The Conservation of Energy

One of the highest rules in the animal kingdom is the rule of the conservation of energy.  This is also true in the human realm, but is artificially modified by another rule: the division of labor.  If each of us had to go out and forage for our next meal, we would quickly learn about the importance of the conservation of energy.

One of the main things I have seen on the river, which seems to violate this principal, is the osprey hovering.  Hovering takes, what appears to be, an inordinate amount of energy to perform, often with little in the way of return.  Hovering (in energy expenditure) appears to be the equivalent of doing sit-ups or, at the very least, pull-ups.  I watched an osprey recently and noted that it hovered over one area for the better part of an hour.  Now, they don't hover constantly.  They will hover a little bit, soar in a circle, return to the same general spot and hover once more.  They do this over and over again.

What they are doing is trying to spot a fish in a location where they have had a high degree of past success.  The fish aren't always there, though.  So, while they CAN hover, it isn't easy to do.  There are basically two positions to the manuever, both shown here.  The head acts as the fulcrum, which allows their eyes to remain more or less stationary, while their body rocks from an open-winged to a close-winged position.  The legs are extended and allowed to swing to give them balance.  If a fish is spotted, they immediately go into a dive, quickly descending to a position just above the water, where they can hopefully glide in and catch the fish.  From my own experience of watching osprey hover, however, I would have to say that the percentages of success are low.  And that is why I question the method.