Hanover Bald Eagle Blog # 30
July 1, 2019
In partnership with Pennsylvania Game Commission and Comcast Business .
There can be no doubt that we all breathed a sigh of relief when Stars plopped back into the nest Sunday evening, not only alive and well, but with a prey item in tow! We will never know what occurred on Star’s walkabout (or fly-about), but his/her apparent health and vigor reminds us of the inherent resilience of bald eagles. We can also view the reappearance of Stars as an indicator that the Hanover eaglets are beginning an elaborate learning process in which trial and error play a strong role in teaching them “how to be an eagle.”
Stars is now taking short forays from the nest, beating his/her wings more often, and spending even more time perched on the edge. Stripes appears less restless, but still experimental and curious about his/her surroundings. We are continuing to see Liberty and Freedom drop food off in the nest, a behavior that will likely continue (though hopefully with less chaos than the startling prey delivery event last week). Increased tension in the nest is normal for raptor families, and as the fledglings get older, their “obedience” may waver. They are antsy, and their neurological development is still expanding which results in testing boundaries and growing curiosity about the world outside the nest.
In their book The Bald Eagle, Haunts and Habits of a Wilderness Monarch, Gary Bortolotti and Jon M. Gerrard describe an amusing event during which two eaglets seemed startled and perplexed by a fish delivered to the nest that was still moving. One eaglet crept forward and barely touched the foreign object, which then flipped over, causing both eaglets to jump back startled. This happened several times, ending with the fish finally flapping itself out of the nest and landing on the forest floor below. Both eaglets hopped over to the edge of the nest and peered over, perplexed. These types of learning experiences are fun to watch and serve as a reminder that humans aren’t the only ones with a “toddler” stage.
There are clear advantages to being a curious youth, and most young birds are characterized by being more exploratory than adults. In the Hanover nest, we have seen examples of this when the nestlings stab at sticks with their beaks or feet, viewed by researchers as a precursor to catching prey. We have also witnessed behavioral explorations, most notable in the recent “mantling” behavior. This is when one of the eaglets spreads his/her wings over food, keeping the sibling and even the parent away from the meal. Adult eagles have a full tool kit of foraging strategies, yet each individual uses a combination of instinctual and learned methods. While there are benefits to testing out new methods as youngsters, both Stars and Stripes will reach a point at which the benefit of sticking to what they know will outweigh the energy expenditure of experimenting with new techniques. We can all relate to the payoff of learning from our mistakes, and for a scavenger, those “aha moments” are also important.
Oftentimes bald eagles learn alongside their sibling. While it’s normal for one fledgling to leave the nest before the other, this doesn’t exclude the possibility of shared learning experiences. By watching each other and their parents, they can see what works and what doesn’t. Once both eaglets fully fledge, they will often remain near each other, keeping proximity to the nest for four-six weeks while they continue to be fed by the parents. They will continue to pick up new lessons as they join communal feeding scenarios such as fish die-offs or shared carcasses where other predators and non- related eagles may be present.
Earlier this week there were several moments during which Stripes and Stars were allopreening, meaning they were preening each other. These two nestmates often nip each other gently and stand side by side. The relatively low levels of aggression at this stage are an example of how apparent “family” dynamics arise at those raptor nests with enough resources to go around. After Star’s fall from the nest, seeing them comfortable back in their shared environment has been a welcomed sight. We’re glad to have you back Stars, and while we look forward to your official take off, we are also eager to observe you both gaining more confidence in your eaglet ways!
SOURCES
Gerrard, Jon M. & Bortolotti, Gary R. (1988). The Bald Eagle: Haunts and Habits of a Wilderness Monarch. Smithsonian Institution.
O’Toole. Laura, T. et. al. (1999). Postfledging Behavior of Golden Eagles. The Wilson Bulletin, 111(4), 472-477.
Marchetti, Karen and Price, Trevor. (1989). Differences in the Foraging of Juveniles and Adult Birds: The Importance of Developmental Constraints. Biological Reviews, 64(1).
Thank you Hawk Mountain for this week's blog entry!
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