R. H. Chabreck

Fetal counts of muskrats (Ondatra zibethicus) yielded an average of 2.97 ± 1.06 fetuses per litter (range: 1 to 5). Placental scars averaged 7.97 ± 4.34 per breeding female (range: 1 to 22) and indicated production of 2.7 litters per breeding female per year. Corpora lutea counts disclosed that litter sizes ranged from I to 7, averaged 3.54 ± 1. 15, and differed significantly from fetal counts. Litter size as determined by lodge surveys (i = 2.18 ± 0.25) was less than that determined by fetal counts and represented post-partum mortality. Mortality estimates indicated a loss of 16.1%...

Muskrat (Ondatra zibethicus rivalicius) movement and activity patterns were studied in a Louisiana coastal marsh. Trap success was 8.2% in January-February, but only 3.3% in June-August. Of 46 muskrats captured, 65.2% were males. Lodge use was greater than expected in JanuaryMarch and less than expected in April, July and August (X2 =92.5, N =557, P < 0.01). No radio-collared muskrats (11 males and 6 females) were observed rearing young. Five (33.3%) muskrats emigrated in the spring and 3 of the dispersals occurred during a storm tide (29 March- 3 April). Long movements (>70 m)...