They perch on branches and lamp posts, watching the people below them walking by.
When they spot something that catches their eye, like a plastic bag that could potentially carry food, they strike.
Flapping their big black wings, the crows swoop down on their targets, peck at their victims and startle them. This has been happening over the past few days, just outside Hougang MRT station. Men, women, children - no one is exempt.
About half a dozen crows began their attacks on Tuesday evening, reported Chinese evening daily Lianhe Wanbao.
When The New Paper visited the area on Wednesday at about 7pm, we spotted at least five big adult crows swooping down on unsuspecting people.
We followed some of the birds and were led to a small tree just outside Hougang Mall on Hougang Avenue 10, opposite Block 425. A few crows nestled in the tree while the rest perched on top of lamp posts.
We noticed that they would particularly strike at those carrying plastic bags walking near their tree.
In half an hour, seven people were attacked. All the victims did not see the crows flying down on them.
By the time they felt the crow's beak and the flap of its wings, the offending bird would have flown off.
While some people shrieked in shock, most were left puzzled and looking around before they hurried away.
A woman in her 20s was walking past the tree with a plastic bag of groceries in each hand when a crow flew down and pecked her head.
She started, spun around and immediately swung her plastic bag at the bird.
She said: "I'm okay. I was just shocked, that's all. Perhaps the crow was hungry."
Ms Aini Abdullah, 41, who works at a booth at the carpark near Hougang Mall, said the crows appeared in numbers on Monday.
"One afternoon when I was in the ticketing booth, I heard loud noises from the roof. When I came out of the booth to check, I saw many crows perched on top, pecking away at my roof. It shocked me," she said.
A biodiversity expert told TNP that the attacks could have stemmed from people feeding them.
Assistant Professor Frank Rheindt from the National University of Singapore's Department of Biological Sciences said the attacks were likely carried out by house crows, or Corvus splendens.
"What they're doing could be misinterpreted as them attacking people, but they may actually just be wanting to be fed.
"Like monkeys, they are incredibly smart and they are able to recognise plastic bags, which they think will have food for them," he said.
An Agri-Food and Veterinary Authority (AVA) spokesman told TNP that the AVA will conduct surveillance and crow control operations when it receives reports on crow attacks, to safeguard public safety.
These include tree pruning to deter the birds from roosting, properly disposing of food to deny the birds available food sources and bird control operations.
There were 260 crow-attack reports from the public last year, down from 460 in 2013.
When TNP visited the area again yesterday, we spotted six crows, although the birds did not attack anyone.
While most Hougang residents said they have not seen or experienced attacks by crows, some voiced their concern about the recent development.
Said Ms Cheryl Chong, 19, a student: "Of course I'm afraid. I didn't know this was happening. I take the MRT every day and I have to pass by the area."
Another resident, Ms May Lee, 23, a stewardess, said she may avoid the area near Hougang Mall for now.
"It is scary and it worries me to be walking on the streets now," she said.
The best thing for residents to do is to stop feeding these birds, said Prof Rheindt.
"Many people don't realise that feeding these birds with food scraps is a bad thing. Plus, what you are feeding them may not be healthy for them," he said.
BY THE NUMBERS
260: Reports of crow attacks by members of the public made last year, down from 460 in 2013.
WHAT TO DO WHEN ATTACKED BY CROWS:
Seek shelter immediately and avoid the area as it may be near their nest
Wave your arms or umbrella at the crows to scare them off
Use shiny objects to scare them off
Contact AVA at 1800-476-1600 or through its website
HOW TO PREVENT CROWS FROM GATHERING:
Keep your surroundings litter-free
Properly dispose of trash and keep trash bins covered
Clean up after feeding your pet as crows may look to scavenge leftover food
Crows 'opportunistic when it comes to food'
House crows are not native to Singapore.
They were brought here from India on trading ships in the 1940s to feed on crop pests.
Today, house crows have settled down and made the urban jungle of Singapore their home, said Assistant Professor Frank Rheindt of the National University of Singapore.
"But these birds are not considered a desirable part of Singapore's fauna as they were introduced into the ecosystem. They are not supposed to be here in the first place," he said.
Over the years, they have been able to survive and thrive in Singapore - becoming cohabitants of the human settlement here - because of their intelligence. For example, they make their nest at the top of trees where they will be out of reach to most predators, he said.
He added that crows have also been reported to use tools when finding food.
Mr Alan Owyong, the vice-chairman of the Nature Society (Singapore) Bird Group, said crows have also been known to attack larger birds, such as eagles.
"When they see an eagle carrying food in its talons, they will attack in a group knowing they have strength in numbers. The eagle, when harassed, will then drop the food, which the crows will pick up."
Crows, being omnivores, are also highly adaptable and eat practically everything, said Prof Rheindt.
"They feed on anything such as plants, food scraps and dead animals on the road. They are opportunistic when it comes to food," he said.
Prof Rheindt also said some crows may have grown used to people feeding them.
"That could be why they are swooping down on people, hoping to be fed by them."
The Agri-Food and Veterinary Authority said crows are also particularly protective of their young and may attack when threatened. They can also hold grudges and may attack if you have accidentally offended one of them.
This article was first published on January 16, 2015.
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