Bald Eagle An indicator of wildlife sustainability in British Columbia

What is Happening?

The number of Bald Eagles (Haliaeetus leucocephalus) breeding and wintering in British Columbia has increased substantially since the 1960s. There are now over ten times as many wintering Bald Eagles in coastal BC than during the 1960s (increasing annually by 7.98%) while the breeding Bald Eagle population of BC has increased by an average annual rate of 6.02% over the same period. This is illustrated by winter Christmas Bird Counts (CBC) and the spring Breeding Bird Surveys (BBS) data from Environment Canada's Canadian Wildlife Service long term monitoring sites. These sites represent a sample of the total population, and mirror the overall trend of increasing Bald Eagle numbers.

Source: The Breeding Bird Survey (BBS) annual index data is from B. Collins, 1999. Environment Canada, Canadian Wildlife Service, Ottawa, Ontario. The annual index is the estimated average number of bald eagles that would be seen per BBS route per year if all routes in the area of analysis were surveyed in any one year. Standard BBS analyses require a minimum of 15 routes and in this case 32 routes were available. The trend is the average annual percent change between 1969 and 1998. The wintering data is from the National Audubon Society Christmas Bird Count (CBC) and access through the joint National Audubon Society and Cornell Laboratory of Ornithology web site. Wintering numbers are from up to 10 Christmas Bird Count sites in the coastal region of BC and are expressed as numbers of eagles per site. Winter data is plotted as the previous year as they measure production from the previous year. For example, the 1997 data refers to counts conducted in the 1997-98 winter.

GRAPH DATA

The Pacific Northwest as a region has the highest relative breeding abundance of Bald Eagles in North America and British Columbia has the highest relative winter abundance. A 1994 inventory estimated that 15,000 eagles (9,000 on the coast and 6,000 in the interior) breed in BC and 30,000 winter, mostly in the Georgia Basin (Blood and Anweiler, 1994). During the winter in the Georgia Basin, it is not uncommon to view Bald Eagles congregating along salmon streams in groups of a few to over 3,000 birds.

The rate of increase in the breeding population in BC is slightly above the Canadian average, but below the American average. The rate of increase of the wintering population is well above the North American rate (which is remaining stable), suggesting that eagles from other regions winter in BC. The Bald Eagles wintering along coastal BC migrate to this region from throughout western North America (Yukon to Colorado).

Why is it Happening?

Historically, Bald Eagle populations in western North America have relied on spawned salmon for survival through the winter. However, mining, overfishing and dams have destroyed many salmon stocks. In the Columbia River Basin, mainly due to hydroelectric projects, 99% of stocks are threatened (Nehlsen et al. 1991). Alaskan and British Columbian streams, such as those in the Fraser River Basin, have suffered less drastic declines. The large increase in wintering eagles in coastal British Columbia may reflect the re-distribution of eagle food sources throughout western North America in recent years (Blood and Anweiler 1994).

At present, Bald Eagles nesting in the Georgia Basin produce more young eagles than eagles breeding in other areas of the Pacific coast. Bald Eagles are attracted to urban centres, and landfills, where there is easy scavenging. With the decline in salmon stocks, eagles may have switched to other food sources, such as gulls and waterfowl, that are increasingly more abundant.

Reproductive success of Bald Eagles nesting along
coastal British Columbia, 1990-96

Where seasonal prey abundance and weather conditions fluctuate dramatically, such as Clayoquot Sound, Barkley Sound and Johnstone Strait, eagle productivity is much lower, producing fewer young than needed to replace the adult population. Some of the surplus Georgia Basin immature eagles may disperse to other coastal locations, keeping those populations stable or increasing.

Many factors including prey abundance, weather conditions, toxic contaminants and pesticide poisonings can impact the survival and reproductive success of Bald Eagles in coastal BC.

The regional increase in Bald Eagles reflects a North America-wide recovery of this species after many years of significant decline. During the 19th Century, settlers shot and trapped Bald Eagles and destroyed their habitat. However, the endangerment of the American National Symbol led Americans to legislate the Bald Eagle Act in 1940. Similarly, Canada implemented various federal and provincial protective measures including the Canadian Wildlife Act. But, despite new protective legislation, habitat conservation and public education, Bald Eagle populations continued to decline. DDT (dichlorodiphenyltrichloroethane), an agricultural pesticide first used in the early 1950's, caused widespread reproductive failure among predatory birds including eagles. High concentrations of DDT and its breakdown products (dichlorodiphenyldichloroethylene, DDE and dichlorodiphenyldichloroethane, DDD) are toxic to embryos and can disrupt calcium absorption thereby impairing egg-shell quality. When DDT was banned in 1970, reproductive success of eagles slowly started to return to normal levels. However, DDT remains in the environment for a long time and 31% of Bald Eagle eggs sampled recently (1990 - 1992) from the Lower Fraser Valley still had levels at which production of young can be impaired (Elliott et al. 1996a).

