45.1 TINBERGEN’S QUESTIONS

We begin our exploration of animal behavior by asking a simple question: Why does an animal exhibit a particular behavior? The Dutch behavioral biologist Niko Tinbergen divided this over-arching question into four separate questions, each one focusing on a different aspect of the behavior. Let’s consider an example—Why does a bird sing? While apparently straightforward, this question can be broken down into more specific questions and then answered in a number of different ways:

• Causation. What physiological mechanisms cause the behavior? This question can have multiple answers. A bird sings because its hormone levels have changed in response to changes in day length. Or, more immediately, a bird sings because air passing through its specialized singing organ, the syrinx, causes membranes to vibrate rhythmically.
• Development. How did the behavior develop? Here the focus is on the role of genes and the environment in shaping the development of the behavior. In birds, typically it’s the male that sings, and he has learned the song from his father.
• Adaptive function. How does the behavior promote the individual’s ability to survive and reproduce? In this case, the answer to the question might be that a male bird sings in order to attract a mate and then reproduce.
• Evolutionary history. How did the behavior evolve over time? Complex bird songs may have evolved from vocalizations made by ancestors that were reinforced and became increasingly stereotyped or ritualized over time, so much so that we can often identify a bird species simply by hearing it sing. A behavior may have originated to fulfill a function different from the one it currently serves. For example, the song of a particular species may have first evolved to claim a territory but now is used to attract mates.

Tinbergen’s analysis allows us to see that different answers to the question “Why does a bird sing?” can all be correct. The first two, causation and development, are mechanistic explanations for behavior, whereas the second two, adaptive function and evolutionary history, provide evolutionary explanations of how natural selection has shaped a behavior over time. Tinbergen’s four questions are complementary ways of looking at the same problem, and are a good starting point for the analysis of behavior.