The largest “top of the food chain” bird inhabiting the Door Islands is the bald eagle. The scientific name, Haliaeetus leucocephalus, signifies a sea (halo) eagle (aeetos) with a white (leukos) head. This species can grow to more than 33 inches long with a wing span of up to eight feet. Females are larger than the males.
Bald is an old word for white-headed, therefore the name.
Bald eagles take roughly five years to mature sexually. During that time they acquire the white head and tail and lose the patchy pattern of the immature plumage.
Bald eagles can live more than 30 years. Their preferred diet is fish, but they also take water birds and other opportune prey.
These gracious raptors were on the endangered list for more than twenty years. During that time, very efficient pesticides, such as DDT and PCBs, came into common use. These long-lived chemicals ended up in natural environments worldwide and concentrated in eagles, ospreys and other fish-eating birds as well as falcons.
The physiological effect was the thinning and breakage of eggshells, therefore causing breeding failure, and contributed ultimately to the banning of these chemicals world-wide.
During 1990s, bald eagles were able again to lay normal eggs and hatch them, often with two to three eaglets surviving. The population started to rebound.
Bald eagles are still protected by the Bald and Golden Eagle Act to insure their continuing success.
If the adults and nests are disturbed during the period of nest building and courtship, followed by the egg laying and the young hatchling periods, then nests are prone to desertion. During the next four to eight weeks, the young in the nest are moderately vulnerable (banding time).
As the young begin to fledge, they again are highly vulnerable to accidental flushing and likely death. The total vulnerable period in our region runs from December or January to early July.
Regular uses of a road for example, that precede the building of a nest in a bald eagle territory, may not be a disturbance. A specific visit or new activity at a very vulnerable time is likely to be problematic.
Monitoring of the state’s bald eagles in our area is currently conducted by Wisconsin Department of Natural Resources and other agency personnel and assisting citizens.
The first flight in April determines whether eagles have repaired their nests and laid eggs; the second in mid-May is to assess their hatching success and to band the young.
In recent years, as many as 10 new territories have been discovered in this area of the state. Many of the nests on the islands were originally built by inland eagles. These birds were not banded and no information is available about them.
The current state of eagles on the Door islands is assessed as follows: On Rock Island, an inactive eagle’s nest was first discovered in 1997, not successful in 1998, and fell apart in 1999. In 2002, a new nest was started and has produced two young every year.
On Detroit Island, a bald eagle nest was documented in 1999 with two young hatched. It was thought that this pair moved to Plum Island in 2002.
A new nest was built on Detroit in 2002 and was remembered as being successful with two eaglets each in 2006 and 2011.
Plum Island’s nest contained three young in 2002. In subsequent years, this nest’s productivity was two to three young per year dipping to one young from 2007 to 2011, with no activity in 2012.
Susie’s Island had a nest started about 2004 which was active in 2008, with the adult eagles on a constant watch above the area; that nest fell apart in 2009.
In 2012, four active territories were located on Washington Island with two nests holding three and two hatchlings. Additional nests have been discovered. We will update this story at a later date.
A ride on a Washington Island Ferry is sure proof that bald eagles have returned to the islands. At least two adults can be seen keeping a watch from the top of the posts near the old fog signal building on the southwest side of Plum.
Additional eagles may be seen feeding along the Washington, Detroit and Plum shores and on the reefs near the Plum Island boathouse. Even in winter, Island folks have observed up to 14 eagles in the area.
You can adopt an eagle’s nest. Visit dnr.wi.gov/topic/endangeredresources/adopt.
Thank you to Ken Stromberg, USFWS; Ken Easterly and Randy Holm, WDNR; Dick Purinton, Connie Essig, Melody Walsh, and others from past conversations.
By Sandy Ursula Petersen
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