Baldy is back. The breeding success of Bald Eagles along Canada’s coasts, rivers, lakes, cypress swamps and other watery habitats has led to a 0.6-percent-per-year increase in eagles over 26 years along 844 migration routes in 44 U.S. states.
By Rex Graham
That’s actually a slower than the 1.9 percent annual increase projected earlier for 1986–2010. “We believe trends reflect post-DDT recovery and subsequent early effects of density-dependent population regulation,” five researchers wrote in the September 2015 issue of Journal of Raptor Research.
Washington state birdwatchers, photographers and eagle enthusiasts are leading the cheers for the recovery. Trogon Tours even offers an eagle photography workshop in June as the clever birds feed on stranded fish at low tide on Hood Canal, Washington, U.S. This is one of the favorite spots of wildlife photographer and workshop leader Nate Chappell to photograph feeding behavior and interactions with herons.
Bald Eagles were completely eliminated from many habitats during the worst of the DDT crisis, including the Channel Islands off Southern California. However, they have been reintroduced there. Researchers with the University of New Mexico, Santa Barbara Museum of Natural History and the Institute for Wildlife Studies found that eagles are doing what they’ve always done on the islands.
“The proportion of seabirds consumed by eagles on the Northern Channel Islands today is similar to that consumed by eagles from this region historically and prehistorically,” the researchers wrote in the August 2015 issue of The Condor.
The highest densities of the raptors with a wingspan up to 8 feet (2.4 m) were scientifically measured in 1970-2009 along the southeast Alaska coastline; Amchitka Island, Alaska; British Columbia, Canada coastline; Besnard Lake, Saskatchewan; Yellowstone National Park; Placentia Bay, Newfoundland; Snake River in Wyoming; and Nemeiben Lake, Saskatchewan, according to a paper in Avian Conservation Ecology.
Finding a 6-foot-wide (1.8-m) eagle nest is surprisingly difficult because they very effectively hide their nests in dense forests.
Pesticides and Bald Eagles
DDT was responsible for thinning the egg shells of many birds that eat fish or other small, exposed animals. The birds most affected were Bald Eagles, Brown Pelicans, Ospreys, Peregrine Falcons and American Robins. DDT was first used to kill mosquito larvae and beetles that carry Dutch Elm Disease.
DDT and other organochlorides have been replaced by organophosphates, which are highly toxic to birds, but break down quickly and don’t accumulate in the food chain like DDT. However, there is evidence that birds exposed to organophosphates in pest-control products behave aberrantly and may be selectively captured by American Kestrels, which could be at risk of secondary poisoning.
Most recently, neonicotinoids and Fipronil are the fastest growing pesticides around the world. A review of 150 studies of the effects of the pesticides on vertebrate wildlife found that the biggest impact may be loss of insects and other prey.
“The systemic insecticides, neonicotinoids and Fipronil, are capable of exerting direct and indirect effects on terrestrial and aquatic vertebrate wildlife, thus warranting further review of their environmental safety,” scientists with the RSPB Centre for Conservation Science, the University of Saskatchewan and Pierre Mineau Consulting wrote in Environmental Science and Pollution Research.