Hungry hawks such as sharp-shinned and Cooper's pose a threat to backyard birds

Do some birds eat other birds?

Yes, a number of hawks hunt and eat smaller birds, and the sight of them strikes terror in the hearts of our backyard birds. If you've ever watched a crowd of songbirds feeding at and under your feeders, then watched them all dash off at once, scattering in every direction, it's likely that a bird-eating hawk is on the prowl.

The ones most likely to visit our urban backyards are the sharp-shinned hawk and its larger cousin, the Cooper's hawk. These sleek raptors are built for speed and maneuverability, able to snatch a bird in flight.

In my own backyard, the first sign that a hawk is around but not visible to me is a woodpecker "frozen" to the peanut feeder. Downy woodpeckers, especially, plaster themselves to the feeder when they detect a hawk is around. Immobility is safer for them, with their slow, undulating flight, than trying to outfly a deadly hawk. A look around the yard shows no sign of any other birds, which is unusual.

It can take a long time after the hawk departs before the small birds feel comfortable coming back to the feeders.

Reader Bob Hilbert recently sent a photo and description of a sharp-shinned hawk behaving in a way that I'd never seen before: The hawk flew into his backyard and perched on an arbor for nearly an hour. Hilbert was astonished to see the many birds at his feeders ignoring the hawk as they went about their birdy business.

What was going on? Had the hawk already eaten and was now resting while it digested its latest meal? But if so, how could the small birds know that they were being watched by a hawk that was too full to eat?

"Prey species can learn to recognize and react to subtle clues that reveal if a raptor is either hungry and hunting or not an immediate threat," said Stanley Temple, a noted ornithologist and conservation biologist at the University of Wisconsin-Madison.

Back in the 1950s a researcher tethered a red-tailed hawk to various perches outdoors. Half of the time the hawk was hungry, the rest of the time it was well fed. The songbirds in the area devoted more energy to driving away the hungry hawk than they did when it had just eaten.

The consequences for ignoring a hungry bird of prey can be dire for smaller birds, so they quickly learn to "read" predators. They watch for signals such as whether the hawk's plumage is compressed, whether it's standing on both feet with eyes wide open and seems very alert. There doubtless are other clues too subtle for the human eye.

How do they learn this? Temple said that birds watch each other, with an inexperienced bird copying the way a more experienced bird responds.

The world is a dangerous place for birds and they must be adept at reading their surroundings. They need to eat, especially in cold weather, but they also need to avoid becoming another bird's next meal. If they make the right decision, they live to see another day.