A murder of wart-covered crows startling folks along Victoria’s Dallas Road might sound like the plot of a low-budget Halloween flick – but these eerie-looking birds aren’t the result of special effects, but of Mother Nature at her most gruesome.
The unsettling sight is caused by avian pox, a viral disease that produces crusty, wart-like nodules on featherless parts of a bird's body, such as the face, legs and feet.
While the birds may look like horror-movie extras, wildlife experts say the condition is not uncommon.
“It’s alarming to see, and you feel badly for the birds,” said Wallis Reid, senior wildlife rehabilitator at BC SPCA’s Metchosin-based animal rehab centre, Wild ARC. “But it is something we normally see each year.”
Reid said reports of infected birds have been rising in recent weeks, spurred in part by photos posted to Field Naturalists of Vancouver Island Facebook group, showing crows with visible lesions congregating along Dallas Road.
But according to Reid, this is normal for the time of year.
“It usually occurs after the breeding season, when immature birds are dispersing and congregating,” she explains. “Immature birds are more susceptible to infection because their immune systems are still developing.”
Despite the increase in reports, Wild ARC has not seen a rise in the number of admissions. “We usually only get a handful of birds coming in with avian pox each year,” says Reid.
That’s because most infected birds can still fly, making them difficult to rescue. “A good sign that the bird needs help is if it can be contained,” Reid says.
Avian pox becomes a risk to a bird’s survival when lesions compromise its vision or ability to feed or walk.
“It can also cover their airways and interfere with breathing,” explains Reid. “The lesions can also develop secondary infections that can affect their health as well, because it degrades the skin.”
In these cases, when a bird has been contained, Reid advises calling Wild ARC for advice and assistance at 855-622-7722.
However, in most cases, the bird will eventually recover.
“Sometimes it's just a very mild case and it goes away eventually,” said Ann Nightingale, volunteer and board member at Rocky Point Bird Observatory (RPBO). “Most birds that get it will recover from it."
A member of the Canadian Migration Monitoring Network since 1994, the RPBO catch and band around 7,000 birds a year. “And I would say that we probably see fewer than 20 cases of avian pox a year,” says Nightingale. “So it’s pretty uncommon."
Spread of the disease is most likely in areas where birds congregate or within close-knit groups, which Nightingale believes could be the reason for the spike in cases among Victoria's crows, as they gather in large numbers to roost.
"It doesn't spread quickly through the wild populations unless the birds are confined into a very small area," she says. “We see it most often with birds that associate quite tightly with other birds, usually of the same species, because it is contagious like any other virus."
Nightingale suggests keeping backyard feeders and birdbaths clean to help reduce transmission among birds.
“But if you see it on birds at your feeders, then this is an indication that it might be time to take feeders down for a little bit,” says Nightingale. “So that the birds disperse for a while, and it isn't being spread at your feeders.”
As for the risk to humans from the Dallas Road 'zombie' crows, there is no ‘caws’ for alarm.
While commonly spread by mosquitoes, avian pox cannot be transmitted to humans. “It’s not zoonotic,” confirmed Reid.
