Body Weights of Adult and Juvenile Northern Pocket Gophers, Thomomys talpoides, in Central Alberta Alfalfa Fields

Abstract

In an effort to recognize adults from juveniles in late summer and early fall, carcasses of Northern Pocket Gophers (Thomomys talpoides) captured from April to October 1994 in a pure alfalfa (Medicago spp.) field in Camrose and a mixed alfalfa-orchard grass (Dactylis glomerata)-dandelion (Taraxacum spp.) field in Lacombe, in central Alberta were analyzed. Mean weights of adult males and females were significantly (P < 0.05) larger than those of juveniles with near-adult body sizes in late summer and early fall. On the basis of the limits of 95% confidence intervals for individual values in Camrose and Lacombe, live-captured males weighing < 130 g could be classified as juveniles; those that are > 180 g would be adults. Males weighing between 130 and 180 g could be either juveniles or adults. Live-captured females weighing < 110 g would likely be juveniles. With larger animals, the pubic symphysis should be used to distinguish young females from adults. Given the variability of body weight in Northern Pocket Gophers, it is suggested that criteria for aging based on weight be derived for local populations in specific habitat types. On average, Northern Pocket Gopher males and females from Camrose were significantly (P < 0.05) heavier than those of Lacombe. Animals from both fields were, on average, heavier than those previously studied in natural-vegetation communities. Differences in the food nutritional quality may explain the observed variation in body weights among populations.