I am an integrative behavioural and evolutionary ecologist studying the evolution of social behaviour and life history patterns in social animals, to discover why and how animals cooperate or compete. My research focuses on behaviour as this is the level at which organisms interact most directly with their physical and social environment. I integrate empirical and theoretical studies to obtain deeper knowledge of the evolution of adaptive behavioural responses. I focus on long-term studies of wild birds in naturally varying environments; these are complemented by experimental studies at the individual and local population levels (also on non-avian model systems). My first main achievement is that, starting in 1985, I established one of the most prominent model systems in evolutionary ecology: the Seychelles warbler. Warblers normally produce one chick per nest and can be cooperative breeders, in which more than two individuals are engaged in raising the single offspring. My work on Seychelles warblers (and other social systems) substantially advanced the advanced the fields of behavioural ecology and social evolution.

My research focuses on four groups of questions:

1. What drives the evolution of group living and cooperative breeding?^.

2. What drives the evolution of sex allocation?^.

3. Does sociality affect senescence?

4. Is social flexibility a powerful mechanism to cope with a rapidly changing world?

I publish regularly in the fields of evolutionary biology, behavioural biology, zoology, ecology, and genetics, but also in theoretical biology, biodiversity conservation, environmental sciences, immunology and endocrinology, and occasionally in psychology, molecular biology and medical science. I have published (and co-edited) two books on social evolution. Starting January 2020, I am a member of the Editorial Board of the journal Behavioral Ecology.