elevated values for H/L and CK may be suffering injury or muscle damage associated with the flight that could hinder their ability to survive migration.