Eagle nest artifacts (Photo by Don Reimer)
Eagle nest artifacts (Photo by Don Reimer)
Although it’s now mid-February, plenty of winter weather remains until spring. But don’t tell that to the state’s bald eagles. Across the midcoast region, eagles are making preparations for spring nesting. As additional sticks are added each year, eagle nests can become enormous. A record-setting Florida nest was 6.1 meters deep and 2.9 meters wide, with an estimated weight of nearly 3 tons.

Maine eagles typically select a tall “super-canopy” white pine located in the vicinity of water that affords unobstructed views of surrounding terrain and a clear landing approach. The bulky nest is constructed in the top quarter of the tree, often within a crotch of sturdy branches. Sticks collected from the ground or broken from trees form the interwoven outer frame of the nest. By mid-March, adult eagles are incubating their clutches of one to three eggs. Once that first egg is laid, consistent incubation occurs to protect eggs from the elements and the cold. In coming weeks, be watchful for any nest-building eagles transporting 3- to 6-foot-long sticks in their talons.

The inner nest is lined with sod, weeds, grasses, mosses, seaweed, animal hair or feathers. Once I observed an eagle that had uprooted a sizeable clump of marsh grass for use as nest lining material. With the clump of grass trailing behind, the eagle appeared to wear a shimmering hula skirt. Eagles also add sprigs of greenery to the nest rim throughout spring and summer. Some scientists think the fresh green sprigs might serve as natural insect repellent or may help to keep the inner nest clean. Others speculate the greenery provides some basic camouflage or possibly signals to intruding eagles that the nest is well tended and they should stay away. Once established at a favorable site, successful eagle nests can persist for decades.

Years ago I happened upon a collapsed nest that had toppled to the ground following a punishing windstorm. The entire top of the nest tree was cleanly severed, revealing an intriguing dietary history of the eagle family.

Eagle diets vary regionally. For Maine’s coastal populations, birds make up roughly 75 percent of their diet and fish constitutes approximately 25 percent. The reverse holds true for northern and inland eagles where appropriate avian prey is less available, while odds of capturing river and lake fishes are relatively strong. An overriding dietary principle is also in play: like most raptors, eagles are avid opportunists!

Let’s examine my photo. For illustrative purposes, I arranged the prey remains by categorical order. The skulls in upper left corner are small mammals — a hapless muskrat crossing a stream or pond? A snowshoe hare? Our local eagles kill woodchucks too. Did you notice the two baby snapping turtle shells? Both shells were opened by piercing the side of the shells much in the way we use a can opener to extract the contents.

Pictured below the mammals, a series of cormorant skulls. Double-crested cormorants are a reliable and common food source for eagles during spring and summer. Cormorants are especially vulnerable during low tides when they are less able to taxi across water quickly enough to evade the oncoming eagle. Gulls, ducks and egrets are all exploited as summer food sources.

You may have noticed the matted ball of monofilament fishing line in the lower left that was apparently incorporated into the eagle nest lining. A huge rubber fishing lure and hook was included with the monofilament. To the right of the mono, see an oblong-shaped eagle pellet, consisting of indigestible bits of grayish fur.

Several keel-shaped bird breastbones of varying shapes and sizes are shown at lower right. An assortment of other bird skeletal parts, including the specialized pelvic bones (ilium), completes our dietary tour. No fish remains were found among the nest debris, possibly because fish bones disintegrate rather quickly.