Reproductive Correlates of Breeding‐Site Fidelity in Bobolinks (Dolichonyx Oryzivorus)

Abstract

To investigate the relationship between reproductive success (RS) and breeding—site fidelity in a transequatorial migrant, we studied two populations of marked Bobolinks (Dolichonyx oryzivorus) in upstate New York during 1982—1985. At these sites, 44% of the males and 25% of the females resident in one year returned in one or more subsequent years. There were more nests built, eggs laid, eggs hatched, and young fledged in territories of returning males in this polygynous species than in territories of males that did not return in subsequent years (P < .04). For females that returned, the number of eggs hatched, young fledged, young fledged on last nest attempt, and young fledged per egg laid were higher than for females that did not return (P < .02). Discriminant function analysis and data from 1982—1984 were used to predict correctly the return behavior of 30 to 42 individuals (sexes combined) in 1985, based on their reproductive success (RS) in 1984 (P < .01). Using data on RS and return rate for all years, the best single—variable model for males based on the number of young fledged from each territory classified correctly 59 of 85 individuals (69%) as returning or not (P < .005). The best single—variable model for females based on the number of yound fledged on their last nest attempt classified correctly 61 of 86 individuals (71%; P < .005). Using all data for 1982—1985, sex—specific models that included only whether an individual fledged one or more young classified correctly the same proportion as the best single—variable models above. However, among males that fledged one or more young, those that returned had fledged significantly more young the previous year than those that did not return (P < 0.5). Not all individuals that failed to return were dead, because five individuals that did not return to our study sites were captured in a subsequent year at another site. We concluded that male and female Bobolinks used information on their breeding success in one year to influence their choice of breeding site in the next year.