The Effects of Site Quality on Breeding-Site Fidelity in Bobolinks

We compared breeding-site fidelity of Bobolinks (Dolichonyx oryzivorus) at two low-quality sites (Bald Hill and Shackelton Point, BH +SP) with that at one high-quality site (Moore Road, MR) in central New York. Yearly density of fledglings at Moore Road was more than six times the density at Bald Hill and Shackelton Point. Furthermore, individual residents fledged 50-70% more young at the high-quality site. At Moore Road, 70% of the males and 49% of the females returned one or more times, compared with 44% of the males and 25% of the females at the low-quality sites. Successful residents (i.e. those fledging one or more young the previous year) were equally likely to return at all sites. However, the return rates of unsuccessful residents were more than three times higher at the high-quality site. Neither overall return rates nor intrasite dispersal of returning residents differed between individuals that had been successful or unsuccessful the previous year at the high-quality site. At the low-quality sites, individuals unsuccessful the previous year were much less likely to return than were successful individuals (55% vs. 19% for males, 41% vs. 9% for females). Those unsuccessful individuals that did return tended to move farther between nest sites than successful individuals. Overall, site productivity was the best predictor of yearly, site-specific return rates. For females (but not for males), individuals that were resident in one or more years previous were more likely to return than were novice residents (47% vs. 20%). Individuals that had nests experimentally destroyed by hay-cropping returned at similar rates to those of naturally unsuccessful residents. We believe that the patterns of breeding-site fidelity in Bobolinks are primarily the result of experience-based choices by the birds and do not simply reflect patterns of mortality. Bobolinks appear to use both their own reproductive success and that of others at their site to influence their decision to return to a breeding site