Life History Studies of Nutria, or Coypu, in Coastal Louisiana

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Abstract
A wild nutria population, Myocastor coypus, was studied in coastal La. during the period Jan., 1946, to April, 1948. The best coypu range is limited to the fresh-water marshes which lie farther inland and adjoin the brackish coastal marshes extending w. more than 100 mi. from Morgan City to Creole, La. Life histories were studied and the data are reported. The habitat is descr., foods listed and discussed, observations of burrowing and winter platform building are presented and nests are descr. Data on reproduction are presented and discussed under litter size, litter pattern, fecundity and young at birth. Data on growth and sexual development are presented and discussed. Most of the coarse emergent and floating-leaved aquatic plants of the La. fresh-water marshes are used as food. Winter platforms are built during the same period that burrows are used and have the same function as burrows. In La. coypu showed preference for location of winter platforms and nests in sawgrass (Cladium jamaicense) and giant cutgrass (Zizaniop-sis miliacea). The data on reproduction show an inverse linear relationship between mean litter size and rate of embryo absorption. There was a significant increase in absorption of embryos concurrent with reduction in litter size and decreased in available food. Mean size of litters decreased when over utilization of habitat resulted in a marked reduction in the amt. of food available. Additional data on reproduction show that the mean litter size of the 1st litter is smaller than subsequent litters. The size of coypu litters increases with body size and age of the female, but there is a decrease in size of alternate litters, beginning with the 3d litter. The series litter pattern of coypu is fixed and is not greatly altered by a moderate change in diet. However, a severe dietary deficiency may result in distorting and finally destroying the pattern. Max. wts. and measurements of wild coypu were found to be 18 lbs. at 43 in. for males and 17.5 lbs. at 41.5 in. for females. While max. length growth is approx. the same, the avg. max. wt. of wild coypu was only 70% of that of penned animals. No wt. differences occurred between sexes in the wild population. Length growth of coypu is relatively unaffected by food shortage resulting in moderate to semi-severe wt. losses. Relatively greater wt. losses of males, as compared to females, under the same conditions of food shortage, indicates a greater food intake requirement for opt. growth of males. The larger percent of wt. loss and slower increase in wt. of the adolescent segment, under conditions of food shortage, as compared to the sexually mature segment of the population, indicates a relatively greater food requirement by the adolescent segment for normal growth. Starvation losses will occur among sexually immature animals before deaths from starvation occur among sexually mature animals. Puberty was attained at slightly under 4 mos. of age where no food shortage occurred; it was delayed an avg. of 1.3 mos. on food-deficient range. In a wild coypu population, food supply is a major factor affecting reproduction, particularly with respect to variation in fecundity and rate of sexual development.