Bald Eagle

Santa Catalina Island, California

In 1980, the U.S. Fish and Wildlife Service and the Institute for Wildlife Studies (IWS), with the cooperation of the California Department of Fish and Game and the Santa Catalina Island Conservancy, initiated a program to reintroduce bald eagles to Catalina Island. Between 1980 and 1986, 33 eagles were collected from wild nests and released from three different artificial nest or "hacking" platforms on Catalina Island (Garcelon 1988). Once the birds were able to fly (at around 12 weeks of age) the doors were opened on the towers and the young eagles were free to explore the island. Many of these birds matured and formed breeding pairs on the island. The first eggs were laid in 1987, but unfortunately they broke soon after they were laid. Concentrations of DDE (a metabolite of DDT) in the remains of eggs removed from failed nests implicated this contaminant as the causal agent of the lack of productivity (Garcelon et al. 1989), as DDE levels had been found to be inversely correlated with productivity in previous bald eagle studies (Wiemeyer et al. 1984). During 1991-93, IWS studied food habits of the released eagles and documented high levels of DDE in the tissues of certain prey items commonly consumed by these eagles (Garcelon 1997, Garcelon et al. 1997a,b).

Since 1989, the reintroduced population has been maintained through manipulations of eggs and chicks at each nest site and through additional hacking of birds. Because of the high DDE concentrations in the eggs, this active program of manipulation and augmentation is the only way to maintain the Catalina Island bald eagle population at this time. In the egg manipulation process, structurally deficient eggs laid by the birds affected by DDE are replaced with artificial eggs, with biologists often using extreme measures (including helicopter lifts) to reach remote nest sites. The adult eagles continue to incubate the artificial eggs while the real eggs are relocated and artificially incubated at our incubation facility on Catalina Island. Chicks that hatch from these removed eggs, or those produced by captive adults at the ACC or by wild birds, are then fostered back into the nests. Since 1989, 38 chicks have been successfully fostered into nests on Catalina Island and two healthy eggs placed in nests have hatched and the chicks successfully reared. Continued hacking activities have also resulted in the release of an additional 21 eagles since 1991.

Previous studies have documented the effects of pesticides (including DDT and DDE) on the reproductive behavior of avian species (Peakall and Peakall 1973, Haegele and Hudson 1977, Tori and Peterle 1983). Behavioral abnormalities observed in captive and wild birds have included less aggressive nest defense (Fyfe et al. 1976), increase in the length of courtship behavior (Tori and Peterle 1983), and erratic incubation behavior (Peakall and Peakall 1973). Given the extremely high concentrations of DDE found in blood and other tissues collected on Catalina Island (Garcelon 1997), it is important to determine if these eagles exhibit aberrant behavior and to identify prey items. To accomplish this we view some nests using closed-circuit video systems, while other nests are observed from concealed blinds. Once the birds fledge (leave the nest) at about 12 weeks of age, biologists monitor the immature birds' movements around the island to ensure they are healthy and finding food. Many young birds leave the island in the late summer of their first year and have been seen at various locations from southern California to British Columbia. These birds may return to Catalina Island when they reach breeding age (about 4-5 years old) to establish a breeding territory. Other young birds remain on Catalina and move about the island for several years before settling down in a territory. Through our efforts there are now 6 breeding pairs and an average of 4-6 younger eagles residing on Catalina Island.

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Literature Cited

  • Garcelon, D.K. 1988. The reintroduction of bald eagles on Santa Catalina Island, California. M.S. thesis, Humboldt State University, Arcata, CA. 58 p.

  • Garcelon, D.K. 1997. Effects of organochlorine contaminants on bald eagle reproduction at Santa Catalina Island. Expert Report submitted to the Damage Assessment Office, U.S.Fish and Wildlife Service, Sacramento Field Office, California. 16 p.

  • Garcelon, D.K., J.S. Romsos, and P. Golightly. 1997a. Food habits of bald eagles on Santa Catalina Island, January-July 1993. Unpub. report submitted to the Damage Assessment office, U.S. Fish and Wildlife Service, Sacramento Field Office, California. 20 p.

  • Garcelon, D.K., S. Tomassi, D. Kristan, and D. Delaney. 1997b. Food habits of the bald eagle on Santa Catalina Island, November 1991 - December 1992. Report submitted to the Damage Assessment Office, U.S. Fish and Wildlife Service, Sacramento Field Office, California. 24 p.

  • Haegele, M. A. and R. H. Hudson. 1977. Reduction of courtship behavior induced by DDE in male ringed turtle doves. Wilson Bulletin 89:593-601.

  • Peakall, D.B. and M.L. Peakall. 1973. Effect of a polychlorinated biphenyl on the reproduction of artificially and naturally incubated dove eggs. Journal of Applied Ecology 10:863-868.

  • Tori, G.M. and T.J. Peterle. 1983. Effects of PCBs on Mourning Dove courtship behavior. Bulletin of Environmental Contamination and Toxicology 30:44-49.

  • Wiemeyer, S. N., T. G. Lamont, C. M. Bunck, C. R. Sindelar, F. J. Gramlich, J. D. Fraser, and M. A. Byrd. 1984. Organochlorine pesticide, polychlorobiphenyl, and mercury residues in bald eagle eggs — 1969-1979 — and their relationships to shell thinning and reproduction. Archives of Environmental Contamination and Toxicology 13:529-549