Once females begin to emerge from hibernation, males defend areas that change on a daily basis as each male attempts to maximize his proximity to females that are in estrus on that day. Males compete fiercely with each other for access to estrous females.
Female Richardson's ground squirrels enter estrus shortly after emergence from hibernation, and they usually mate on their third or fourth day out of hibernation. Each female's estrous period only lasts about 2-3 hours. During this time the female mates with 1 to 4 males. Copulation usually occurs underground.
Once they are impregnated, female Richardson's ground squirrels become intolerant of all males, including any males with whom they have mated. If a female Richardson's ground squirrel loses her litter during pregnancy or lactation, she is incapable of breeding again until the following year. Only one litter can be produced a year.
The testes begin to regress during the mating season, and by the time the last female to emerge from hibernation has mated all males have small testes. The testes cease producing sperm and then return into the abdominal cavity until the following spring.