Effect of handling time and repeated sampling on avian white blood cell counts

The practice of obtaining white blood cell (leukocyte) profiles and heterophil/lymphocyre (H/L) ratios from avian blood smears has become increasingly popular to assess immune function in wild birds. I captured 28 House Finches (Carpodacus mexicanus) and made blood smears from samples obtained from them at 3, 30, and 60 min after capture to evaluate the effect of routine handling time on leukocyte profiles and H/L ratios. Total leukocyte Counts decreased significantly with time, but the proportions of each leukocyte type remained the same over the 1-h time period. There was a nonsignificant increase in H/L ratios over lime, but comparison with a group of birds held for 1 h before bleeding Suggested that this was the result of the repeated bleedings, not handling time. I conclude that researchers should make every effort to obtain blood samples for making smears as soon as possible after capturing birds to ensure an accurate assessment of total leukocyte counts, but that routine handling times under 1 h do not affect H/L ratios.