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.