Food-niche Relationships Between Great Horned Owls and Common Barn-Owls in Eastern Washington

organs. There are only two serious limitations to using feather pulp for electrophoretic analysis. First, the birds must either be molting when sampled or be subjected to plucking to stimulate feather regrowth and then recaptured at a later date. Second, in small birds such as Bobolinks, warblers (Parulidae), or chickadees (Parus spp.), only tiny amounts of tissue can be obtained from the flight and tail feathers, necessitating the use of two or more feathers. Mengden and Stock (!976) point out, however, that small quantities of tissue may be put into cell culture to increase the amount available; such tissue cultures may also be stored for indefinite periods of time. Alternatively, other forms of electrophoresis that require smaller quantities of tissue (e.g. cellulose acetate) may be performed when only a few loci need to be examined. Especially useful to field workers, the tissue is conveniently "pre-packaged," and may be placed, whole or with the upper shaft removed, directly onto dry ice or into a portable liquid nitrogen flask. In terms of ease of sample collection and minimization of stress to birds, we suggest that feather pulp is a viable alternative tissue for non-destructive sampling in avian electrophoretic studies. We are grateful to Steven Bloom, Irene Brown, Mike Denison, Tom Gavin, Josh Hamilton, and Jerry Wald~ vogel for their help in obtaining the birds. Scott Camazine and Paul Sherman made many helpful comments on earlier drafts of the manuscript. Funding was provided in part by a Sigma Xi Grant-in-Aid of Research to J. E. Marsden. This work was performed in the Cornell Laboratory for Ecological and Evolutionary Genetics.