Survival and breeding philopatry in Barrow's and Common Goldeneyes

Adults of many species of birds exhibit considerable fidelity to their previous breeding area (breeding philopatry) and may even use the same nest site in successive years. In many species of birds, breeding philopatry is male-biased (Greenwood 1980). Waterfowl differ from this pattern in that breeding philopatry is female-biased (Greenwood 1980, Lessells 1985), although it is not clear whether this pattern is ubiquitous among the Anatidae. Studies of breeding dispersal are necessary to understand the reproductive consequences of sexbiased philopatry, and also have implications for studies of gene flow and population dynamics (Geramita and Cooke 1982). If breeding philopatry is femalebiased, information on return rates of females with known reproductive histories can provide insight into the costs of reproduction (e.g., Dow and Fredga 1984, Lessells 1986). To date, there have been few attempts to compare patterns of philopatry between areas, and few long-term studies of individually marked birds, although such studies are necessary to test current theories of breeding dispersal (e.g., Greenwood 1980). It has therefore been difficult to separate the influence of life history variation from the effects of environmental variability (Harvey et al. 1984). Finally, there has been no test of the reliability of the methods used to detect dispersal. For example, most estimates of philopatry in waterfowl are based on recaptures of females on their nests, usually late into incubation (e.g., Nilsson 1971, Dow and Fredga 1983, Hepp et al. 1987). Such methods would underestimate survival and philopatry because females that returned to their breeding area, but did not nest successfully, would be missed. The sample of philopatric females would be biased in favor of successful birds.