RECENTLY, fairly early on a grey morning, I arrived at the river just in time to see a Crow (one of two or three in the vicinity) repeatedly flying low over the head of a Grey Heron (see photograph). Perhaps not surprisingly, the Heron seemed perturbed by this and often twisted its neck so that it was head-on to its attacker. In the literature there are references to ‘mobbing’/aggressive behaviour towards Herons by Crows (see e.g.,, including records of actual strikes on the back of the target Heron. Of course, Crows will behave similarly towards birds of prey. An interesting question is, why would they do this? Perhaps of relevance, although I didn’t realise it at the time, from my photographs I could see that this Heron had just predated something – and was in the process of swallowing it. I was too late to be able to tell what it was.

A number of possible explanations come to mind. ‘Mobbing’ usually refers to interactions between a predator and potential prey. I’m not sure the Crows would feel in danger of being preyed upon by the Heron, but perhaps, if they were intent on feeding nearby, they might feel some concern for safety. Or perhaps this is a ‘carry-over’ (a generalisation) from times, earlier in the year, when the Crows would be concerned with protecting their youngsters.

Alternatively, perhaps this behaviour is interspecific aggression, motivated by competition for resources. Crows often frequent this particular location (an island within the river) and feed amongst the stones. Although, I have also seen this behaviour in other locations, and ones that, as far as I am aware, aren’t particularly favoured by Crows for feeding.

On one such occasion a Heron was predating ducklings, much to the alarm of their mother. Again a crow was swooping over the Heron. So, could this be driven by altruistic behaviour on the part of the Crow - trying to discourage the Heron and help another species at a time of need? In this case, a difficult question to be wrestled with is - what would the evolutionary advantage of Crows developing/engaging in such behaviour? Another, less charitable possibility that has been put forward is that Crows behave in this way in an attempt to make the Heron drop, or regurgitate prey, so they can steal it (kleptoparasitism).

Of course, there may be more than one factor at play, here. It’s an interesting conundrum!