In order to be reproductively successful, male Richardson's ground squirrels must be above ground and producing viable sperm by the time the first female emerges from hibernation and is ready to mate. Because testes regress and return to an abdominal position at the end of each mating season, males must regrow their testes and have them descend back into the scrotum before each subsequent mating season. This regrowth can occur while males are still sequestered in the hibernaculum provided they spend a period of a week or so at the normal mammalian body temperature of 37°C.
Following their final arousal from torpor, male ground squirrels remain underground in a state of euthermy for an average of 7-9 days feeding on food caches. (see Hibernation) Most males commence testicular development during this period, but only those males that have a food cache in the hibernaculum can spend time warm for testicular regrowth. Males without food caches must come above ground within 3-4 days of termination of the last torpor bout. Spermatogenesis is complete either when males emerge from hibernation or several days after emergence. Testes are at their maximum size prior to and during the peak mating period, but begin to regress before the mating season terminates. data
Male ground squirrels lose weight throughout the mating season (see Reproductive Behaviour and Annual Weight Cycle) so the amount of fat at the beginning of the reproductive season may be an important determinant of mating success. In contrast, female ground squirrels gain weight from emergence until parturition (see Annual Weight Cycle), and their mating success is not size dependent.
Within four days after emergence female ground squirrels exhibit a swollen, bright pink vulva indicative of estrus. Females generally enter estrus four days after emergence, and behavioural estrus lasts for several hours on one afternoon. They have only one litter per year. In contrast, the mating season for males lasts for 3-5 weeks, from when the first female in the population comes into estrus until the last female mates.
After insemination, some female ground squirrels have copulatory plugs firmly adhered to their vaginal wall. Formed of coagulated ejaculate within one hour of insemination, copulatory plugs are creamy white and rubbery to the touch. They dislodge within 15-17 hours of being formed. image The function of copulatory plugs is not known. They do not prevent subsequent inseminations because females often mate with more than one male during their several-hour estrous period. The coagulated material is virtually sperm free, so plugs do not serve as a sperm reserve. Possibly plugs push the semen through the cervix and so aid movement of sperm toward the ova.
The emergence of female Richardson's ground squirrels from hibernation is timed such that 6-8 weeks after emergence, when they are at maximum lactation, food is plentiful. Thus, by emerging from hibernation in March in southern Alberta, females have access to adequate fresh green vegetation in late April and early May to support milk production. Additionally, their offspring then have several months of summer available in which to grow and fatten before their first hibernation. (see Hibernation)
Male Richardson's ground squirrels
base their emergence from hibernation on female ground squirrel emergence.
Emerging too early has no reproductive benefits, and may be costly in terms
of survival. Emerging too late results in lost mating opportunities,
as many of the females will already have mated. Thus in southern
Alberta, the optimal time for males to emerge is in late February and early
March, about 2 weeks before females emerge from hibernation.
