What birds build a nest about the size of a queen-sized bed, so large it can be visible from a great distance? And what birds return to the same nest year after year, adding new outer and inner material to their ever-growing real estate?

If you answered "bald eagles" to both questions, then you know quite a bit about this large raptor, and maybe you've even noticed one of their massive nests in the metro area. (See sidebar about metro eagle count.)

The average bald eagle nest runs 4 to 5 feet in diameter and 2 to 4 feet deep. Both members of the pair build and maintain it, soaring in with sticks clutched in their large talons, then grasses and other vegetation to line the interior. As these nests grow year after year, some become so heavy that they topple their tree.

Early on, eggs and then young chicks use a very small part of the nest, occupying a depression in the center called a nest cup, lined with soft moss and eagle feathers. As the young birds grow, they spread out to more of the nest space.

Eagle egg-laying generally occurs between late February and early March in our area. And because the weather then is still wintry, an adult needs to sit on the eggs around the clock to keep them warm. Both birds share these duties, although the female spends much more time incubating than her partner does.

Young eagles grow quickly on their high-protein diet — primarily fish, torn into small bites by a parent — and most leave the nest at about 4 months of age. They still have a lot to learn about living in the wild and feeding themselves, however.

"Just because they're big doesn't mean survival is easy," says Scott Mehus, education director for the National Eagle Center in Wabasha, Minn. He notes that between 50 and 60% of young eagles don't survive their first year, most succumbing to starvation. Other causes include collisions with vehicles and power lines, lead poisoning and fights with other eagles over food.

The big raptors build their nests along metro rivers, in parks and even in a few backyards, with sightings becoming almost commonplace. While eagles in the metro are becoming somewhat accustomed to having humans around, too much activity could lead them to abandon their nest. (See sidebar for tips on not spooking eagles.)

Phyllis Terchanik was granted access to a bald eagle nest on private property not far from her home and captured these photos. She visits every few days, sometimes carrying all her equipment up a steep hill. On other days she observes the nest from a logging road, which gives eye-level views of the nest. She always stays far enough away that the eagles don't seem bothered by her presence.

St. Paul resident Val Cunningham, who volunteers with the St. Paul Audubon Society and writes about nature for a number of newspapers and magazines, can be reached at valwrites@comcast.net.

Eagle etiquette near a nest

Stay at least 100 yards away from the nest tree.
Remain quiet — no shouting, clapping or making other noise.
Move slowly and remain still when near the nest tree.
Don't use flash, if taking photos.
Do not fly a drone anywhere near a nest.

Counting eagles
John Moriarty helicoptered along the metro section of the Mississippi River in early April, counting bald eagle nests on either side of the river. This count, conducted for the National Park Service, ended with a tally of 43 occupied nests.

That is six fewer than last year's count, but as the senior manager of wildlife for Three Rivers Park District notes, eagles regularly change from nest to nest, year to year. They are increasingly moving into metro areas away from the river, thus affecting the count.

Live, on camera
Catch live views of eagles nesting in the metro area on the Minnesota Department of Natural Resources' webcam: www.dnr.state.mn.us/features/webcams/eaglecam/index.html.