Dispersal Ecology: Stay or Leave?

contact persons: J. Tinbergen, J. Komdeur and C. Both

 

One of the most important decisions in an individual's lifetime is where to settle for breeding. Potential breeding places often differ in quality, and an individual should aim for a high-quality breeding site. But if all individuals compete for these sites, it is difficult to obtain such a site and failure may lead to forgo breeding altogether. The decision where an individual should try to establish its breeding place thus should also depend on what other individuals in the population are doing. This is called frequency dependence.

     Young individuals searching for a breeding site can do this close to home, and risk competition with their parents, siblings and neighbours, or disperse a certain distance and explore alternative (and potentially better) sites where competition may be lower. If a young has settled at a certain place and has bred successfully, it often stays there for the rest of its life. In most bird species young females disperse more than young males, and in some species also older females are not site faithful, but may breed during their life at very different locations. The consequences of a certain dispersal strategy do not only depend on the decision of the individual, but also on what others in the population are doing. If all individuals stay at home it is better to leave, and if everyone leaves, you rather should stay.

     We study social influences on dispersal and their fitness consequences in two different systems. One is an experimental manipulation of fledgling sex ratio and density in Great tits  Parus major in the Lauwersmeer area (northern Netherlands) and the other is on social status and helping in the cooperative Seychelles warbler Acrocephalus seychellensis on different islands of the Seychelles (in the Indian ocean).