Crows,Ravens & The Science of Sleep

By Richard George

Crows roost in large, sometimes huge murders (a flock is called a murder) at night. A hundred years ago one could find these roosts just outside villages and towns, and it was thought they did this for safety from dogs, cats and owls that like to nest in human built structures. Now, however, these roosts are most often located inside the city limits and it’s thought for the same reasons as they roosted outside the city before.

Crows Choose to Sleep Inside City Limits

Inside cities are 5 – 15 degrees Fahrenheit warmer than the surrounding urban areas, and even where it’s legal to shoot crows, it’s illegal to fire weapons within city limits. Crows don’t see well in the dark, so sleeping in the city gives the advantage of being able to see a predator coming, and also the ability to see where to flee safely. In 1972 the Federal Migratory Bird Treaty Act of 1918 was written to cover crows, meaning crows are now much safer than ever before.

If one ever has the chance to see a large roost in the city before dark, it’s an interesting thing to watch. They begin to collect at the roost before dark and they all seem to chatter to each other and flit from tree to tree until it becomes the darkest. Then, they quiet down and sleep. Large roosts that are located just outside of city lights quiet down quickly, and those crows seem to get more sleep.

Some of the largest, oldest trees around are protected in city parks and privately owned land. These are large, old trees and are very attractive to roost-searching crows.
By Martin Cooper

Migratory Birds Have Reasons to Sleep in the City

Crows that are territorial also fly to the roost to sleep with family and friends at night, returning to their territory at dawn to begin foraging for their survival. Scientists think they do this for several reasons.

One theory is that, like humans at a hotel, many are meeting their needs of sleep and shelter while at the same place, at the same time, but they aren’t interacting with each other much. This doesn’t sound correct, especially if you’ve ever witnessed crows at such a roost. As mentioned before, it’s loud and very socially active until complete darkness.

There’s the old adage that there’s safety in numbers, and this may well be another reason they gather to roost together. A crow with many supporting helpers around may not be as attractive to a hunting hawk or other predator. And, there’s also the theory that they gather to spread information about food supplies and dangers to avoid.

Catching a Nap

Corvidae Daytime Behavior

During the day, some crows go off on their own to their territories and others may stay in a small murder and forage together. This is when you see a bunch of them swarm a yard or field and walk around while they hunt and talk together. They are loud and move through an area quickly and scientists believe this behavior is a social event, since crows do not depend on each other for day to day survival. Every now and then, they will catch a nap.

Written by Sandy Mccollum