by Steve Westerman

Wharfedale Naturalists Society

CORVIDS are a common sight. This family of birds includes Crows, Rooks, Jackdaws, and Ravens, and also, perhaps less obviously, Magpies and Jays. Corvids are unpopular with many people because their food sources include the eggs and young of other birds. This has been a concern with regard to possible effects on declining farmland and garden bird numbers. Although recent literature reviews paint a nuanced picture.

By virtue of both their physical and mental attributes, these birds are able to take advantage of many different habitats and food sources. Along shallow parts of the river – at the edge or on little islands - Crows can be seen searching amongst the stones for food. They will turn stones in their efforts to find something nutritious. No doubt they find various small invertebrates. However, sometimes there are bigger prizes. I have seen one crow feeding on a crayfish and another feeding on a small fish.

During a walk along the riverbank, a few years ago, my brother drew my attention to a crow behaving unusually. The Crow was walking amongst stones on an island in the river – from where it would pick up something in its beak, fly upwards for a few feet, and then release the object (see photo), allowing it to fall on the stones below. The Crow then descended, apparently to view the outcome of its efforts. It’s impossible to be sure what was happening. There are many examples in the literature of birds dropping items onto the ground to access food within. Crows will do this to crack open mussels and nuts, Gulls do the same with mussels, and so on.

Is it possible that this bird was trying to open the shells of molluscs? Unfortunately, my photographs were not sufficiently detailed to be sure, and in some photographs (although perhaps not this one) the objects did look a little like stones. Could it be that the bird was dropping stones on something below in order to break that? The moment of object release didn’t seem sufficiently controlled or considered to support that conclusion. I suppose a further possibility is that the bird was experimenting – i.e., it was finding out whether dropping different objects would reveal food inside. I’m not sure what the answer is – but it was an interesting behaviour to see, nevertheless.

Taking ‘shell-cracking’ strategies an ingenious stage further, in Japan Crows have been observed dropping nuts on roads in order that the passing traffic will run over them and allow access to the contents (a BBC Studios clip of this behaviour can be found here: www.youtube.com/watch?v=BGPGknpq3e0).

www.wharfedale-nats.org.uk