Musth is a postpubertal phenomenon. In an Asian elephant population in southern India, bulls have been observed to come into musth from about age 15 years. In younger bulls (15-25 years), however, the intensity of musth as seen from temporal gland activity is low, and the duration is relatively short, lasting from only a few days to weeks. Older bulls show the characteristic, fullblown musth. Younger bulls may show only the early stage of musth seen in older bulls and not enter into the later, intense phase.
At Amboseli, bulls younger than 24 years were never observed by Joyce Poole to show any signs of musth. The average age of onset of musth was 29 years. However, only about 50% of bulls aged 25-35 years were observed coming into musth, while practically all bulls above 35 years exhibited musth. The duration of musth varied from just 1 day to a maximum of about 4
months. There was also a clear relationship between age and duration of musth that lasted for longer periods in larger, and thus older, bulls, which also achieved higher reproductive success (fig. 3.5).
Musth should not be thought of as a phenomenon that is suddenly switched on in male elephants at a particular age. After attaining sexual maturity, there is a gradual build up in the frequency, duration, and intensity of musth in an individual bull, depending on several factors, of which body condition may be the most important. While an individual male generally comes into musth at the same time each year (over a short timescale), different males in a population show wide variation in the time of the year they come into musth. At Amboseli, the highest occurrences of musth were between the months of January and July, during and just after two rainy seasons, when the numbers of females in estrus also peaked. The larger and more dominant bulls came into musth at the most favorable periods, the rainy seasons when the frequency of estrous cows was also higher. At any given time in the year, however, there was at least one bull in musth.
In South Africa's Kruger National Park, Anthony Hall-Martin recorded a clear wet season peak in the number of bulls (>20 years old) coming into musth during 1982-1986, although some bulls were in musth during other months (fig. 3.6). This seasonality in musth also coincided with the peak in conceptions by the cows in the region, suggesting that musth bulls did most of the breeding. By contrast, in Addo National Park, where rainfall is more evenly spread over the year, there was no evidence for any seasonality of musth in bulls or of conceptions by cows. In southern India, Ajay Desai has also observed that more bulls came into musth during the wet season. My observations indicate that the younger bulls generally exhibit musth during the dry season ( January-May), while older, presumably higher-ranking, bulls come into musth during the wet season (June-December). Curiously, Toke Gale's detailed records of the Burmese timber elephants show that most bulls come into musth during the dry months, especially in April-May, just prior to the onset of the monsoon. This does not seem related to any seasonal differences in workload that could potentially influence musth, but could be due to the age profile of the observed bulls.
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