What do cranes have for lunch?

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The crane is a species that fascinates us here at the RSPB. This magnificent bird survives in the UK in isolated pockets and is now the focus of a reintroduction project to get them back into suitable habitats in the UK. With all of the monitoring work that comes with such an important conservation project comes a number of questions. One question that is difficult to answer through observation alone is what do the cranes in the UK eat? A very difficult question to answer given that these stunning birds that dwell in remote places are very sensitive to disturbance. By watching them from distance in the wild makes it almost impossible to see what is being consumed. You can imagine the scene, a crane with its graceful long neck dipped down to ground level, hidden from view behind behind long grass and sedge.

This is where it gets messy! The intrepid RSPB conservation science staff monitoring the cranes were able to collect samples of the cranes faeces after they had left the areas of observation...(faeces, does 'poo' make it sound less grim?) and store it in ethanol for further analysis.

So between a brave volunteer, Helen, the crane presearch staff and I we have been spending a bit of time looking through these samples to find out what the cranes are eating. This subject matter is certainly not glamorous, it is definitely smelly, but it does come with plenty of interest and mystery, there are no records of anyone doing faecal analysis of cranes in the UK before.

We know that cranes eat a mixture of vegetable matter, grain and insects but we also know that they are opportunists, anything that can be swallowed could potentially end up on the cranes menu. The first thing we did was to separate what is what, we have six categories, vegetative pulp (the messy stuff!), fibrous plant material (bits of grass, reed and root), seed and grain, invertebrates, vertebrates and a category for unknown items (of which there will be a few!).

In total over 90 samples were gathered throughout the spring, summer and autumn. So far we have turned up some interesting finds. Probably the most surprising is the discovery of a field vole lower jaw, see the picture below. We can tell this is a field vole jaw by the fused together teeth, compared with mice for example that have more 'normal' teeth. Notice the grooves go all the way from the top to the bottom, in bank voles they only reach about halfway.

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Most of the other samples have so far shown to be dominated by vegetation with the occasional invertebrate. Helen found a 16-spot ladybird in one sample which must have been taken with a clump of vegetation!

I will post any more interesting findings that we come across, i hope you will enjoy these insights into our work!