How do songbirds and small animals know when there's a hawk in the immediate vicinity?

Question

At any given time in our yard, we have at least 20 birds, up to the same number of squirrels, 15 or so chipmunks, and a few rabbits. Our many feeders and birdbaths are mostly under big trees and next to large bushes, although many of the birds and other things feed more out in the open. Needless to say they're very noisy, and it's a gorgeous cacophony!

Sometimes, all of a sudden, it will get eerily quiet out there, and when we look out, almost everyone will have disappeared into the trees or bushes.

Within a few minutes, a hawk comes through. It doesn't stop, but there have been times it will swoop down and grab something vulnerable, usually a chipmunk, or baby bunny, that hasn't taken cover in time.

A little while after the hawk is gone, everybody comes out again and resumes their regular routine.

I'm curious as to how they know the hawk is in the vicinity. Do some of them see it and somehow communicate that to the rest? Do those who see it hide and others follow suit by hiding even if they don't know why? Does it emit a sound that we can't hear? Is it a smell? In the yard, we've only ever seen one hawk at a time, so it doesn't seem like they feel surrounded.

If it was just a few birds or animals it would be easier to understand, but I'm referring to a variety of sizes, species, speech patterns, nesting behaviors and feeding behaviors.

Answer 1

All it takes is one of the birds to notice and give the alarm and then the other birds join in. Even the chipmunks and squirrels will listen to the birds and then pass the message along.

Birds' lives are so filled with danger that they're on alert at all times, just to stay alive. Luckily, they have several tactics to avoid becoming the next meal for a cat or hawk. One, of course, is to fly away, a good choice, but not always possible. Another is to call in a troop of other birds to set up such a clamor that the predator is driven from the neighborhood. But in cases where the threat is too close and too dangerous, birds freeze in hiding while making soft, high-pitched sounds that serve as a warning to other birds.

In our own backyards, the birds likeliest to call out high-danger warnings are robins and chickadees, and many wild creatures recognize such calls. Catbirds, sparrows, finches and nuthatches dash for safety when they hear a robin's barely-audible-to-humans "seet-seet" sound, because they know a bird-eating hawk is hunting nearby. Even chipmunks, red squirrels and woodchucks heed these warnings, running on their short legs for cover.

Bird warning calls work across species

Studies in recent years by many researchers, including Dr. Greene, have shown that animals such as birds, mammals and even fish recognize the alarm signals of other species. Some can even eavesdrop on one another across classes. Red-breasted nuthatches listen to chickadees. Dozens of birds listen to tufted titmice, who act like the forest’s crossing guards. Squirrels and chipmunks eavesdrop on birds, sometimes adding their own thoughts.

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Studying the phenomenon, he documented a “distant early-warning system” among the birds in which the alarm calls were picked up by other birds and passed through the forest at more than 100 miles per hour. Dr. Greene likened it to a bucket brigade at a fire.

When Birds Squawk, Other Species Seem to Listen

Chipmunks make these calls, too, Greene noticed. He was astonished that mammals and birds — biological families as different as mice and magpies — would share this early warning system.

"We've got these complex communication networks," Greene explains, "and it's not just one species yakking to members of its own kind. It's all these different species — and not just birds, but mammals as well. And they're all sharing information."

Squirrels Mimic Bird Alarms To Foil The Enemy

As for how the first bird knows, it seems to work mostly by sight.