[Tweeters] Bald Eagle peep show....(long)

Martin Muller martinmuller at msn.com
Tue Mar 8 22:13:09 PST 2016


Tweeters,

I’m keeping an eye on a few of our local Seattle Bald Eagle nests, to see when incubation starts (just to confirm that Bud Anderson’s find of an incubating eagle almost two weeks ago was indeed an early date, and to see if the early date is an anomaly or more wide-spread).

I found myself with some “spare” time this afternoon so I stopped off at one of our bluff nests. I got my answer relatively quickly. An adult male and an adult female perched on a branch above (what I assume is) their nest. As I walked up they were in the midst of a hissy-fit, throwing their heads and calling loudly, as an immature flew by overhead.

In order to make sure I didn’t show up during a break in incubation or a change-over in incubation duties (the longest time I’ve seen both adults off eggs once incubation starts is about 30 minutes), I made myself comfortable and did what I like best about bird watching…. show up, stick around, and see what happens. As is almost always the case, I was richly rewarded.

First one immature bird landed in the top of the nest tree. The adults watched intently, but made no attempt to chase the visitor off. Who knows if this is one of their young from last year (a common question people pose when an immature shows up near a nest)? No way of telling without any markers on the bird.

I did not see any signs of molt so this youngster, although officially aged as a second year bird (after January first), was decked out in all the feathers it had grown while in the nest (last year), wherever that may have been. One “easy” way to spot this is when you see the trailing edge of the wings and all the secondaries are exactly the same length. If the bird had gone through a (partial) molt, some of those secondaries would be shorter and the trailing edge starts having a ragged appearance. As the bird landed, wings spread wide open, the trailing edge was completely smooth. The youngster looked at least as big as the adult female, which explained why the male made no move to chase her off. However, the adult female didn’t chase her off either, which surprised me. I guess that’s what immature plumage will do for you: identify you as no serious competition….

As I pondered this, the adults did another bout of head-throwing and calling. The whole neighborhood echoed with their shrill announcement of their presence and hegemony over their territory, even while "entertaining company." It attracted several people walking by, and…another large (female?) immature bird who came sailing by, circled, and then…joined the party and landed next to the first immature, in the top of the nest tree. I have, in many hundreds of hours of observing Bald Eagles, never seen this. Usually, the adults call, and the youngster keeps on going. Upon close scrutiny of this latest arrival, I concluded this bird was at least a third year bird (several “generations” of feathers on the wings).

My puzzling over its plumage was interrupted by yet another screeching salvo by the adults and a third (large) immature sailed in from along the bluff and landed a bit lower in the nest tree. Holy smokes!

As I was contemplating the spectacle of five Bald Eagles in the same tree in Seattle…in March, the adults got themselves all riled up again, but this time with a twist. The smaller male jumped down onto the branch next to the female, she invited (leaned forward slightly with partially drooping wings), the male mounted and they copulated. Normally copulation takes about 7 seconds or so (yes, I’ve seen so many I’ve actually timed them…). This one, watched intently by the three youngsters, took well over 15 seconds. Significantly longer than normal. Makes one (me at least) wonder. Simple act of trying to fertilize eggs, or was there another message being sent? But maybe I’m overthinking / anthropomorphizing this.

The male dismounted but stayed right next to his mate on the same branch. For about 20 minutes nothing happened. Then the adults vocalized again, and within two minutes two more immature (both third year I think) eagles flew by, scrutinized by ten eagle eyes and a dozen human eyes (and a few cameras).

By now it was clear to me that incubation had not started here yet. Well over an hour lapsed and neither adult made any attempt to go to the nest. Ten minutes later the two top-most immature eagles took off, frolicking along the bluff, diving after one another, rolling over and presenting talons, but in a rather lazy and relaxed fashion, without any urgency or drive, leading me to interpret this as play, rather than aggression. Shortly thereafter the adult female took off, the male hot on her heels, and they disappeared around the bluff in the opposite direction from the youngsters. One lone immature remained in the top of the nest tree.

It appeared the adults had not gone far. A few minutes later they could be heard calling (attracting additional human observers). Within a minute an immature flew in from the direction where the adults had been heard, and landed in a tree along the bluff near the nest tree. Another third year bird, with exquisite “golden-tipped” crown feathers, (function of the hazy low afternoon sun) and several upper wing coverts with their white bases showing.

I always try to make sense of my observations (doesn’t always work). I would expect, with so many Bald Eagles around, that the male would perform mate-guarding, to ensure paternity. Hence his sticking close to the female. I was still puzzled by the lack of aggression towards the intruding youngsters by the female. With egg laying imminent, perhaps the female is going through egg-lethargy (something we’re quite familiar with in female Peregrine Falcons just before laying eggs), where she spends more time sitting and, one suspects, takes no unnecessary risks that could jeopardize the developing eggs inside her body. Like chasing off immature females who don’t really pose a serious threat to her postion as the territory-owner. Maybe that explains why she “tolerated” the three youngsters in “her” nest tree. I’ve seen incubating eagles get up off their nest to drive youngsters (of the same sex) out of their territory. Upon spotting another female “violating" her air space, she would call, and if the bird didn’t leave fast enough, she would leave the nest and chase her. The male, in the mean time, would take over incubation duties. Intruding males would be chased off by the male territory owner. Perhaps the lack of aggressiveness (chasing) by the adult female emboldened the youngsters to the point where they landed in the nest tree. If the female’s lack of aggression is indeed the result of her urge to protect developing eggs, I expect her to be chasing youngsters again after she lays the eggs.

More observations needed…..
Oh, goody!

Martin Muller, Seattle
martinmuller at msn.com




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