For a long time, I used to say that crows like nothing better than pizza crust. But that’s not strictly true; crows seem to eat and to enjoy most table scraps. They don’t obviously roost near our house, but they must watch us because when we put out stale bread, old pasta, or anything else that’s edible, they descend within minutes. Sometimes you hear a call go out, and a group arrives; other times a single one arrives, but usually he’s soon followed by more. Often there are as many as 10 in our yard. We don’t tell our neighbors that rotisserie chicken leftovers are given to the birds.
I’m talking, of course, about the ubiquitous American crow (Corvus brachyrhynchos) here. They are large, fully black birds that range over most of North America. There are two other North American crow species that are virtually identical to the American crow but that have more limited ranges–Northwestern crow (Corvus caurinus), found in the Northwest, and Fish crow (Corvus ossifragus), found along the south Atlantic coast.
Crows are intelligent birds who have as many as 250 unique calls and make and use tools. They are highly social, live in close-knit family units, and are rarely alone. Crows take mates for life. They are highly adaptable and will live almost anywhere in natural or human-shaped environments, but they prefer open spaces or the margin of wooded areas; they don’t like unbroken forests or deserts. When not feeding from dumpsters or my backyard, they eat earthworms, insects, seeds, snails, small rodents, and song bird eggs and young. They eat most anything. They also help clean up road ways of smashed squirrels, rabbits, and whatnot; crows are not specialized as scavengers, though, and carrion is a small part of their diet.
I have always liked crows because they seem to have a strong sense of themselves and always seem to be having a good time. A group of them regularly gathers in my yard, sitting in various trees and calling to each other in their characteristically raucous way. I assume they’re swapping stories of food finds or maybe just wasting time.
A group of blue jays (Cyanocitta cristata) also gathers here. They too are social, intelligent, travel in packs, and seem to enjoy life. Jays too are omnivores and their choices in food and the source thereof is much the same as those of crows; so they’re competitors of crows. And they don’t like crows, and crows don’t like them. I often see groups of jays dive bombing the larger, less agile crows.
Sometimes, both crows and the jays will assemble and vie for our trees and lawn. They call to each other, likely insults and threats. When jays try to take a spot claimed by the crows, they are forced back. Then the same happens when the crows try an offensive. After a while, the conflict loses energy and individuals drift off until there’s no one left.
These crows seem to think my yard is theirs. Either that or they have a simple abiding hatred of turkey vultures (Cathartes aura) as well as jays. Twice a year turkey vultures migrate through in small groups, going south in October and back north in March. We have several mature Douglas firs that the vultures like to rest in and spend the night. If the crows discover the vultures, though, they go crazy, making a tremendous din, calling in reinforcements, and dive bombing the vultures; there will be as many as 25 crows. Finally, the vultures take wing, the band(s) of crows trailing after them. How far the crows follow I don’t know.
But not all is well with crows. West Nile virus, first identified in North America in New York City in 1999, is a threat to them as well as humans. The virus is effectively spread by mosquitoes, which carry the highest virus concentration in fall. Crows are very susceptible to it and were among its first casualties. So susceptible are crows that they function as a reliable biological indicator of the human disease potential.
In the initial onslaught of the virus and as it spread, crow populations were devastated–overall, somewhere in the neighborhood of 45% of the American crow was killed. A laboratory study showed that 97% of crows infected with the virus die. Another study of captured, live crows found that only 3% of those crows had antibodies to the virus in their blood, confirming that not many infected crows survive.
Nevertheless, crow is not considered an endangered species. Crow deaths from West Nile virus seem to be declining with time and the rates have leveled off. In some cases, crow numbers have increased. Nationwide, by 2006, surveys of crow numbers indicated only a 13% decline relative to 1999.
Several factors are responsible for these trends. Among them are increased resistance to the virus within crow populations and an apparent loss of virulence by strains of West Nile virus. But the most significant factor is probably the structure of crow society. Crows are among a small minority (about 3%) of birds and mammals that breed cooperatively. Their small family units include nonbreeding “helpers”. These are both young male and female birds who are generally offspring of the breeding pair and who contribute to caring for and rearing young. Helpers will delay moving away and starting their own families in response to the needs of their parental group. This intragroup cooperation provides a safety net for crows, without which the loss of one of the breeding pair would probably mean the loss of the entire next generation.
I know that some of my neighbors find the crows annoying. Crows make lots of noise, and they certainly cannot be considered “song birds”. On trash day, they tear open garbage bags and strew the refuse around, never picking up after themselves. But they also have a function as Nature’s garbage collectors, eating road kill and old pizza. They contribute to our well being by thinning the numbers of rats, mice, and rabbits that plague our homes and gardens. And they provide a consistent source of entertainment and theater in your backyards.