The problem of vigilance in animal life.
D000819:Animal Communication; D000818:Animals; D001143:Arousal; D001288:Attention; D001522:Behavior, Animal; D001717:Birds; D002540:Cerebral Cortex / Q000502:physiology; D004777:Environment; D005106:Exploratory Behavior; D006185:Habituation, Psychophysiologic; D008322:Mammals; D008636:Mesencephalon / Q000502:physiology; D012890:Sleep; D012919:Social Behavior; D013045:Species Specificity; D014851:Wakefulness