The Testosterone Takeover
In the scrublands of Ruhuna National Park, a complex social calendar governs the reproductive lives of male Asian elephants (Elephas maximus). This schedule revolves around musth, an annual physiological event marked by a massive surge in testosterone. Levels of this hormone can increase by an average of 60 times, and in some individuals, up to 140 times their normal baseline. This hormonal flood triggers dramatic physical and behavioral changes.
The most visible signs are secretions from the temporal glands, located between the eye and ear, and continuous urine dribbling. The thick, tar-like temporal gland secretion, called temporin, contains a cocktail of phenols, cresols, and aromatic compounds like farnesol. This, combined with chemicals in the urine, creates a powerful scent that signals the male's condition to all other elephants in the area. During musth, males will often rub their heads on trees to leave behind these chemical messages. They may also produce a low-frequency "musth rumble" that can travel for miles, advertising their state to receptive females and warning off rival males.
A Socially Timed Transformation
Long-term behavioral studies on the elephants of Ruhuna, now part of the Yala Protected Area Complex, have overturned earlier assumptions about musth. It is not a randomly or seasonally timed event. Instead, its timing and duration are linked to a bull's age and his position in the social hierarchy.
Older, more dominant bulls, typically over 30 years of age, experience longer and more pronounced musth periods. They strategically enter this state to coincide with the peak number of receptive females. This gives them a distinct reproductive advantage. Younger males, between 15 and 30 years old, have shorter, less intense musth cycles. Often, their musth is timed to occur outside of the main breeding windows used by dominant bulls. This appears to be a strategy to avoid direct, and potentially fatal, conflict with larger, more experienced rivals. In some cases, the presence of a high-ranking musth bull can even suppress the onset of musth in lower-ranking males in the vicinity.
This social modulation of a physiological state shows an interaction between hormones, behavior, and social structure. A male in musth spends less time feeding and more time roving, sometimes expanding his home range significantly to seek out females. The ability to enter this energetically demanding state is itself a signal of fitness, and females preferentially select males in full musth.