Annual Survival Rates of Wintering Sparrows: Assessing Demographic Consequences of Migration

Abstract

AbstractThe demographic consequences of migration have important implications for both evolutionary ecology and conservation biology. We investigated local survival rates for six populations of sparrows at a wintering site. Recent developments in mark–recapture statistics were applied to a 13 year dataset with large numbers of marked individuals (n = 1,632 to 4,394). The study taxa were closely related, and included one resident species (Song Sparrow [Melospiza melodia gouldii]), one short-distance migrant (“Puget Sound” White-crowned Sparrow [Zonotrichia leucophrys pugetensis]), two moderate-distance migrants (Lincoln's [Melospiza lincolnii] and Fox [Passerella iliaca] sparrow), and two long-distance migrants (“Gambel's” White-crowned [Zonotrichia leucophrys gambelii] and Golden-crowned [Zonotrichia atricapilla] sparrow). A literature review demonstrated a cline in fecundity among these sparrows: resident and short-distance migrants laid multiple clutches of few eggs, whereas long-distance migrants tended to produce one large clutch. Annual rates of local survival were low in the interval after first capture (<0.35), possibly because of variation in true survival, site-fidelity, presence of transients and heterogeneity of capture. Estimates of local survival among birds that returned at least once were more robust and were comparable among Song (0.558 ± 0.054 SE), Puget Sound White-crowned (0.461 ± 0.026), Lincoln's (0.456 ± 0.066), Fox (0.352 ± 0.0), Golden-crowned (0.422 ± 0.023) and Gambel's White-crowned (0.432 ± 0.0) sparrows. Estimates of survivorship for Lincoln's and Fox sparrows are among the first values available for those species. Local survival was not higher among resident than migratory taxa, nor did it covary with migration distance among migratory species. These results did not support the time-allocation hypothesis of Greenberg (1980), but are consistent with aspects of bet-hedging theory. While these analyses have potential implications for conservation of migratory birds, further work is required to establish whether these patterns are applicable to Neotropical migrants.