Studying Crows | PCSPECIALIST

Studying Crows


When I lived in Bournemouth several decades ago there was a constant problem of dead crows on the fast dual-carriageway into Bournemouth from the A23. There's a lot of road-kill on that road of course and it's lined by tall fir trees so it's no surprise that it attracts a sizeable crow population.

The local council were just becoming aware of their environmental responsibilities back then, so they commissioned an ornithological behaviourist to see whether there was anything the council needed to do to the road, speed limits for example, or to the trees either side in which the crows nested in order to prevent so many crows from dying.

The ornithological behaviourist studied the crows and the traffic patters on an off for just over a year and there were regular updates on his studies and findings in the local newspaper. He became very familiar with the crows after a few months and claimed he could recognise almost all of them on sight, he even gave some names. I don't remember them all, but TwoClaw was one, because he only had two claws on one foot, and HookBill, because he had an over large upper beak, but there were others. He would include photos of many of the named crows in his newspaper updates.

One major discovery he found, that he didn't think had previously been observed in crows, was that when feeding on carrion they would station four, or sometimes five, 'sentry' crows around the feeding group to warn of approaching predators or other dangers. Because he was able to identify most crows on sight by this time, he was able to tell that the 'sentry' crows changed every time the group descended to feed.

He spent some weeks trying to identify a chief crow who was directing which crows would serve as 'sentries' each time the group descended but he was unable to find any evidence of a controlling bird. The crows just seemed to know that it was their turn to act as a 'sentry' and there was never any shortage of 'sentry' birds every time the group descended to feed.

Fairly soon after he realised they were using 'sentry' crows he was able to pinpoint the reason for the increased number of dead crows; sometimes the 'sentry' crow didn't give a warning of an approaching vehicle soon enough for the group to take to the air and one or two were struck and killed. To find out why, for several Sundays we had one or other carriageway closed whilst they measured at various points from crow eye-level, to see how far the sentry crows could see. The council were interested to see whether there were undulations in the road that from crow eye-level meant they couldn't see approaching traffic.

One thing they were keen to find out was whether the crows that were struck were being surprised by low profile fast sports cars. It was thought that the 'sentry' crows might not see them soon enough to give an adequate warning, especially if there were undulations in the road that hid them from the 'sentry' crow's point of view. Trucks were not considered to be a problem because of their extra height making them visible for some distance, plus they were generally slower than the cars.

Although there were some undulations found in both carriageways none of them were severe enough to prevent the 'sentry' crows seeing even the smallest sports cars soon enough. Plus of course, even with a late warning for a sports car the feeding crows didn't have to ascend very far in order to be clear of it.

The breakthrough came when the ornithological behaviourist studied the calls the 'sentry' birds were using to warn of approaching danger. It was found that all the crows were able to say "car" but none of them could say "truck".....