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 Bald Eagle Feeding and Hunting Practices
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By: davidh (offline) on Monday, July 26 2010 @ 10:21 PM EDT (Read 1900 times)  
davidh

1) Is there a shift in the timing of food delivery approaching the fledging process?

It is my experience that the adult eagles "generally" quit feeding the nestling a day or two before fledging. The hunger incentive I suspect is important and getting a little less food probably gives incentive to action.

In the wild I never saw adults feed the young in the nest post fledging. Here in the city they frequently do. I suspect the difference is about the availability of 'secure and safe' landing and perching spots. In the wild every tree, log, rock or piece of beach is undisturbed. An adult can sit anywhere to eat. In the city almost every tree or rock is disturbed every 1.6 seconds by a lady pushing a baby carriage, a dog or bicycle with screaming kids. They learn that the "primary safe place" is the nest and are more tempted to return to it for all feeding and even after the young fledge.

In the wild I not only did not see adults feeding fledglings, even away from the nest, but only rarely, after a few days of no eating, did I ever see a fledgling take anything by force from an adult and that was always by tracking down an adult with food on a remote beach and aggressively stealing it. That of course may have been the learning process.

However, the key to me was that these meals aggressively stolen from parents were about to drive the adults away. It was usually within a few hours to a few days that the adults were gone after such an incident. The abandonment process, about 4 - 8 days post-fledging, was then followed by the fledglings then abandoning the territory in another 4 - 6 days after abandonment by the parents. Unlike the peregrines the young eaglets get no training in hunting, beyond what they see from the nest during rearing.

2) Can weather cause a shift in bald eagle hunting patterns & diets?

I think weather induced changes in hunting tactics is pretty standard. These eagles are such opportunists. If the easiest and most available prey becomes less available then they find a 'next best' and so on. Here, another common option to fit into the mix is the opportunistic "road kill" or the "neighborhood incentive program" -- handouts of salmon steaks, chicken thighs etc. dispensed by neighbors liking their eagles. So many people take pleasure in doing and watching this. I was at a site yesterday where the farmer has several 'snap rat traps" set up and he throws the victims on the barn roof where within minutes the eagles have them.


I see this as the equivalent of eagles of old living for 10,000 years beside an Indian village and daily picking up the offal -- the thrown-out salmon, cod or seal carcasses etc.. It certainly has not handicapped the eagles ability over time to fend for themselves. And it then and now cleans up our villages and streets! Did this cooperative element add to the reasons the natives revered and treasured the eagles?

Robbing other predators is also common. I suspect some of the voles we see coming in are contributed by harriers. And in one case, the first pair to breed on one of the very high electrical towers, the pair actually ate two young red-tails, about 2/3 grown, accompanied by considerable protesting from the adult red-tails. That pair them re-nested in the red-tail nest the next year and have now just fledged 2 young this week.

I think our eagles are doing all the right things to effectively co-habitat with humans.

David


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