Spring is a time for nest building; whether it’s a new nest made from twigs or a hollow spot in a rock needing only a fresh supply of moss for padding, birds know they must prepare their homes for the eggs and chicks that will soon follow.
Our weather is slowly warming here on Kodiak Island. Most days we creep into the forties, but then we drop back into the low thirties at night. I see a few sprouts popping through the ground, but mostly, it still looks like winter here.
Animals are the one, true indication spring is right around the corner. I hear whales exhaling in the pass near our lodge, signaling they are following the krill and small fish into the bay. In turn, the krill and fish are here to feed on the phytoplankton which blooms as the water warms. Yesterday, kittiwakes arrived in a big swarm to repopulate the rookery in front of our lodge. Puffins and arctic terns should be here soon.
The surest promise of spring, though, is the circling eagles high in the sky as they perform their mating ballet. Soon, they will begin repairing their homes as they prepare for their young to be born.
Bald eagles build the largest nest of any North American bird. The nest may be as large as 8 ft. (2.44 m) across and weigh one ton (907 kg). An eagle pair often uses and adds to the same nest every year, causing the nest to grow over time.
Bald eagles build their nests in large trees near the water. In Alaska, nests are usually found along saltwater shorelines or rivers, and in many parts of Alaska, eagles nest in old-growth timber. On Kodiak Island, eagles prefer to nest in black cottonwood trees, but in areas where black cottonwoods are not available, nests can be found on rocky cliffs or at the bases of alder trees on cliffs along the coast.
The nest is usually built in the crotch of the last set of branches one-third to one-quarter of the way down from the top of the tree. Eagles tend to nest in trees with sparse foliage near the edge of a habitat, so they can fly to and from the nest without having to navigate through a canopy of trees.
The nests are built of sticks, and each year the eagle pair adds new branches and other vegetation to the nest to cover over food remains, feathers, and other debris left from the previous year. Branches and twigs are placed on the edge of the nest, while softer vegetation such as leaves, grass, and moss are placed in the center. An eagle pair continues to add branches, moss, and grass to the nest all summer until the chicks are nearly grown. Researchers believe the reason for this may simply be to keep the nest cleaner. Waste, rotting fish, and even the bodies of chicks that have died in the nest are not tossed out of the nest but are buried by moss, grass, and other greenery. It is important to keep the nest clean, so parasites don’t infest the chicks.
An eagle pair usually uses a nest until either the eagles die or something happens to the nest or the tree holding the nest. Mates may build two, three, or even four nests in their breeding territory, and scientists are unsure what the purpose is for these multiple nests.
The average distance between occupied nests is usually 1 to 2 miles (1.6 – 3.2 km), but nest sites are often closer to each other in areas where food is plentiful. A 2007 nesting and productivity study on the Kodiak National Wildlife Refuge identified 1141 nests with 439 (38%) of those nests active. This was down from a 55% occupancy rate found in a 2002 study. Of the 439 active nests in 2007, 208 of the nests (48%) were successful in producing young. The researchers suspected the harsh spring weather in 2006 and 2007 might have contributed to the reduction of nesting effort.
Nesting and breeding bald eagles are territorial and defend their nests from other animals, including other eagles. Adults spend much of the day perched in prominent trees near the nest, perhaps to make themselves more visible to intruders. A resident eagle will warn an approaching eagle with a loud call consisting of grunts followed by a high-pitched screech. Sometimes the resident eagle quietly escorts an intruder out of the area, but occasionally, one of the two birds will attack the other, resulting in a display known as cart-wheeling, where one eagle descends on the other eagle, and the other bird rolls onto its back while both eagles grasp talons. The two birds then tumble toward the ground, separating just before they crash.
I welcome the birds back after a long winter. They are often noisy neighbors, but their cries herald birth, life, and spring!
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Robin Barefield is the author of three Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter. To download a free copy of one of her novels, watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska.