Tinbergen's Four Clauses

Mechanism
The physiology behind a behavior. This could be what stimuli produce a behavior or the specific physiological traits that produce the behavior.


Ontogeny
The development of a behavior over the organism's lifespan. This questions look into whether a behavior is learned from observation of other animals participating in the same behavior or is an innate behavior that the individual is born knowing.


Adaptive Value
How the behavior functions to increase the individual's lifetime reproductive fitness. This can demonstrate the evolution of traits that have produced a behavior (natural selection) that is more likely to increase fitness for an individual.


Phylogeny
The evolutionary history and development of the behavior. This question relates to how a behavior appears across a phylogenetic tree and how it can occur in other species through independent evolution or coevolution.