Methods of Determining Litter Size in Beaver

Estimates of litter size in beaver (Castor canadensis), based on counts of corpora lutea, placental scars, and corpora albicantia, were compared to known litter size determined by fetus counts. Estimates based on corpora albicantia (x = 4.2) were significantly higher (P < 0.05) than with any other method. Numbers of corpora lutea (x = 3.0), placental scars (x = 2.8), and fetuses (x = 2.6) did not differ (P > 0.05). No reproductive parameter differed by beaver age-class.