This PBS Nature documentary outlines the life cycle and biology of the iconic Bald Eagle. The plot is centered around two breeding pairs in Iowa and Minnesota. Both nests were installed webcams and have attracted millions of viewers from all over the world. The nests are still active and pairs are now preparing for the breeding season.
The nest in Iowa is next to Decorah Fish Management Station. As a top predator highly adapted for fish prey the location provided an ideal setting for documenting their behavior.
Apex predators are important indicator species about health of the ecosystems. They are vulnerable to pollution arising from anthropological activities. Species at the top of the food chain can accumulate persistent toxic substances through a process known as biomagnification. Bald eagles came to the brink of extinction entirely because of human activities. Their story represents a textbook example of human-wildlife conflict. More than 120 thousand eagles were shot by unfounded reasons such as predation on lambs or snatching of little children. The heavy use of pesticides such as DDT also took its toll. In 1960s there were less than 400 breeding pairs left. Rachel Carson’s Silent Spring was the first whistle blowing book. Published in 1962 it has been highly influential for recognition of the biomagnification problem. Even today many bald eagles die because of lead poisoning when they eat carcasses of deer abandoned by hunters.
US declared the species as “endangered” in 1970s and the population is recovering. The documentary highlights this flagship project run by Raptor Resource Project which is producing scientifically valuable information about the population dynamics of a severely bottlenecked top predator. One curious question is the movement patterns of the newborn which has important implications for wildlife management. After the documentary was released, in 2011 and 2012 two juveniles (named D1 and D14) were tracked by fitting satellite transmitters. GPS coordinates from each individual provided spatial movement information and helped estimate gene flow in bald eagles. D1 traveled all the way up north close to the Arctic circle and impressed everyone. D1 continues to transmit GPS signals to the Argos satellite and as of morning of March 1st 2013 it was near Spillville, Iowa. D1 will turn two years old by April 3rd 2013. Other juvenile named D14 was found electrocuted under a utility pole. Electrocution is one of the major causes of mortality today. Bald eagles also get struck by cars when they are attracted to roadkills.