Note: Each year about this time, this city鈥檚 crows are on full alert as their babies learn to fly. The parents of these fledglings take their job as protector extremely seriously, dive bombing any pedestrian or cyclist who happens to be within feet of these baby birds.
In 2010, reporter Sandra Thomas sought the advice of experts after she and her partner frequently interacted with a pair of crows dubbed 鈥淐arl and Cindy Cawford,鈥� which for years ruled the property they shared. With fledgling season in full swing and stories of dive bombing birds becoming something of urban legend, it seemed fitting to run the story, first published on Aug. 27, 2010, again.
Last summer, as we sat around the patio table enjoying cool drinks and snacks, a small rock dropped from above barely missing a glass.
We all glanced skyward but saw nothing until a second small stone fell onto the table a few minutes later. Then we saw Carl, our resident crow, swoop past.
Although Carl's nest was in the front of the house, the large black bird would get agitated if we entertained more than one or two guests on our back deck. On this particular evening, Carl made his displeasure obvious. Since dropping rocks on us failed to move the crowd indoors, the crow perched just above our heads on the eaves of the house and cawed loud and long.
Courier readers have sent in similar stories about their relationships with the funny, cranky, smart and sometimes friendly birds living around their properties. To better understand crows, the Courier turned to University of B.C. zoology professor Wayne Goodey, an expert in the behaviour, evolution, conservation and human impact on birds, animals and fish.
Goodey says the Northwestern crow (Corvus caurinus) that populate 麻豆传媒映画belong to the Corivade family of birds, which also includes jays and rooks. Northwestern crows are typically between 40 and 45 centimetres in total length, with a 70 to 80-centimetre wingspan. Adult crows typically weigh between 300 and 340 grams.
"That family is probably the most intelligent of all birds and are comparable to parrots when it comes to being smart," says Goodey. "Most birds are not that smart."
live in extended family groups with complex social orders revolving around a mature breeding pair, much like local Steller's jays, Goodey explains. Crow families typically include offspring, siblings and non-mating adults and grandparents. "
The non-breeders and hangers-on just congregate around them," says Goodey.
Like cats and dogs, crows can include humans in their social circle.
"My cat includes me in its social circle, but that's pretty much because I'm adjacent to the food cupboard," says Goodey. "Those animals by nature have social tendencies."
Crows are also smart enough to learn and be trained. Goodey wasn't surprised to hear that before his death Carl would often come when called.
"They're sharp and they pick up sounds so they begin to recognize that sound," says Goodey. "It's not even so much about the reward [of food], but the fact they know that when they come nothing negative is going to happen to them."
According to a University of Washington zoologist who was interviewed in a recent Macleans magazine article, crows have good memories and can remember faces. When they attack, as they're known to do during fledgling season, individuals should keep moving so the birds can't remember their face.
Goodey says that might be the case in rural areas where crows come into contact with a limited number of people.
"But in the city they could see hundreds of different people in a day," he says. "In local cases where they mainly see the same people they might be able to pick a person who's threatened them."
Goodey estimates there are about 100,000 crows living in Greater Vancouver. The large number is thanks to the abundance of available food and lack of raptors, such as hawks, which is a crow's largest predator next to the great horned owl. Breeding pairs can produce two or three sets of babies per season, but their survival rate is low and many will die within their first year.
While crows mate for life, it has nothing to do with love or a sense of commitment, the zoologist says. One Courier reader wrote to say that when one of the crows living near her home was killed, its mate wouldn't leave the body until dark.
"People have this romantic idea that when birds mate for life it's a special bond," he says. "But it's really just about what works for them. What benefit is it to them to wander if they're having success with the mate they're with."
Locally, crows roost at night in a concentration of large trees near Grandview Highway and Boundary Road, stretches along Still Creek in Burnaby and in Pacific Spirit Park. A large flock of crows is called a murder. Goodey assumes some crows also roost in Stanley and Central parks. Construction is not a deterrent to roosting as heavy machinery typically isn't operated at night.
"They are quite habituated to human activity anyway," says Goodey, "so not likely to be driven away just by excavation or new buildings unless trees were removed."
By day, crows have a defined area or territory where they hunt and eat and eventually nest and breed. During nesting season, it's only birds too young or too old to breed that make the trip to roost.
Not everyone likes crows, and the Courier annually hears from readers calling for a cull of the "nuisance" bird.
Reader Emilie Sion wrote to the city recently complaining about crows and asked if a cull could be an option to control their population.
The Arbutus resident appreciates how intelligent crows are, but says several recent incidents have turned her against them. This spring, Sion's daughter had a nest of robins in her backyard until a crow landed on a nearby utility line and systematically killed and ate each of the babies, much to the family's horror. Sion says because crows are so smart they're dominating the landscape and winning out over small song birds.
According to Goodey, despite a crow's robust defensive behaviour around its own nest, they do eat the young of other birds.
"It would be wrong to say that they are nest predators in any specialized way, better to say they are opportunistic," says Goodey, who notes squirrels are equally guilty of attacking nests, something that's often not reported.
