Stress responsiveness in nestlings: A comparison of two sampling techniques

Abstract

I compared the effects on plasmacorticosterone levels of twomethods of collecting blood samples during standardized capture-and-handling stress protocols. In one method, individual nestling American Kestrels (Falco sparverius) were bled three times: when initially removed from the nest, and 15 and 30 min later. In the other method, siblings removed from a nest were bled once each, either at the time of removal, or 15 or 30 min later. I found no difference between the two groups in plasma corticosterone levels at the first sampling time, but 15 and 30 min after capture the singly bled birds had significantly higher plasma corticosterone levels than the multiply bled birds. The results suggest that data from multiply bled birds underestimate actual circulating hormone levels. The underlying mechanism for this phenomenon is unknown, but it may involve hemodilution. © The American Ornithologists' Union, 2008.