Bald Eagle

Bald Eagle

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Eagle Hunting Techniques

"Typically an eagle will perch near some waterfowl concentration. (The more concentrated and restricted by ice, the better.) It will take periodic 'strafing' runs over the waterfowl. I think this is in an attempt to identify the weaker individuals--just as Emily and the MN students said! The others scurry and disperse. I've seen adults do this over a period of an hour or more, over the same flock. Eventually, out one of the birds becomes exhausted from repeated dives, drowns and floats to the surface."

These are not "dive-bombing fast runs, simply methodical fly overs to disperse the flock. I've seen adults do this over a period of an hour or more, over the same flock, eventually tiring out one of the birds from repeated dives, who drowns and floats to the surface. The eagle then patiently but methodically grabbed the bird from the water, dragged it to the edge of the ice and ate it. They will also take a bird who ultimately moves too slowly after they've tired them out. So, the individuals they ultimately prey on, are indeed the weaker ones of the flock; a natural selection process in the works ! Some of the waterfowl concentrations are in fairly small, restricted areas of small rivers or iced-in reservoirs; I think this helps the eagles. We should remember though, that there are many wintering areas where both waterfowl and eagles co-occur, and in these situations, fish win out every time; definitely the preferred prey.

Q. What percent of eagles' food is fish? Waterfowl?

A. This depends on the wintering area, and thus the prey available. In NY, within our largest wintering area in Southeastern NY, fish makes up over 90 % of the eagles' diet. At one of our smaller areas along the Hudson River north of Albany, waterfowl makes up more than 75% of their diet, while on the Hudson south of Albany, it's back to fish.
How deep under water are the fish that eagles typically catch?

Q.How deep can they see the fish? (Would they be visible to the human eye, if we could hover above the water the way they can?)

Q. Does windy/stormy weather ever seem to make fishing impossible? How much affect does the wind have on water, and does wave action affect visibility?

A. I suspect that eagles can see fish much deeper than they actually ever attempt to catch them. They are much more of a surface fish catcher/eater than going after anything very deep (as an osprey will). I think they don't fish anything deeper than one foot, and in most cases probably 6 inches or less. They also frequently take floating dying or dead fish, likely much more than we realize, unless there is an abundance of near-surface fish prey available. They are much more of a surface "snatcher" than a diver like the osprey. I think most of the fish they see, we could easily see from the air as well. Wind on water definitely affects visibility, which does affect fishing, making it more difficult to "see" fish down in the water. This is a particular problem for ospreys (fish-hawks), who sometimes cannot successfully feed at all on high-wind days. Bald eagles, however, use the wind to their advantage. As we all know, and as I just mentioned, eagles are also big-time scavengers; not too proud to take dead or dying items ! So, during windy days, they position themselves on a good perch on the downwind shore, and simply wait for the wind to float a dead fish their way. Pretty smart, eh ?

Q. Any idea how much more food an eagle might need to eat in the winter when it's cold, compared to the summer?

A. I don't know exactly how much more food eagles need in winter (although there have been some energetic studies done to determine some of this), but like you and me, they require more in the winter than in summer, simply to keep their body temperature up. That is why, in winter, eagles are masters at energy conservation. Especially during harsh weather, they use as little energy as possible, perching, nearly motionless, for hours on end. Studies have shown that as much as 90% or more of a typical eagles' day can be spent perching, loafing and roosting; non-movement activities designed to conserve energy. On mild days, this is obviously less of a concern.

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