Reproductive Characteristics of the Male Grizzly Bear in the Continental United States

January 1, 1998

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We evaluated testicular growth, seminiferous tubule development, and age of sexual maturity in 20 male grizzly bears (Ursus arctos horribilis) killed in Montana and Wyoming between 1978 and 1992. Seminiferous tubule diameter did not differ among the regions of each testicle sampled. Testicular mass was related linearly to age. Seminiferous tubule diameter was related non-linearly to age. Mean testicular mass, volume, and seminiferous tubule diameter were smaller in immature bears than in mature bears. Based upon the presence or absence of spermatozoa in the lumen of the seminiferous tubules, sexual maturity in grizzly bears from the continental United States is attained at approximately 5.5 years of age.

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