The main research interest of the research group Behavioural Ecology & Ecophysiology is the study of the causes and consequences of variation in behavioural traits among individuals. Most studies are carried out within an ethological framework, focusing on all four major aspects of animal behaviour: causation, development, function and evolution. We use an integrative and multidisciplinary approach to study reproduction and sexual selection in different animal groups, but primarily in birds. Whilst our core research is in behavioural ecology, our current research interests span physiology to population ecology. We combine work on wild populations of birds with controlled aviary and laboratory experiments. Recent work is focusing on (1) communication in different animal groups; (2) the function and evolution of bird song with particular attention to costs and constraints that limit the expression of song; (3) relationships between hormones, behaviour and life histories; (4) sperm competition and mating systems. We are also interested in the application of behavioural ecology to environmental and biodiversity problems. A recent line of research concentrates on the effects of heavy metals and persistent organic pollutants on the health and reproduction of birds and on the development of non-destructive methods of biomonitoring. We also study the conservation ecology of endangered fish species native to the Flanders using electrofishing techniques.