Sexual Segregation in the Nilgiri Tahr (Hemitragus hylocrius)

Abstract

Studied sexual segregation in the Nilgiri tahr Hemitragus hylocrius from November 1994 through April 1995 at Eravikulam National Park, Kerala, India. This Study covered the post-rut phase of the tahr's annual cycle. The objectives of the study were to examine whether sexual segregation exists in the tahr identify modes of segregation, and compare empirical findings with some theoretical hypotheses advanced to explain sexual segregation. I investigated differences in ,the way the sexes occurred in social units, used space, chose forage and budgeted time. Data on group composition and habitat selection were collected and two trails monitored regularly. Availability of forage was quantified in three habitat strata. Differences in dietary quality were estimated with two faecal indices - crude protein and ash. Data on activity budgets were collected from group scans. Throughout the study period, tahr occurred mostly in female groups, bachelor groups, and 1 to a lesser degree, in mixed groups. They showed marked segregation in the use of habitat types. Male groups used the rolling grasslands at the higher elevations intensively, whereas the female groups were distributed in rocky areas dominated by Plebophylllum kunthianum, and in areas of grass interspersed with cliffs. Male and female groups showed distinct differences in their choice of habitat. Males chose areas of high absolute amounts of graminoid forage, whereas females preferred areas of greater security; these were typically areas high slope angles and percent rockiness. - There were no differences in the levels of crude protein and ash in the pellets of male and female tahr. Differences were also found in the time-activity budgets of the sexes. Although all age sex classes spent equal proportions of time feeding, large males spent a greater proportion of their time resting than either small males or females. Females on the other hand, spent a greater proportion of their time moving than did individuals in the two male classes