Behavioral ecology, or ethoecology, is the study of the ecological and evolutionary basis for animal behavior, and the roles of behavior in enabling an animal to adapt to its environment (both intrinsic and extrinsic). Behavioral ecology emerged from ethology after Niko Tinbergen (a seminal figure in the study of animal behavior) outlined the four causes of behavior.

If an organism has a trait which provides them with a selective advantage (i.e. has an adaptive significance) in a new environment natural selection will likely favor it. Adaptive significance therefore refers to the beneficial qualities, in terms of increased survival and reproduction, a trait conveys.

For example, the behavior of flight has evolved numerous times in reptiles (Pterosaur), birds, many insects and mammals (bats) due to its adaptive significance—for many species, flight has the potential to increase an animal's ability to escape from predators and move swiftly between habitat areas, among other things, thereby increasing the organism's chances of survival and reproduction. In all instances, the organism adapting to flight had to have "pre-adaptions" to these behavioral and anatomical changes. Feathers in birds initially evolving for thermoregulation then turned to flight due to the benefits conveyed (see Origin of avian flight); insect wings evolving from enlarged gill plates used to efficiently "sail" across the water, becoming larger until capable of flight are two good examples of this. At every stage slight improvements mean higher energy acquisition, lower energy expenditure or increased mating opportunities causing the genes that convey these traits to increase within the population. If these organisms did not have the required variation for natural selection to act upon either due to phylogenetic or genetic constraints, these behaviors would not be able to evolve.