Other types of organochlorine chemicals, PCBs (polychlorinated biphenyls), dioxins (polychlorinated dibenzo-p-dioxins, PCDDs) and furans (polychlorinated dibenzofurans, PCDFs) are also found in coastal B.C. eagle eggs. PCB levels are highest in eagle eggs from the Georgia Basin since these chemicals are associated with industrial sources. Dioxins and furans result mainly from bleaching processes at kraft pulp mills, and concentrations in eagle eggs collected near pulp mills are five times higher than eggs collected from less industrialized areas of coastal BC (Elliott et al. 1996b). In 1990, organochlorine chemicals present in Bald Eagle eggs were double the threshold at which negative developmental effects are noticeable, but have since dropped (Elliott et al. 1996b). This decline is the result of 1977 legislation banning the use of PCBs in Canada and regulations to pulp mill processes implemented in 1989 which reduced the production of dioxins and furans. For more information on the presence of these compounds in BC, visit the regional indicators on dioxin/furan levels, toxins in Great Blue Heron eggs and PCBs in cormorant eggs.

During the 1980s, yet another threat to Bald Eagle survival surfaced in the form of lead shot. The scavenging habits of Bald Eagles, which include the selection of impaired (and often contaminated) prey, can result in their exposure to toxic chemicals such as a lead. Bald Eagles can accumulate large amounts of lead by feeding on waterfowl that have lead shot imbedded in their tissues from non-lethal gunshots or by foraging on waterfowl which have ingested lead shot while feeding. An estimated 2.4 million waterfowl died each year from lead poisoning in the USA, prior to a 1991 US-wide lead shot ban (USFWS 1986). Between 1988 and 1991 lead shot caused 10% to 15% of post-fledgling Bald Eagle mortality (Elliott et al. 1992). Since the 1991 partial BC ban on lead shot, this number has dropped to about 5% (L. Wilson, CWS, per. comm., August 1999).

Why is it Significant?

The recovery of Bald Eagles is ecologically significant since they are keystone predators that help regulate other bird populations. In particular, juvenile eagles raid cormorant and gull breeding colonies by scaring adults off their nests, and either taking young directly or allowing crows and gulls (in the case of cormorants) to feed on chicks and eggs. Bald Eagles may also impact Great Blue Heron populations in BC, by preying on juvenile herons still in the nest.

Bald Eagles benefit BC's ecotourism industry. For example, a 1998-99 survey of the annual Brackendale winter Bald Eagle Festival, conducted under the auspices of the Squamish Estuary Conservation Society, found that 4400 visitors came to the area primarily to see eagles, resulting in an estimated economic benefit of $85,534 to the Squamish community (Eagle Watch Interpreter Program, Visitor Survey, January 1999). Other Bald Eagle festivals include the Goldstream Eagle Extravaganza, near Victoria, and the Harrison-Chehalis Eagle Festival in the Fraser Valley.

What is Being Done?

Environment Canada's Canadian Wildlife Service continues to monitor Bald Eagles for toxic contaminants including chlorinated hydrocarbons, lead and pesticides as well as for new chemicals. Environment Canada, Agriculture and Agri-Food Canada (AAFC) and the federal Pest Management Regulatory Agency (PMRA) work together to remove chemicals from local markets found to negatively impact Bald Eagles and implement changes to legislation which reduces releases of these chemicals to the environment.

Other causes of eagle mortality, such as electrocution, are also being addressed. BC Hydro is trying to reduce the incidence of electrocutions by experimenting with various types of structural changes to utility poles and lines. A national ban on the use of lead shot for hunting most migratory birds became effective September 1999.

A number of organizations including the Canadian Wildlife Service, BC Ministry of Environment, Lands and Parks and the forestry companies of Scott Paper Ltd. and MacMillan Bloedel Ltd. have conducted regular surveys of Bald Eagle nest sites for the past 10 years. The purpose of the surveys is to inventory nest sites and identify particularly important breeding areas for habitat protection. Provincial regulations prohibit the removal of eagle nest trees and suggest a 150m buffer around them. However, the 150m buffer guideline does not apply on private land, and loss of old-growth Douglas-fir forests (common nesting trees for Bald Eagles) may impact eagle populations. The provincial government has also protected critical Bald Eagle wintering habitat by designating as a Wildlife Management Area that portion of the Squamish River where eagles routinely congregate.

For more information contact: John.Elliott@ec.gc.ca or Laurie.Wilson@ec.gc.ca

Check the following sites for additional information on this indicator:

• Hinterland's Who's Who
• Bald Eagles returning to Lake Erie
• Canadian Bird Trends Database for Bald Eagle
• What you can do for wildlife
• Lead poisoning of water birds

The following Web sites are not under the control of Environment Canada (EC) and they are provided solely for the convenience of users. Environment Canada is not responsible for the accuracy, currency or the reliability of the content. Environment Canada does not offer any guarantee in that regard and is not responsible for the information found through these links, nor does it endorse the sites and their content. Users should be aware that information offered by non Government of Canada sites that are not subject to the Official Languages Act, and to which Environment Canada links, may be available only in the language(s) used by the sites in question.

• Bald Eagle winter (CBC) and breeding (BBS) distribution
• US Fish & Wildlife Service - The Bald Eagle is Back

For references used in this indicator click here