Another Bald Eagle Adopts Red-Tail Hawk
Biographical note:
David Hancock, eagle biologist, & Director of the Hancock Wildlife Foundation.
In my 69 years of following bald eagles I have studied how this adaptable fish eagle and scavenger has, once not persecuted by humans, adapted from wilderness living to living very successfully in cities and among humans. HWF introduced popular Live Streaming EAGLE Wildlife CAMS to the public. We specialize in building eagles’ homes where their food supply exists but the nesting options have been long removed by humans. www.hancockwildlife.org
A fascinating biological dilemma: To feed or to eat?
When is live prey brought to a nest to be eaten or be fed a dinner? This decision is faced by most predators, particularly those raptors who will scavenge or predate nestling chicks. This dilemma is really apparent when the predator’s own eggs hatch and there below them is a little helpless chick, looking not at all different from some other chick they had predated yesterday and had eaten for dinner. What stops a bald eagle eating its own chick vs feeding this struggling little creature it just hatched?
Of course ‘maternal instincts’ readily come to mind as an answer. But what is the trigger mechanism? The challenge for many predators just hatching their eggs is making this distinction every time, correctly! Eating a gull chick, a baby crow or a nest full of newly hatched red-tail hawk chicks is commonplace. As a raptor biologist I have seen these examples repeated many times. I have even seen the eagles kill larger red-tail hawk chicks that were too heavy to carry and were eaten in the hawk nest. I have closely followed four bald eagle – hawk adoptions where this normal predator prey relationship has become a parental adoption, like in the recent San Jose, California case now being discussed. Is ‘parenting the prey’ a biological safeguard or an example of nature screwing up? This San Jose eagle photo captured by Doug Gillard carrying the live red-tail chick from the red-tail nest to the eagle nest is the first time we have been able to see this story so completely documented.
Once again the eagles seem to have responded by feeding the newly arrived prey item, the red-tail chicks, rather than tearing them up and eating them or feeding them to their eaglets. But why? There are several theories, but I favor the one that suggests the prey red-tail chick, if alive, and released into the nest, and as it is approached by the adult eagle, the chick opens its mouth and gives a begging call. The red-tail chick may now be hungry and this big Mama approaching perhaps can provide food! Perhaps the “in the nest instinct of the eagle parent is to first give precedent to feeding large-beaked chicks making appropriate begging calls” is the operative hypothesis. So the lucky red-tail is fed – not torn up and eaten.
Is this too simple an explanation? Perhaps not. It is usually the simplest explanation that is right – most of the time! Remember Occam's razor: the problem-solving principle that recommends searching for explanations constructed with the smallest possible set of elements! This seems so logically acceptable to me. This ‘in the nest selective behaviour hypothesis” seems to also apply to why the adult eagles, or other predators, respond by not eating their own newly hatched chicks.
That this hypothesis involves the trigger of the parent recognizing the combination of possibly both a big beak and more importantly a recognized begging call is kind of insurance against wasting a good meal vs killing off your own offspring and species. A young gull, duck, cormorant etc., to their loss, do not have the large hooked beak and gape of a young eagle. Most importantly, they don’t have a begging call resembling that of an eagle. They are food, not young to be fed. This hypothesis supports the eagles, or other raptors, feeding their own newly hatched chicks as well as adopting these closely related species like red-tail hawk chicks. This is a simple, better to be safe than sorry approach! Of course as we have seen in several cases, some of the arriving red-tail chicks are either already dead or wounded and die shortly after arrival. They are then simply eaten – as are young eaglets that die in the eagle’s nest. They did not beg for food!
This San Jose example offers another interesting question -- but one needing more definitive behavioral observations than I have yet seen. Jann Nichols, a Redding photographer has been regularly travelling to record this nest’s activities in wonderful detail. She is suggesting that some of the interchange between the red-tail hawklet and the eaglet is suggesting that the eaglet might be assisting the hawklet by feeding it. I am not sure from watching the few shots I have seen that this is an intentional act or the hawklet quickly taking advantage of the eaglet being near and snatching food from its bill. This is commonly observed by sibling eaglets or hawklets. They regularly steal from each other. But, her suggestion of the eaglet ’perhaps’ intentionally feeding its smaller hawklet nest mate is another big jump in my estimation. Perhaps, as she is inferring, the eaglet is drawing upon normal yet hidden maternal instincts -- a bit prematurely released!
Thanks to two very observant and caring photographers, and the guidance offered by Terri Lhuillier who found and oversaw the earlier Redding bald eagle red-tail hawk adoption a few years back, this fascinating wild interaction of two highly successful species is revealing more answers – and even more better informed questions.