The abnormal conduct of capercaillies Tetrao urogallus.

The frequency, behavior, and testosterone levels of deviant capercaillies were studied in southern Finland. Roughly 1% of the population was estimated to behave abnormally. Deviant males display and show threatening behavior toward not only humans, but also attacked stuffed capercaillie males and without hesitation copulated with a stuffed female. Deviant females appear tame and crouch in front of humans, but avoid males. The testosterone level in deviant males was about five times higher than that of normal displaying males. The origin of this striking phenomenon is still unclear, although it must be connected with display. Two, though not mutually exclusive, proximate mechanisms for the development of this abnormal behavior are presented: anomalous sex hormone concentrations and incorrect sexual imprinting. The ultimate reason for the apparent increase in numbers of deviant capercaillies is probably logging which diminishes populations and, thereby, favors the spreading of abnormal behavior.