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This is where I post various musings about wildlife and ecology, observations of interesting species (often invertebrates)
and bits of research that grab my attention. As well as blogging, I undertake professional ecological & wildlife surveys
covering invertebrates, plants, birds, reptiles, amphibians and some mammals, plus habitat assessment and management
advice
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main interests and key projects, and you can follow my academic work here.

Monday, 22 November 2010

Playing with cars - can crows make their own roadkill?

It is well known that carrion crows (Corvus corone) frequently feed from roadkill. As they lack a bill specialised for tearing into flesh, they may need a carcass to be opened by another animal before being able to scavenge – a job done very effectively by the impact of a vehicle.
In Japan, they have been seen to use cars to crack walnuts, placing them on pedestrian crossings when the traffic stops, and after traffic has passed, waiting for the lights to change again in order to collect the opened nut safely; if the nuts are missed, they even hop down and shift them (see video here) (Nihei 1995). This is astonishing behaviour, first noted in Japan in 1990, but in hindsight not that difficult to imagine developing – after all, crows already drop prey items such as molluscs onto hard surfaces to break them. As well as being an area where research has been undertaken (Zach 1979), I have seen this on a stony beach in southern England, and a road is a hard surface. From this starting point – (1) drop hard food onto the road, (2) notice and remember that cars aid the food-opening process, (3) learn to avoid the dangerous cars, (4) notice that pedestrian crossings have safe traffic-free periods handily announced by lights and bleeping, (5) adapt points 1-4 by moving nuts if necessary. So, most impressive, but it still follows from development of a well-known behaviour in a new urban setting.
However, what about roadkill? I am not aware of crows dropping unopened carcasses onto roads (though suddenly it seems plausible if the carcass is small...), but on two occasions I have witnessed what looked, from my human perspective, like a crow ‘herding’ a pigeon into traffic... could it be creating its own roadkill? Speculative, yes, but also plausible I feel. Of course, it could simply be aggression with the crow pushing the pigeon roadwards by chance, but as the pigeon moved back towards the grass verge, the crow did appear to be trying to prevent it. I didn’t see the pigeon being run over on either occasion, but still I have to wonder and on both occasion I had a witness who agreed what the event looked like... Now, all that’s lacking is some evidence, so any similar observations would be really interesting and much appreciated, or of course indications that I’m talking scribble!

References

Nihei, Y. (1995). Variations of behaviour of Carrion Crows Corvus corone using automobiles as nutcrackers Japanese Journal of Ornithology, 44 (1), 21-35 DOI: 10.3838/jjo.44.21


Zach, R. (1979). Shell Dropping: Decision-making and optimal foraging in northwestern crows Behaviour, 68 (1), 106-117 DOI: 10.1163/156853979X00269

4 comments:

  1. Fascinating theory.
    I wish these crows get on with it and shove more pigeons into the path of un coming car.
    Mind you, the day we finally manage to drive over one is well into the future. they are far too wily.
    I noticed you too have a bird sound linked to your blog. Mine is aark - aark, which looks like the transcript of a crow call. ??

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  2. I haven't seen this happening again since this post, but I will keep my eyes open...

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  3. I witnessed once this interesting behaviour (not in Great Britain, but in Germany). A group of three or four carrion crows were forcing a pigeon to land at a pavement. The crows drove their prey towards the road and prevented an escape. After a while, a car run the pigeon over.

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