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Abstract

Interference of nonmating individuals in copulations was studied for 14 months in a harem troop of free-ranging Hanuman langurs living in Rajasthan/India. 80.6% of 346 sexual interactions were harassed by members of all age-sex classes except infant-I. A mean of 1.6 (range 1–7) harassers cooperated entailing a mean of 1.9 (range 1–7) successive copulatory attempts of the disturbed couples. Rank did not influence the direction of male-male harassment. However, higher-ranking adult females harassed lower-ranking twice as often (67.2%) as vice versa (32.8%). Moreover, only 58.8% of copulations of the 3 top-ranking females were disturbed against 96.4% in the 3 lowest-ranking.

Harassment by adult males seems to reflect intrasexual competition for insemination of females. Harassing females possibly try to limit births and reduce future resource competition. Since insemination of one female may reduce the probability of another female's impregnation, harassment might also express sperm competition. The latter hypothesis is supported by the fact that 75.0% of all copulatory attempts of pregnant females were likewise disturbed. Since interference in nonfertile matings cannot reflect resource competition, it is assumed that copulating pregnant females try to deplete the sperm available to competing fertile females. Immatures harassing maternal copulations obviously try to delay the births of siblings who are rivals for nurture.