On the aims and methods of ethology.

In this paper Tinbergen defined Tinbergen's Four Questions, or complementary categories of explanations for animal behavior. that form the basis of ethology: Causation, Ontogeny, Survival Value, and Evolution. 

In 1973 the Nobel Prize in Physiology or Medicine was awarded jointly to Karl von Frisch, Konrad Lorenz and Nikolaas Tinbergen "for their discoveries concerning organization and elicitation of individual and social behaviour patterns."
See No.14138.
(Thanks to Juan Weiss for this reference and its interpretation.)