Age-Related Body Mass and Reproductive Measurements of Gray Wolves in Minnesota

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. Information about development and mass changes of free-ranging gray wolves (Canis lupus) has been scattered, anecdotal, or piecemeal. Primarily this has been because wolves are long-lived, were scarce and difficult or expensive to live-capture (Mech 1974), and because aging techniques for live wolves had not been developed. Wolf pup growth and development was described for captive (Mech 1970; Pulliainen 1965) and free-ranging (Van Ballenberghe and Mech 1975) animals. Seasonal mass change (Seal and Mech 1983) and nipple measurements (Mech et al. 1993) of wolves with known reproductive histories were documented for captive wolves but were not related to ages. Testis measurements separating yearling wolves from older animals have been published, but no data were presented for various-aged adults (Gese and Mech 1991). Testis size has been said to vary with season, but no data were given (Seal et al. 1987). However, as a result of a study in which free-ranging wolves have been livetrapped, examined, ear-tagged, and radiotagged from 1968 through 2004 (Mech 1979, 2000), enough known-aged pups were so marked and then recaptured as adults of various known ages that data are now available relating wolf measurements to age. In addition, the development of tooth-wear charts from known-aged wolves (Gipson et al. 2000) allowed accurate age estimates of livetrapped wolves, which yielded additional data (Mech, in press). I thus present here information about the body mass and testis and nipple measurements of free-ranging Minnesota wolves of various ages. The study area encompassed some 2,060 km 2 immediately east of Ely in the east-central Superior National Forest (488N, 928W) of northeastern Minnesota. Topography varies from large stretches of swamps to rocky ridges, with elevation ranging from 325 to 700 m above sea level. Winter temperatures below À358C …