Crows taking stones

[terryoc]

In work we have a "quad garden" which is covered with "pea gravel" stones. Over the last 4 weeks (before the snow) we have seen many crows (20 - 30 at times) picking away in the stones. This was going on for a few weeks. At first we thought they we searching for food under the stones - but on closer examination we noticed they are actually selecting stones of a particular size and taking them away. In my opinion I think these stones are too big to be swallowed for their gizzards. What other purpose would they have for such behaviour.

[Catherine]

Hi, Terry, if you 'Google' you will find this activity mentioned in several forums.

The consensus of opinion seems to be that they take them back to their nests as 'tokens' for their partners.

I suppose, since Magpies are Corvids too, and they are known to collect shiny items, it might just be possible!

[rolf]

They are Amazing birds, always found it amusing with Magpies and as Catherine says, Crows are endowed with a similar fascination.

[terryoc]

Catherine, I think there is some other purpose - they are just taking too many for tokens - how many tokens do their partners want? This work has been ongoing for 2-3 weeks by maybe 20 birds throughout the day. It has been suggested they might be trying to raise the water level in a some nearby water source.

[Catherine]

Well, if pebbles were diamonds....

I really don't know what the answer is, Terry. I just gave a possible suggestion.

There was one answer which suggested that the birds were raising a water level somewhere, but there was no proof.

In Aesop's fable, 'The Crow and the Pitcher', a Crow could not reach the water at the foot of the pitcher, so he used pebbles to fill the pitcher and raise the water level so he could drink. Whether that fable was based on something Aesop saw or not, we will never know!

Check what the Rook does in this video though;
YouTube - Rook uses stones to raise water level and get food 4

[terryoc]

Catherine,
An update from one of my colleagues when supports your "tokens" suggestion -obviously not very busy as he has plenty of time to study the habits of these crows. He noticed that as the sun hits the quad it dries out the stones - the crows move along towards the still shaded areas and go after the wet and shiny stones.
Terry