Why Do 1000’s of Crows Roost in Town?

Three American crows (photo from Wikimedia Commons)

10 December 2023

When 20,000 crows come to Pittsburgh for the winter, they have to sleep somewhere and they inevitably make a mess. Why do they roost near us where the mess will get on our nerves? Why don’t they sleep in the woods? Let’s take a look the reasons crows choose one location over another when it’s time to sleep.

Crows have a few simple requirements for a roost and they all have to come together at the same place. Safety is a big one. Crows want:

  1. Tall trees for roosting
  2. Warmth when it’s cold
  3. No great horned owls!
  4. Safety in numbers
  5. Night lights. Lots of them.
  6. White noise at the roost
  7. No harassment from humans

1. Tall trees for roosting: Crows prefer to roost at the very top of mature trees. They perch on the highest twigs that support their weight.

Crows coming to the roost, Pittsburgh, 2017 (photo by Sharon Leadbitter)

2. Warmth when it’s cold: When the weather is well below freezing trees are too exposed for a good night’s sleep so crows may choose rooftops instead. Cities are warmer than the surrounding countryside due to the urban heat island effect.

Crows on the roof (photo courtesy Crows’ Call at University of Washington, Bothnell)

3. No great horned owls! Crows are terrified of great horned owls who can hunt them in the dark. They prefer places that great horned owls avoid.

Great horned owl (photo by Alan Wolf via Flickr, CC license)

4. Safety in numbers: Crows sleep in a crowd so that someone’s always awake to watch for owls. It also lowers the odds of an individual being eaten.

Crows asleep near Heinz Chapel by the light of the Supermoon, Dec 2017 (photo by Kate St. John)

5. Night lights. Lots of them: Crows like to sleep with the lights on. It’s easier to watch for owls when you can see them coming. There are no nightlights in the woods.

Crows in a tree on Thackeray Ave, Pittsburgh, 2011 (photo by Peter Bell)

6. White noise at the roost: In addition to night lights, crows want white noise at the roost(*), the sound of running water or traffic. This location along Fifth Avenue at the University of Pittsburgh combines all their requirements in one place. Except that the mess bothers humans.

Crows roosting along Fifth Avenue in the trees at Pitt, Dec 2017 (photo by Kate St. John)

7. No harassment from humans: The perfect roost is usually near humans but crows make an enormous mess that people have to clean up. When the crows wear out their welcome, people figure out ways to get them to leave. This includes loud abrupt noises such as clappers and bangers, flashing lights, and harassment by falconers’ birds.

Clappers used to disperse crows (photo courtesy Alex Toner, Univ of Pittsburgh)
screenshot from video Falconry moves the crows in Portland, OR

Now that we know what crows want at a roost we can figure out where they’re likely to be. Convincing them to leave is much easier to do before they land. 😉

(*) p.s. Why do crows want white noise when they sleep? No one has explained it but I have a theory that great horned owls avoid white noise. Owls need to hear their prey when they’re hunting and white noise makes that impossible.

4 thoughts on “Why Do 1000’s of Crows Roost in Town?

  1. For the last week or so, crows have been roosting between Sutherland Hall and the VA Hospital along Allequippa Street. It seems as though they have moved on from the area by the Cathedral of Learning.

    1. Although I should add that I didn’t see them tonight, so they have probably gone to a new spot now.

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