He explains any animal, crow or other bird, includes items in its diet based on availability and abundance, ease of collection and nutritional quality, not human concepts of morality.
"It may seem horrific to your readers when they think of all those eggs and nestlings being torn apart, but many are fed to equally cute and or deserving baby crows. And very few newborn birds, especially of smaller species on which crows might prey, are going to survive to adulthood," says Goodey. "Is it worse to have nestlings eaten or for them to starve or freeze to death? Nature isn't at all a nice place--this is simply the reality of natural selection in action."
Sion says because of the crow's appetite for nestlings, instead of small song birds we now have flocks of black birds in Vancouver.
"I wrote to city hall and got a reply to the effect that crows are migratory birds and they have no jurisdiction over them. They refuse to take action," Sion says. "At one time in 麻豆传媒映画crows were culled. The mayor is so focused on making 麻豆传媒映画a 'green city,' by way of the bicycle, he cannot see that flocks of crows are a sign of degradation. Mumbai is hooded-over by crows."
According to Connecticut-based Michael Westerfield, culls are ineffective at controlling crow populations. Westerfield founded the Crows.net Project in 1998 to study the American crow.
The project's focus is to prove the crow is a highly intelligent species with a fully developed language and culture. Westerfield, who's also studied anthropology and archeology, is a marine biologist, but told the Courier he found crows much more convenient to study than migratory fish.
Westerfield says except for size, there's little difference between Northwestern crows and the American species.
"The main difference between Northwestern crows and American crows is that yours tend to be more social with each other, more likely to live closer together and hang out in larger groups," he says. "Crows have a unique reproductive strategy that virtually guarantees that their populations can survive almost any catastrophe, including the continual attempts of humans to reduce their numbers because of perceived harm to agriculture or human health, or simply because they are thought to be a nuisance."
Some drastic measures were taken to reduce crow numbers in the past in the U.S., including the widespread use of poison and the destruction of winter roosts by a number of means, including dynamite, Westerfield notes. In one case reported in the March 25, 1940 issue of Life Magazine, the Illinois State Department of Conservation killed 328,000 crows in roosts with the use of "festoons of dynamite bombs."
"None of this has worked and the population of crows on this continent is perhaps as great as it has ever been," Westerfield says. "Even populations recently ravaged by West Nile virus seem well on the way to a complete recovery."
Crows are successful in overcoming major lethal events because, in general, they only reproduce when a mated pair successfully finds and occupies a territory, which may represent anything from a few suburban blocks to a fairly sizable area of woodland.
There are far more crows than there are available territories and this results in the majority of crows having to delay breeding until they are fortunate enough to acquire a territory that has for some reason become vacant. Although most crows are capable of breeding at one year old, most have to delay mating for two or more years.
"And, I expect some must never acquire a nesting area where they can reproduce," Westerfield says. "Some of the unmated crows may stay with their parents for a year or more helping out around subsequent nests, but the majority of them are 'floaters' who travel around and join up with numbers of other unattached crows to form temporary flocks or gangs for feeding and general socialization."
The result is a vast reserve of unmated crows available to take over and fill the gap left by mated pairs that may be culled, by occupying their vacant territory. Also, since it's common that the most obvious groups of crows are the unmated "floater" gangs, they are the ones most likely to be killed by municipal exterminators.
"Of course you can kill any number of these non-reproducing birds without making anything but a temporary dent in the area crow population," says Westerfield.
Finally, since the continent has large crow populations, if one area were to actually succeed in wiping out its crows, the neighbouring populations would simply expand to fill the vacuum. This played out in the case of the West Nile virus, which wiped out entire crow populations in some areas in the first years of the millennium, only to have them completely repopulated within several years, Westerfield says.
"As far as I can tell from reviewing a number of municipal crow removal efforts, some cities have indeed succeeded in moving large winter roosts from one area to another," he says. "But no one ever has succeeded in a planned attempt to significantly reduce the size of a crow population for any length of time in more than a very small geographical area. This being the case, most if not all attempts at culling crows are simply futile exercises in meaningless slaughter."
Whenever the idea of a crow cull is floated in the media, Courier readers vehemently opposed to the bird's elimination make their views known.
West Side resident Marie Decaire told the Courier earlier this month that she and her family enjoy the company of their resident crows. Despite the crows, small birds thrive in her neighbourhood. "In fact, there is a small flock of chickadees that visits our apple tree every day while Mr. and Mrs. Crow stand watch from our roof top," she says.
In the fall, Decaire adds, chestnuts fall from the trees lining the family's street and the crows wait for the nuts to be crushed by cars before flocking to feast on the meat.
"We love to watch them. They are very intelligent and full of funny antics," says Decaire. "We would certainly raise our voices in protest should anyone try to cull them. I suppose some might think them noisy, but they have never kept us awake. I would be much more concerned should the neighbourhood lose their resident crows. Remember Rachel Carson's Silent Spring?"
VIDEO: Gifts of the Crow by John Marzluff and Tony Angell
