Multiple paternity in Belding's ground squirrel litters.

Sexually receptive female Spermophilus beldingi (Rodentia: Sciuridae) usually mate with several different males. The paternity of 27 litters born in 1977 and 1978 was ascertained by combining field observations of mating with laboratory paternity exclusion analyses. Most of the litters (78 percent) were multiply sired, usually by two or three males. This may be the highest frequency of multiple paternity ever directly demonstrated in a natural population.