Red squirrels become sexually mature at about one year of age. The breeding season begins in midwinter, usually in February or March, and continues into summer. Females are in estrus for less than a day and may be pursued by and/or solicit the attentions of several males. This activity often leads to raucous breeding chases involving many squirrels that may last for several hours. Females usually have one, or sometimes two litters per year, typically with 3-5 young per litter. The altricial young are born after a 35 day gestation period and are nursed in the nest for about 45 days before emerging. They may remain with their mother for several weeks or months before moving away to establish their own territories. In some instances the mother may relinquish a portion of her territory to one or more of her offspring, and move to establish a new territory herself. Juvenile mortality is high. In other populations about 50% of the juveniles will die before they reach the age of six months, and another 25 to 30% typically do not survive to the end of their first year. Once they establish a territory the average life expectancy is about three years. Predators include avian species (northern goshawks, sharp-shinned hawks, cooper's hawks, red-tailed hawks, Mexican spotted owls and great-horned owls) and mammalian species (gray fox and bobcats).