Nutritional Ecology of the California Vole: Effects of Food Quality on Reproduction

Abstract

California voles primarily eat the green shoots of grasses during the wet, breeding season (winter) and switch to grass seeds during the dry, nonbreeding season (summer). This suggest that nutritional factors control the timing of breeding, but until now there has been no indication of which nutrients are responsible. This paper reports the results of experiments conducted to test the following hypotheses: (1) grass seeds will not support extensive reproduction by California voles, and (2) low calcium and sodium concentrations in grass seeds can account for reduced reproduction on seed diets. In 12—wk feeding trials neither multiparous adults nor nulliparous subadults produced as many pups when fed grass seeds as when fed a laboratory diet (rabbit chow). Subadults fed grass shoots had intermediate success. Concentrations of calcium and sodium, but not protein and phosphorus, were lower in seeds than in rabbit chow, grass shoots, and diets recommended for laboratory rodents. Subadult animals had positive net balances of nitrogen and phosphorus, but not of calcium and sodium, when fed grass seeds. Although subadult females generally produced fewer young than adult females, subadult voles fed grass seeds and supplemental calcium and sodium in their drinking water reproduced as well as adult voles fed rabbit pellets. All these results were consistent with the hypotheses given above and lend credence to previous suggestions that nutrition (particularly mineral nutrition) exerts important influences on the population densities of lemmings and voles.