Based on 65 free-ranging gray wolves (Canis lupus) of known age and 25 of estimated age examined during summers of 1970-2004 in northeastern Minnesota, body mass of both males and females peaked at 5 or 6 years of age, with mean masses of 40.8 kg and 31.2 kg, respectively. Testis size varied as a function of age and month through at least 8 years of age, with length plus width ranging from 1.9 to 7.8 cm. Most females aged 4-9 years bred based on assessment of nipple sizes; those that had not bred had average lower body mass than those that had. This is the 1st report of such data from known-aged wolves.
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Age-related body mass and reproductive measurements of gray wolves in Minnesota