Gulls

The number of ruffs in the Netherlands strongly declined during the years I was doing research on them. However, I did not play an appreciable role in this decline. 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 near 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.

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, but, by evolutionary reasoning, some investigators rejected the idea that an individal shares honest information about its plans. On the basis of computersimulations we could invalidate their view. 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 was previously 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, in many other species of birds too, lasting monogamy is rather rare.


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.
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