Squirrels
Info
Nests are most commonly constructed of grass in the branches of spruce trees. Nests are also excavated from witches' broom - abnormally dense vegetative growth resulting from a rust disease - or cavities in the trunks of spruce or poplar trees. Each individual red squirrel has several nests within its territory and females with young move offspring between nests. Red squirrels experience severe early mortality (on average only 22% survive to one year of age). The survival probability, however, increases to age three at which point it begins to decrease again. Females that survive to one year of age have a life expectancy of 2.3 years and a maximum lifespan of eight years.
Reproduction
Ovulation is spontaneous with red squirrels. Females enter estrus for only one day, but venture from their territory prior to ovulation and these exploratory forays may serve to advertise their upcoming estrus. On the day of estrus, females are chased by several males in an extended mating chase. Males compete with one another for the opportunity to mate with the estrous female. Estrous females will mate with 4 - 16 males. Gestation time has been reported to range from 31 to 35 days. Females can breed for the first time at one year of age but some females delay breeding until two years of age or older. Most females produce only one litter, but in some years reproduction is skipped while in other years some females attempted to breed twice. Litter sizes typically range from 1 to 5, but most litters contain 3 or 4 offspring. Offspring are pink and hairless at birth and weigh approximately 109. Offspring grow at approximately 1.8 g/ day while nursing but do not reach adult body size until 125 days of age. Offspring first emerge from their natal nest at around 42 days of age but continue to nurse until approximately 70 days of age.
