Abstract

Eagles of the genus Haliaeetus are often referred to as fish or sea eagles because of what they eat and where they live. This close affiliation with aquatic ecosystems along with their large size and often vocal presence make them highly visible and vulnerable to competition for their preferred habitat and food source. They are also susceptible to the bioaccumulative effects of agricultural and industrial pollutants that end up in the water and increase in concentrations in consumers at all levels in the aquatic ecosystem, but have the greatest potential for deleterious effects at the level of this apex consumer. Their precarious position at the top of this complex food web has resulted in all eight of these species being threatened or endangered in at least part of their historic range while they are totally non-existent in many areas that once held numerous sea eagles. There are many programs and funded research projects trying to prevent the further decline and to facilitate the recovery of these impressive and charismatic species. Haliaeetus species seem nearly ideally suited as biomonitors of pollutants in the water and as indicators of the quality of the aquatic ecosystem in general.³ The Swedish Society for Nature Conservation (SNF) undertook an investigation into the population status of white-tailed sea eagles (H. albicilla) in 1964 because of the alarming decline in populations of this once-numerous species all over Europe. In the early 1960s, similar efforts were becoming organized in the Great Lakes ecosystem of North America because of similar declines in bald eagle (H. leucocephalus) populations. In 1971, the SNF launched “Project Sea Eagle,” which helped organize various activities under two main headings: Monitoring and Research, and Conservation and Management. In 1985, the International Joint Commission designated the bald eagle as the indicator species for water quality in the Great Lakes basin of North America,⁴ and the Department of Environmental Quality for the State of Michigan, USA started using bald eagles as a biomonitor for surface water quality and to assess safety of fish consumption by humans in Michigan watersheds. In 1989, the white-tailed sea eagle was chosen as an indicator of effects from chemical pollutants and of environmental health in the Swedish Baltic Coast environment. Monitoring of breeding populations was integrated in the national Swedish Environmental Monitoring Programme (SEMP) under the Swedish Environmental Protection Agency (SEPA), which is currently working on a multifaceted national species action plan which also focuses on causes of mortality and productivity.

Much of these early efforts with H. albicilla and H. leucocephalus went into banding of young in successful nests and evaluating productivity, although eggshells, addled (unhatched) eggs and dead birds were examined. DDE and other metabolites of DDT along with PCBs (polychlorinated biphenyls) were determined to be the main contaminants responsible for population declines. In Michigan, specific toxic reference values were developed by combining concentration data from eggs and blood with reproductive outcome data. Studies showed that bald eagles nesting in coastal areas adjacent to the polluted Great Lakes averaged fewer fledged young per nest than birds nesting on rivers away from the coast, while birds nesting on large rivers eating anadromous fish from the Great Lakes had productivity levels somewhere in between. Blood samples were drawn from nestlings to check for contaminants, and these cause-effect relationships have been proven and critical effect levels have been determined. As populations of bald eagles recover, and they resume nesting in most of their historic range, they are even more useful as biomonitors.¹ They can be used to monitor success of cleanup efforts of known contaminants as well as sentinels for emerging problems with contaminants and diseases.

Many countries have been monitoring and protecting Haliaeetus species for a long time. There are many success stories of recovered populations as well as continued and emerging problems in some species. A major conference, SEA EAGLE 2000, brought many researchers together while celebrating the 30th anniversary of the Swedish Sea Eagle Project. The extent of interest in Haliaeetus species worldwide, along with the excellent book of published proceedings² helped stimulate the formal organization of SEA EAGLE (Systematic Environmental Assessment: Eagles Assess Global and Local Ecosystems) with Michigan researchers organizing initial efforts.

Techniques developed by many researchers handling and sampling bald eagles in Michigan and white-tailed sea eagles in Sweden have proven to be transferable to other Haliaeetus species such as the African fish eagle (H. vocifer) in Uganda and South Africa and Steller’s sea eagle (H. pelagicus) in the Russian Far East.

The goal of SEA EAGLE is to share technology and train people to develop local programs to assure the stability and recovery of all Haliaeetus species worldwide while using them as biomonitors of environmental health. Another goal is to use them and their plight to educate the public on the many and varied influences of human activity that can be understood by research and modified to allow successful recovery and management of these magnificent birds for present and future generations to enjoy. Zoos certainly have an important role in this process of education and appreciation of these species as well as the potential to help raise funds for these management and recovery activities by the judicious use of these charismatic birds in appropriate exhibits.

Literature Cited

1.  Bowerman, W.W., D.A. Best, J.P. Giesy, M.C. Shieldcastle, M.W. Meyer, S. Postupalsky and J.G. Sikarskie. 2003. Association between regional differences in polychlorinated biphenyls and dichlorodiphenyl dichloroethylene in blood of nestling bald eagles and reproductive productivity. Environ. Toxicol. Chem. 22:371–376.

2.  Helander, B., M. Marquess, and W. Bowerman (eds.). 2003. SEA EAGLE 2000. Proceedings from an international conference at Björkö, Sweden, 13–17 September 2000. Swedish Society for Nature Conservation/SNF & Ctta. 45 Tryckeri AB. Stockholm.

3.  Hollamby, S., J. Afema-Azikuru, S. Waigo, K. Cameron, A.R. Gandolf, A. Norris and J.G. Sikarskie. 2006. Suggested guidelines for use of avian species as biomonitors. Environ. Monit. Assess. 118:13–20.

4.  International Joint Commission: 1985. Report of the Aquatic Ecosystem Objectives Committee to the Great Lakes Scientific Advisory Board, International Joint Commission, Windsor, Ontario, Canada.