“Externally visible activity of an animal, in which a coordinated pattern of sensory, motor and associated neural activity responds to changing external or internal conditions" (Beck et al. 1981)
“A response to external and internal stimuli, following integration of sensory, neural, endocrine, and effector components. Behavior has a genetic basis, hence is subject to natural selection, and it commonly can be modified through experience" (Starr and Taggart 1992)
“Observable activity of an organism; anything an organism does that involves action and/or response to stimulation" (Wallace et al. 1991)
“What an animal does" (Raven and Johnson 1989)