U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

January 1989


The Condor 91:242-253 The Cooper Ornithological Society 1989. Permission to use.


Dispersal resulting in gene flow strongly affects the evolution of genetic structure in populations. This report describes statistical estimators of dispersal parameters based on USFWS banding recovery records. Finite-area studies of avian species yield estimates of root-mean-square (RMS) dispersal along a transect of about 1 km per generation. In contrast, estimates of RMS dispersal for the Red-winged Blackbird (Agelaiusp hoeniceus) and Common Grackle (Ouiscalus auiscula), based on USFWS banding recovery records, are 94.6 and 111.4 km per generation, respectively. Distributions for both species are extremely leptokurtic, and confidence intervals based on jackknife statistics are large because the estimators are sensitive to outlying values. Dispersal rates can also be estimated from gene frequency data. Although all three kinds of data are not available for any one avian species, genetic-based estimates for several species are consistent with our estimates for Red-winged Blackbirds and Common Grackles in inferring that gene flow is generally high in North American birds-probably closer to 100 km than 1 km per generation. High gene flow also implies that where geographic variation is observed, such as plumage patterns across hybrid zones, selection plays a role in maintaining the pattern of geographic variation.
Key words:
Avian dispersal
gene flow
population genetics
hybrid one
Red- winged Blackbird
Common Grackle.