Behavioural ecology is the study of how behaviour is influenced by natural selection in relation to ecological conditions. It is a relatively new field – about 40 years old – to which I have been an enthusiastic contributor for 30 years. During this time behavioural ecology has grown in popularity, empirical richness and theoretical sophistication. Around the world, behavioural ecologists are employed in universities, conservation organisations and government agencies; they have been elected to national academies of sciences, and received prestigious prizes (Crafoord, Cosmos, Kyoto); at least a dozen scientific journals publish articles on behavioural ecology; and the biennial meeting of the International Behavioral Ecology Society regularly draws more than 1000 participants.

Why is behavioural ecology so appealing? For me, a curious naturalist, it is the challenge of asking new questions, the fun of addressing them using the theoretical framework pioneered by Darwin and embellished by Williams, Hamilton, Maynard Smith, Trivers and Dawkins and the empirical approaches pioneered by Tinbergen, Lack and Goodall, as well as the deep satisfaction of cracking an unsolved puzzle – at least occasionally. For example, in my case, why do bank swallows breed colonially, why do Belding's ground squirrels give alarm calls and how do they recognise half-sisters, why do wood ducks lay multiple parasitic eggs, why do queens of many social insects mate so frequently, why do naked mole-rats live like eusocial insects, and how have bdelloid rotifers survived and speciated without sex for 40 million years?