Kleptoparasitism, literally parasitism though theft, the behavior of stealing food from other animals is a well known behavior in Bald Eagles and well documented when the larger eagles range overlaps that of the smaller Osprey.
However, I had never seen the behavior in Bald Eagles first hand, until now. I have witnessed it on many occasions in gulls, almost comedically pursuing pelicans which never seems to work out for the gull. However this instance is quite different; an Osprey lacks a throat pouch to protect it’s food and can’t simply sit on the water and swallow its prey. This is a strictly aerial dance and the looser goes away hungry at best.
The actual pursuit is eerily reminiscent of accounts of World War 1 dog fights. Essentially the two birds entered a series of turns each trying to out turn the other. However, unlike a dogfight, the eagle didn’t need to kill or even directly attack, and risk injury from, the Osprey. The rules were simple:
The Osprey needed to out turn the Eagle forcing it to overshoot. That allows the Osprey to cover some distance before being forced into the turning battle again. Ultimately, if the Osprey is lucky, it makes the eagle fly far enough that continuing the pursuit becomes undesirable and the eagle breaks off.
The eagle’s position is much simpler; make the Osprey continue evading until it’s too tired to continue with the fish. That difference in strategy makes this a battle that heavily favors the hunter. It needn’t concern itself with actually attacking the target and risking injury, only harassing it long enough that it must abandon the food.
The following gallery shows a Bald Eagle pursuing an Osprey for it’s fish. In today’s chase, the eagle came away victorious with the fish, which it caught in mid air as well.