Ethology is the scientific and objective study of animal behaviour, usually with a focus on behaviour under natural conditions, and viewing behaviour as an evolutionarily adaptive trait. Behaviourism is a term that also describes the scientific and objective study of animal behaviour, but it usually refers to the study of trained behavioural responses in a laboratory context, and without a particular emphasis on evolutionary adaptivity.
Links
[1] https://hootsgo.org/?q=node/6362
[2] http://en.wikipedia.org/wiki/Ethology