Right now, bald eagles are busy building and repairing their nests in preparation for the eggs that will soon be laid in the massive structures. It’s an annual tradition that has held on for millennia.
The birds will bring sticks and other material to their nests, which can end up weighing more than a ton. They’ll carefully build a platform high in a tree, often a dead white pine overlooking the river. Then they’ll get ready to bring a new generation into the world.
Eagles mate for lives, and nest-building is part of their annual bonding, which is essential for successfully mating and raising young. Eagles in Wisconsin begin nest-building as early as January and may lay eggs starting in mid-February.
In the 1970s, the reproductive cycle was almost ended, when eagle populations plummeted. The insecticide DDT caused many birds, including eagles, to lay thin-shelled eggs that broke before chicks hatched. Few chicks survived, and the population was nearly wiped out.
Wisconsin banned DDT in 1972 — the first state in the nation to do so. Eagles got more protection from the Endangered Species Act starting in 1978.
The outlook is better today.
The Wisconsin Department of Natural Resources recently announced the results of its 2019 survey of occupied bald eagle nests in the state. Last March and April, DNR officers flew over the state counting nests, and found cause to celebrate.
In the last five decades, bald eagles have made an astounding comeback from near extinction in the state. In 1974, there were only 107 known nests across the entire state. There are now almost 1,700 known nests in Wisconsin — 15 times as many occupied nests in the state as in 1974.
At least 10 percent of the known occupied nests are in the northwest Wisconsin counties that contain the St. Croix, with counties along the river in the top 10 number of eagles nest across the state.
In fact, numbers in northwest Wisconsin saw slight declines in nest numbers last year. But it’s not worrying to researchers, because they think it might mean eagles have returned to the point that there’s not much room left for more of the birds to breed.
A pair of maps the DNR released drives the point home.
“Northwestern Wisconsin, which had the second-highest number of eagle nests in the state (360), is nearing carrying capacity, which could explain the slight decrease in this area,” said Laura Jaskiewicz, the DNR research scientist coordinating the aerial surveys. “Surveyors for west central Wisconsin believe the late harsh winter may have impacted eagle numbers in that area.”
People who spot eagles engaging in nest-building activity, or an eagle nest itself, are asked to report it to Bald Eagle Survey Coordinator Laura Jaskiewicz at email@example.com.
Anyone can “adopt a nest” by donating $100 to the Wisconsin DNR. Donors receive a certificate, calendar, and an aerial photo showing the location of “their” nest. Funds go to support continued protection and restoration.
Wisconsin taxpayers are also encouraged to donate to the Endangered Resources fund when doing their taxes this year.
Funding from this source has been important to the eagle recovery and ongoing monitoring of the population.
- Wisconsin Bald Eagle and Osprey Nest Surveys 2019 (PDF)
- Eagles in Wisconsin – Wisconsin DNR
- Bald Eagle Numbers Soar 27 Percent in Southeastern Wisconsin, Increases Across Majority of State
The statement that DDT cause thinning of shells has been debunked. Here is an article for the Wall Street Journal stated 2006 that debunks that statement.
The Myth that DDT Caused Egg Thinning and Depletion of Eagles
Greg Seitz says
Dean – Thank you for your comment, this is not a theory I’ve heard before. But that WSJ link is opinion, a letter to the editor, and cites no peer-reviewed science to back up its claims. On the other hand, there have been numerous robust, replicated, and peer-reviewed studies showing how DDT does in fact cause egg-shell thinning. As mentioned in this article and elsewhere, other factors also contributed to the decline of eagles, including habitat loss. Greg