Fox sparrows tend to be monogamous and solitary while breeding. The male usually sings in the general area of the nest, while keeping himself hidden. The sounds created are identified as call-notes, and they have not been shown to be a way to attract females, but rather are a song as a protest against intrusion into the territory by other males. These typically shy birds only become defensive when their nest territory is invaded by other birds.
Mating System: monogamous
Fox sparrows may breed up to two times a year. The breeding season is from mid-May to July. The number of eggs laid per clutch ranges from 3 to 5. The eggs are pale blue to pale green with thick brown spots. The nests of fox sparrows are typically on the ground or in very low branches. They are typically no more than 7 feet above ground. The nests are made out of twigs, dried grass, stems, and bark. The cup shaped nest is lined with grass, animal hair and feathers. It takes from 12 to 14 days for the eggs to hatch; incubation is done mostly by females. The young are typically tended to and fed by both parents. The young fox sparrows fledge in 9 to 10 days after hatching. While there was no specific information on time to independence for this species, the time to independence for sparrows in general is about 10 days. On average, both sexes of fox sparrows reach reproductive maturity when they are about 1 year old.
Breeding interval: Fox Sparrows may breed up to two times a year.
Breeding season: Fox Sparrows breed from mid-May to July
Range eggs per season: 3 to 5.
Range time to hatching: 12 to 14 days.
Range fledging age: 9 to 10 days.
Average time to independence: 10 days.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization
Average birth mass: 2.7 g.
Average eggs per season: 4.
Fox sparrows are altricial. The eggs hatch after about 12 to 14 days (females do most of the incubation), and the young fledge about 9 to 10 days later. Fox sparrows are tended to by both parents. They provide food (mainly insects) and protection. While there was no specific information on time to independence for this species, the time to independence for sparrows in general is about 10 days. Both parents will use the broken-wing display to protect their young from predators.
Parental Investment: no parental involvement; altricial ; pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)