The American Bald Eagle: An Endangered Species Success Story
In June 2007, the United States Fish and Wildlife Service (USFWS) announced that the bald eagle was being removed from the endangered species list, a proposal in the works since 1999.
| Raptor Species American Kestrel Burrowing Owl Cooper's Hawk Marsh Hawk Osprey Red-tailed Hawk Snowy Owl |
The history of the American Bald Eagle and its listing and delisting process reads like a text book case in endangered species creep. Wildlife species of all categories, animals, birds, plants, rarely ever suddenly disappear. Their population declines and eventual extinction are better categorized as a slow and steady process, spurred on by habitat encroachment and, more often than not, technological changes.
Declines in bald eagle populations neatly fit this general pattern. Following the end of World War II, residential and argricultural development projects in the United States began exapnding into bald eagle habitat. With it came the use of the pesticide, dichloro-diphenyl-trichloroethane (DDT).
As DDT spread down the food and water chain, to animal, plant and fish life, mature female eagles ingesting any of these materials also ingested the DDT. DDT bioaccumulation in the eagle's fatty tissue blocked the female's ability to produce calcium, causing the egg shell walls to thin, making them vulnerable during incubation.
Eagle populations fell dramatically.
| Table 1 Bald Eagle Pairs - Year/#pairs 1963 - 417 pairs 1974 - 791 pairs 1984 - 1795 pairs 1994 - 4449 pairs 1998 - 5948 pairs 2006 - 9789 pairs Source: USFWS Region 3. |
Once removed, eagle populations slowly began improving. Table 1 shows the thirty plus year pattern of nesting pair recovery following DDT ban.
Bald Eagle Characteristics:
The bald eagle is a large raptor. The characteristic adult plumage consists of a white head and tail with a dark brown body. Juvenile eagles are completely dark brown and do not fully develop the majestic white head and tail until the fifth or sixth year. Fish are the primary food source but bald eagles will also take a variety of birds, mammals, and turtles (both live and as carrion) when fish are not readily available. Adults average about three feet from head to tail, weigh approximately ten to twelve pounds and have a wingspread that can reach seven feet. Generally, female bald eagles are somewhat larger than the males.
Breeding pairs of bald eagles unite for life or until the death of their mate. The breeding season varies throughout the U.S., but typically begins in the winter for the southern populations and progressively shifts toward spring the further north the populations occur. The typical nest is constructed of large sticks and lined with soft materials such as pine needles and grasses. The nests are very large, measuring up to six feet across and weighing hundreds of pounds. Many nests are believed to be used by the same pair of eagles year after year. Female eagles lay an average of two eggs; however, the clutch size may vary from one to three eggs. The eggs are incubated about 35 days. The young fledge nine to fourteen weeks after hatching and at approximately four months the young eaglets are on their own. (Source: USFWS).
© 1999-2007 Patricia A. Michaels.