I filmed this extraordinary scene last Saturday showing an adult Herring Gull Larus argentatus apparently feeding on feather lice off the head feathers of another Herring Gull.
The video was taken at Katwijk aan Zee, the Netherlands on 14 November 2015 during high winds, from a distance of about 100 meters.
The scene had been going on for a short while before I started filming and it can be clearly seen that the gull is picking out objects out of the head feathers of the other gull. Surprisingly, the gull on the receiving end does not seem to mind very much. After a while though it does start to get annoyed and the feeding gull steps away, only to approach the receiving gull once more. When the receiving gull objects for a second time the feeding gull walks off…to try his luck with another gull. Extraordinary.
It is not allopreening
This is totally unfamiliar behaviour for me and after consulting with Dutch gull researcher Kees Camphuysen he also stated that he has never witnessed this before.
We both agreed that this is ‘simply’ fouraging behaviour with the gull taking advantage of an available food source, although it is difficult to understand what the nutritional value would be.
Large gulls are known for specializing in fouraging on specific food sources so this could be an extreme example.
At first glance the behaviour is very similar to ‘allopreening’: the mutual preening of feathers by a bonded pair of birds, commonly seen in Parrots and a few other bird species.
This however is not what is going on in the video: the receiver does not ‘enjoy’ the experience, there is no interaction between the two birds that indicates that they are related, and the feeding gull uses more than one gull as a ‘source’.
I would be very interested to hear about similar observations in gulls so please contact me when you have more information.
In the mean time, here is an interesting blog post about louse spots in gulls by Amar Ayyash.