Crows are sneaky little bastards. That appears to be the conclusion of a study recently published in The Auk: Ornithological Advances.

Researchers sifted through 2,000 US-wide incidents of bird-on-bird violence involving ravens and crows that had been collected and submitted to a site called eBird. In 97 percent of cases, crows were the aggressors. 

Not only are crows almost always the instigator of the fight, when they attack they attack in a group.

Ravens look similar to their corvid cousins, the crow, but they are roughly three times as big. This size and weight disparity would make one-on-one action an absolute no-no, at least as far as the crow is concerned – it would almost certainly be a lost battle. Instead, they attack dirty, approaching their more solitary rival in a tight-knit group of two to five individual birds. This is called mobbing.

Mobbing is an anti-predator behavior that several species of bird partake in, albeit in different styles. The majority of bird species target their rivals in larger, more disorganized groups. Activities may include squawking, dive-bombing, and defecating on their adversary. 

Importantly, this shows that when it comes to fights, size doesn't always matter. 

“In nature, when you look at aggressive interactions between species, usually the big guys beat up on the smaller guys,” said Ben Freeman, a postdoctoral researcher at the University of British Columbia, Vancouver, and a former Cornell graduate student.

"We show that bigger birds do not always dominate smaller birds in aggressive interactions, and that social behavior may allow smaller birds to chase off larger birds,” Freeman added in a later statement.

The researchers believe these attacks, although sneaky, are not entirely unprovoked and could be a preventative measure to protect the crows' offspring.

The truth is, ravens aren't exactly innocent victims in all this. While, on the whole, they elect to leave the adult crows well alone, ravens are quite happy to prey on a crow's eggs when the hunger strikes. This hypothesis is backed up by the observation that most cases of crow-on-raven aggression take place during breeding seasons. As for the attacks that take place in the winter time, the researchers suggest this could be a case of the crows taking pre-emptive action.

As well as providing intriguing insight into the lives of birds, the study highlights the effectiveness of citizen science. 

"This is a case example of the power of citizen science," said Freeman. "It would be next to impossible for even the most dedicated researcher to gather this data across North America. But because there are thousands of people with expertise in bird identification and an interest in bird behavior, we can use data from eBird to study behavioral interactions on a continental scale."