Corvid bill morphology

There was a time when late April or early May would find me on the Outer Hebrides, Extramadura or eastern Poland (see here). This year I'm at Millet's Farm near Abingdon. While the children were petting lambs and the like, I noticed the local corvids appeared quite approachable, so I fired off a quick 250 shots of the local residents. On looking at the results I was really struck by the difference in bill structure between Rook and Jackdaw - check out the length of the Rook's bill, its monstrous!



These two species frequently feed in association and you would expect them to occupy different ecological niches, feeding on different prey items in different ways having evolved different skull and bill shapes in order to do this. If they were competing for the same prey items why would they associate? Some authorities have found that increasing bill-length, bill-curvature and sidewise orientation of the eyes is associated with an increase in the observed frequency in probing. If this were the case you would expect Jackdaws to have a smaller, less curved bill and more forward facing eyes. No doubts about the bill shape but do Jackdaws have more forward facing eyes than Rooks?

Looking good from here. All interesting stuff but I'm not sure I can spend another whole Spring in Cuddesdon, I feel the travel bug calling...