gulls

The number of ruffs in the Netherlands strongly declined during the years I was doing research on them. It was an unfounded suspicion that I had caused that. Nevertheless, it was not a good idea to proceed with the ruff project. Therefore, I started with something else. First, I tried to find out how behaviour was structured, how it could be programmed within an animal. The project was done with a few tame herring gulls that were held at the laboratory. Their behaviour during bathing and feather maintenance was observed in detail, and some attempts were made to influence it experimentally. The patterning appeared to be highly predictable. The picture above shows a herring cull, the picture below a black-headed gull that is preening its feathers. 

Bathing and preening gulls display a kind of routine with rigid sequences of activities that can scarcely be influenced by environmental factors. Their social behaviour is quite different. There is a lot of mutual interaction. They apparently communicate. In my next research project, that was done together with Gerard Baerends, Jan Veen and Ron Vodegel, animal communication became our main focus. We tried to work on this topic in a large breeding colony of black-headed gulls in the Lauwersmeer, a recently reclaimed area. The gulls were shocking for me after my experience with ruffs. There are hundreds of birds close together, males can hardly be distinguished from females and almost all individuals look the same.

Soon I decided to found my own colony in a large aviary in the backyard of the laboratory. The birds got coloured rings, and all individuals could easily be identified now. The gulls formed breeding pairs, built nests and laid eggs. They did not seem so monogamous as previously was thought. Some male gulls had more than one mate, some female gulls layed their eggs like a cuckoo in the nest of another, some male gulls preferred another male as a mate. Some years later, when parentage could be checked by means of DNA, it appeared that lasting monogamy is rather rare too in many other species of birds.

There were all kinds of possibilities for experiments in the cage. For instance, there were some trials with radio transmitters to record variations in hart beat frequency. This enabled us to relate behaviour to physical effort. The gull on the left in the picture below bears a transmitter on its back.

 

contact via e-mail: johan-van-rhijn@wxs.nl