The physical and behavioral postnatal development of woodchucks (Marmota monax) was analyzed from birth to 42 days of age, the age at which weaning begins. Postnatal growth was evaluated by means of daily measurements of body weight, body length, tail length, and length of hind foot. Data on length of ear pinnae, vibrissae, and fur, and on the timing of appearance of some events of physical development are also presented. We considered postnatal development of locomotion, alertness, exploratory behavior, feeding, and comfort and social behavior. Our results indicate no sexual dimorphism in body size in young woodchucks, despite its occurrence in adults. Intraspecific comparisons reveal that woodchucks from different populations show marked variation in growth rate. The high level of intraspecific variation in developmental rates of sciurid rodents provides a warning to those performing interspecific comparisons. The data also suggest that the ratio of growth rate to adult body weight is not related to environmental severity. Behavioral development in M. monax is similar to that of ground squirrels but faster than that of tree squirrels and flying squirrels. There is also no direct relationship between size and timing of behavioral development in sciurid rodents. The behavioral repertoire of young woodchucks is simpler than that of young Spermophilus lateralis, another asocial species. It is possible that specific differences in rates of development of social interactions led to such differentiation in the repertoire of social behavior.
Biological mechanisms discriminating growth rate and adult body weight phenotypes in two Chinese indigenous chicken breeds
