You're walking along, minding your own business, when thwack: you're hit from above to a flurry of wingbeats. From your defensive crouch, you catch a glimpse of an inky black shape banking into the trees.

That's the bewildering – and sometimes bloodletting – experience at least 15 people endured last month on the campus of the Cork Institute of Technology (CIT) in Ireland: they'd been strafed by crows.

Well, better get this out of the way: cue the obligatory clip from The Birds. (Still freaky after all these years).


The CIT crow strikes – some of which resulted in tetanus jabs and antibiotics for the victims – got plenty of local media attention, and had officials at the college warning people to avoid affected areas of campus.

So why the angry birds? Some guessed that with campus mostly empty at the close of the spring term, the crows had lost a prolific source of food scraps from students, making them just a little disgruntled. But another theory suggested the birds were simply defending a nestling that had tumbled to the ground.

The latter explanation got more credence when the team from the Cork Society for the Prevention of Cruelty to Animals (CSPCA) arrived on campus to investigate the avian assaults. Within the "strike zone", CSPCA officials found a grounded nestling – a jackdaw, to be exact, a small crow widely distributed in Eurasia. They nicknamed the little squirt "Jack" (makes sense) and placed him in foster care, as the team was unable to locate his nest.

baby jackdaw_2017_06_15.jpg
Jack the jackdaw. Image: CSPCA/Facebook

Multiple newspaper stories called the campus crow strikes "bizarre", but that's not altogether accurate. Given how extensively humans and crows overlap, attacks by the birds are indeed uncommon, but they do happen predictably – and Cork's definitely not alone. (Just have a look at this interactive map of crow attacks in Vancouver and Victoria, British Columbia.) In the Northern Hemisphere, this is prime time for dive-bombing crows.

To learn more about this disagreeable (but ultimately perfectly understandable) facet of corvid behaviour, we checked in with Loma Pendergraft, a masters student at the University of Washington who studies crow cognition and social behaviour.

He confirmed that defence of a fledgling best explains the CIT crows' aerial crusades against seemingly innocent passersby. A shortage of student-supplied food scraps did not jibe with how the birds behaved: hungry crows that associate people with snacks confront us in quite a different way than antagonistic birds trying to drive us away.

Crows seeking a handout, for one thing, might tap a person with their feet, but don't typically initiate the more painful beak-on-flesh contact. What's more, birds guarding a fledgling will harass any perceived threat in the vicinity, whereas a crow with an appetite is likely to pester somebody who's fed it in the past. 

crow attack_2017_06_19.jpg
Hungry crows that associate people with snacks confront us in quite a different way than antagonistic birds trying to drive us away. Image: Fabiano Kai/Flickr

"Aggressive crows will attempt to stay out of view," Pendergraft added via email. "They'll perch high and fly around constantly, whereas the hungry crows will deliberately remain in the person's field of view when possible – they are hoping to be fed." 

In fact, conditions for an actual assaultive strike are pretty specific, according to Pendergraft. "I would only expect crows to physically harm a person if they are defending their offspring or mate," he said. "However, if the victim has a strong negative association ... then the mob could get big and energetic enough that the crows might start dive-bombing." 

While panhandling birds usually keep quiet, defensive ones caw a lot. The cacophony crows unleash when they're trying to encourage us (with sharp, prodding beaks, if necessary) to exit the scene might sound like abuse targeted at the enemy, but Pendergraft says it's more likely that these are crow-to-crow rallying cries: "We believe that the calls given by mobbing crows serve two purposes: recruit additional crows to strengthen the mob, and warn naïve crows about novel sources of danger."

Whether it's a food-giver or perceived marauder, the ability to recognise a particular person is just one of the remarkable cognitive abilities crows possess, endowed as they are with a hefty forebrain and complex social behaviour reminiscent of dolphins or primates.

Crows' ability to distinguish between faces was tested by recording how the birds reacted to mask-wearing researchers. The results showed that the crows not only remembered faces, but also how each masked human treated them. Image: Marzluff Lab/U of Washington

Some fascinating and high-profile research out of the University of Washington lab run by Pendergraft's advisor, Dr John Marzluff, has demonstrated just how savvy crows are at communicating danger – and how acutely they seem to observe human beings, whose suburbs and cities they've taken to with gusto.

For example, crows remember the faces (er … creepy latex masks) of persecuting humans and convey that knowledge amongst themselves and down generations; they cue into humans making direct eye contact with them; and they gather around their dead and appear to derive negative associations from the setting (and from human beings near the crow-corpse).

Nightmarishly masked biologists aside, humans usually fall on the crow threat radar only during nesting and fledging season: attacks of the sort seen at the Cork campus tend to wind down by early to mid-summer, once young birds have fledged out.

Birds of prey, by contrast, ring year-round alarm bells. Certain birds of prey, that is: crows will enthusiastically mob and dive-bomb red-tailed hawks and bald eagles, but rarely respond that way to ospreys, which look superficially similar but (unlike the first two) don't have an appetite for crow.

This is true, anyway, where crows regularly encounter ospreys. One study used taxidermy osprey mounts to compare the reactions of crows accustomed to seeing the "fish hawks" around to those residing in osprey-free habitats. Crows in the former group mobbed the raptors less often than those in the latter group, for whom the mount represented a novel potential threat.

Among the osprey-accustomed population, the researchers would occasionally observe a single crow – likely a younger, inexperienced individual – assailing an osprey mount and drawing in other crows with its calls.

"But the arriving crows would simply sit quietly before leaving after a minute or two," Pendergraft explained. "This suggests that while mobbing can teach naive crows about danger, the opposite is also true – the lack of response from other birds can habituate nervous crows to safe situations."

A flock of crows "encourages" a bald eagle to leave the area. Via MyBackyardBirding/YouTube

Such insights into corvid perception and communication are all well and good, but how about some practical, on-the-ground tips for fending off a defensive crow assault?

Pendergraft happens to have a useful write-up on the subject over at his website. His basic boiled-down advice? First and foremost, leave the area as quickly as you can, and try brandishing an umbrella and/or facing the attacking bird, who should be leery of making a head-on strike.

And if you chance upon a scruffy baby crow on the ground this time of year – not an uncommon occurrence – the best course of action is to leave it be. As Kaeli Swift – another Marzluff grad student currently investigating death among crows – notes in this blogpost, you'll most likely do more harm than good trying to "rescue" such nestlings or fledglings.

And remember, while your average "crow attack" may simply reflect a concerned parent trying to protect its offspring, nothing's stopping you from indulging in some killer-bird fantasies with a bowl of popcorn and some classic Hitchcock.*

Incidentally, The Birds does have at least a little toehold in reality: Alfred Hitchcock partly based his thriller on a 1961 incident in which hundreds of seabirds – mainly sooty shearwaters – basically went nuts in the coastal California town of Capitola. Many scientists now suspect these birds were suffering from paralytic shellfish poisoning, caused by an algal toxin.