Summary
We describe a technique and apparatus for extracting blood samples from birds in the field. We tested the effect of our technique on the health and behavior of captive Brown-headed Cowbirds (Molothrus ater) and free-living Red-winged Blackbirds (Agelaius phoeniceus). We found that captive Brown-headed Cowbirds that had been bled did not lose any more weight than birds that had not been bled. Territory loss by male Red-winged Blackbirds was not affected by taking blood samples, nor was annual return rate. Female Red-winged Blackbirds that were bled did not differ significantly in their rate of nest aban- donment, nest success, fledging rate or annual return relative to females that were not bled. We conclude that blood sampling is not obviously harmful to wild birds as long as proper precautions are taken. Given the ease of the field technique and the vast potential for information to be gained, field ornithologists should not preclude adding laboratory blood analyses to their research program because of concerns about the technique negatively affecting the birds' health or beh