COMPARATIVE FECUNDITY AND SURVIVAL OF BALD EAGLES FLEDGED FROM SUBURBAN AND RURAL NATAL AREAS IN FLORIDA

Abstract

We compared the reproductive biology, dispersal, and subadult survival of bald eagles (Haliaeetus leucocephalus) from nest sites in suburban and rural landscapes in west-central Florida, USA, from 1997 to 2001. We documented the reproductive outcome of randomly selected suburban (n = 60) and rural (n = 60) bald eagle nest attempts. We also used satellite tracking packages on randomly selected rural (n = 35) and suburban (n = 35) bald eagle fledglings. Nest-site occupancy varied among years (range = 75.0–100.0%), but averaged 90% for nests in both land-use categories. The overall mean nesting start date was similar for both groups (suburban = 11 Dec, rural = 13 Dec). Bald eagles occupying nest sites in both land-use categories raised an average of 1.3 young to 8 weeks-of-age, and pairs that fledged ≥1 young raised an average of 1.7 young to 8 weeks-of-age. Most bald eagle fledglings from our study area migrated northward, some as far as Newfoundland, Canada. The core summering area was the Chesapeake Bay and the coastal plain of North Carolina, USA. Successful fledglings started northward migration earlier on average at rural than at suburban nest sites (124 vs. 132 days-of-age). Survival of both groups was similar until dispersal (approx 91%); however, during the first northward migration, mortality of suburban fledglings increased disproportionately. One year after fledging, survival of rural fledglings was 89% compared to 65–72% for suburban fledglings. Survival of the 2 groups was similar (84–90%) thereafter. Suburban bald eagles died more often from anthropogenic factors (primarily electrocution and vehicle collision) than rural bald eagles, though most of these deaths occurred in rural areas after dispersal from natal areas. We suggest that suburban bald eagle fledglings were more acclimated to dangerous anthropogenic landscape features than rural eagles, and as such did not regard them with the same degree of caution. Despite the difference in first-year mortality, population models suggest that both groups are experiencing positive population growth rates.