Thursday, February 9, 2017

An ever-growing eagle aerie

Our national avian symbol, the Bald Eagle, sits with apparent pride atop a large aerie that it and its mate have jointly constructed. This nest is already massive, in spite of "only" being five or six years old. Bald Eagles will reuse nests for many years, and add material constantly.

A few weeks back, I spent a frigid, snowy, windy day watching the comings and goings of a pair of eagles in eastern Ohio. The nest is in an easily viewable locale, and attracts scores of onlookers. Fortunately, because of the Arctic weather during my visit, few others stopped by. It can become quite a circus along this road, I am told, but the gawking onlookers don't bother the birds a whit.

I had only planned on staying here for a few hours, but that stretched into 6-7 hours by the end of which I had nearly lost feeling in my extremities. Well worth it, though, to spend time watching the birds add sticks to the nest, interact with each other, and the world around them.

Some flyby American Crows divert the pair's attention briefly. While the sexes look identical, there is a conspicuous size difference. Females are bigger; up to 25% larger than the males.

This nest is in a large, seemingly healthy American beech (Fagus grandifolia). Here, one of the birds goes out on a nearby limb and snaps free one of the beech's branches. Beech are pretty tough, and as long as the tree remains healthy it should provide good supporting superstructure for the massive nest within its boughs.

An eagle prepares for landing with a bundle of sticks. These will be artfully threaded into the nest, and from my observations, usually by the female. Most times, nesting material was collected far from the nest and outside my field of view. On at least one occasion, an eagle flew into the stubble of a nearby corn field, and returned with talons full of old corn debris.

 A stick is carefully jimmied into position, while the other eagle watches attentively.

I'm not sure which sex is which here, but a minor spat had broken out over who would handle the insertion of a branch. It seemed that most times, when the smaller male would return with twigs, the female would soon appear if she wasn't already there, snatch them away and place them herself.

Bald Eagles are the second-largest raptor in North America, weighing up to 14 lbs. Accordingly, the birds can handle big sticks.

A landscape style shot illustrates the size of the aerie. Hard to believe its only about five years in the making. The mother tree has a lot to do with how large the nest can get. The arrangement of large limbs anchoring the nest dictate how tall the birds can pile the sticks over time. As this nest is in the crotch of a couple of very large sturdy trunks, and those trunks remain close together as they ascend, it appears that the birds can continue to expand upwards for quite some ways.

Big eagle nests can be their own downfall. As size and weight increase, the nest becomes more and more of a liability to the anchoring tree. Eventually windstorms can topple the nest, shear off branches to which the nest is attached, or even bring down the entire tree.

Photo credit: Francis Herrick

Here's the gold standard for giant Bald Eagle aeries: the so-called "Great Nest", which was located in Brownhelm Township, Lorain County, Ohio. This nest was about 12 feet from top to bottom, nearly nine feet across at the summit, and eventually attained a weight of around two tons. By the time the tree collapsed during a great storm on March 25, 1925, the nest had been in use for some five decades. It was anchored in a sturdy shellbark hickory (Carya laciniosa), and that probably explains much of the nest's longevity. Professor Francis Herrick of Western Reserve University spent years studying these eagles, even erecting a lofty observation platform in a nearby elm from which he could better observe and photograph the birds.

It'll be interesting to see how large the aerie featured in this blog eventually gets. Only time will tell, but the somewhat protected nature of the site, health and sturdiness of the tree, and the arrangement of the support limbs suggest that the nest will grow much larger than its current size.


Scott said...

Those are some great pictures, I can't believe you sat there for 6 hours. Just curious, was this in the Cuyahoga Valley National Park? I was going to head there soon to see the nesting eagles in the park. Thanks for sharing.

Lisa at Greenbow said...

I giggled about the eagles having a "spat". We have a nest that can be watched from fairly far away. It seems they often voice their opinions about this and that. Amazing how large these nests can become.

Jim McCormac said...

Thanks for the comments, and no Scott, this nest is quite some ways from Cuyahoga Valley NP


As always, click the image to enlarge At the onset of last Monday's aquatic expedition (perhaps more on that later) to Rocky Fork ...