DON'T HAWKS FIGHT BACK?
March 20, 2011
Q: A pair
of red-tailed hawks has nested near our house for years. Several times
I have seen one or both of them harassed by crows. I watched a five-minute
dogfight today with the hawk just trying to get away. It was very entertaining,
but puzzling. Why do these large raptors let the crows that are less than
half their size and without their weapons harass them?
Q: I have
seen crows pester a couple of big hawks. Sometimes the hawks just sit
on a tree branch and let the crows fly around and make a lot of noise.
Sometimes they fly away, with the crows chasing them. Would the hawks
act differently if they had a nest with babies in it?
A: Very good
questions about a commonly observed phenomenon called mobbing, in which
several smaller birds harass a larger predatory bird. Why would a red-tailed
hawk, bald eagle or great horned owl let a bunch of smaller birds, like
crows, pester it? And why would a smaller bird take the risk of attacking
these large predators? The answer, as is usually the case when animal
behavior and ecology are involved, is complex. Some explanations seem
relatively straightforward whereas others are more speculative.
crows' perspective, mobbing behavior may have adaptive significance in
terms of survival in that a large potential predator may be driven from
an area where crows raise their young because the babies might become
prey for some raptors. In a situation in which a predator such as a large
hawk is simply in between meals, either sitting or flying, and has no
special stake in a particular location, mobbing behavior by crows could
be very effective. The hawk would presumably not find the annoyance worth
the effort of staying around and would move on to another area to hunt.
In other words, the crows don't want the predator in the area and the
hawk itself doesn't really care whether it is there or somewhere else.
of an answer to the question of what a pair of these birds of prey would
do when harassed by crows if they had a couple of babies in a nest, I
asked an ornithologist. In fact, I asked 11 ornithologists. Some are top-flight
amateur bird watchers and some are professional scientists who have studied
hawks or eagles. The answers I got were consistent, and surprising.
that if a red-tailed hawk reached out and grabbed a crow with its talons,
that would be the end of the crow. Or as one of the professionals put
it, in scientific terms, "the crow would be toast." But although
large raptors have the necessary weapons, the energy cost of pursuing
or otherwise attempting to catch a crow is normally not worth it. Crows
are agile creatures and would be very difficult to catch in flight. So
a hawk typically ignores the crows or flies away.
from the bird researchers about what hawks or eagles would do if eggs
or babies were in the nest were especially interesting. Statements like
the following were telling. "I have never seen crows approach when
young were present, but birds of prey will fiercely protect their nests."
One commented, "None of our staff has ever seen crows or raccoons
be predators on an eagle nest with eggs or young in it." Another
said, "I don't know for sure, but when there's a nest involved, the
stakes are higher and the raptor would probably fight back. The crows
know this and keep their distance." Or as another put it, "When
baby hawks are in the nest, the area around it becomes a no-fly zone for
of how hawks respond when crows use their mobbing behavior tactics are
frequent. But what a pair of hawks or eagles would do if crows tried their
antics when eggs or babies are in the nest remains unanswered. Ironically,
the fact that such attacks seldom or never occur, may be because crows
already know the answer.
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