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Sciurus nigereastern fox squirrel

By Bridget Fahey

Geographic Range

Fox squirrels are found throughout the eastern and central United States, south into northern Mexico, and north into Canada. They have been introduced into urban areas in western North America as well.

Habitat

Fox squirrels, like other tree squirrels, use trees for escaping from predators. They are fast and agile in the trees. They can readily escape predators on the ground and large birds of prey if they can seek refuge in the trees.

Fox squirrels are found in a diverse array of deciduous and mixed forest. Areas with a good variety of tree species are preferred due to variability in mast production.

Physical Description

Fox squirrels are a medium-sized tree squirrel with no sexual dimorphism. The dorsal pelage is buff to orange and the venter is rufous. Some varieties in the southeastern United States are black. These squirrels have 8 mammae. Tail is well furred. Ear tufts often develop in winter.

Adaptations for climbing include sharp recurved claws, well developed extensors of digits and flexors of forearms, and abdominal musculature.

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    696.0 to 1233.0 g
    24.53 to 43.45 oz
  • Average mass
    800.0 g
    28.19 oz
  • Range length
    454.0 to 698.0 mm
    17.87 to 27.48 in
  • Average length
    595.0 mm
    23.43 in

Reproduction

Females can mate with several males, but the males will compete with each other to determine who gets to mate first.

Fox squirrels can mate any time of year; this behavior peaks in December and June. Males follow females prior to estrus, smelling the perineal region. Males aggregate in the home range of a female when she begins estrus. Dominance hierarchies form among the males to determine mating privilege. Copulation lasts less than thirty seconds, and females can mate with several males. A copulatory plug forms after mating. Gestation lasts 44-45 days. Average litter size is 2-3, but litters range between 1 and 7. Young are born naked, weighing between 13-18 g. Eyes open at week 5, and young are weaned at week 8. Sexual maturity is attained at 8 months for females, 10-11 months for males. Females can produce 2 litters in a year, although 1 is the norm.

  • Breeding season
    Breeding occurs from December to February and May to June.
  • Range number of offspring
    1.0 to 6.0
  • Average number of offspring
    3.0
  • Average number of offspring
    3
    AnAge
  • Average gestation period
    44.0 days
  • Average gestation period
    44 days
    AnAge
  • Average time to independence
    3 months
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    353 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    1 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    353 days
    AnAge

Female fox squirrels care for their young in the nest for 6 weeks. When the mother leaves her young in the nest she covers them with nesting material. Young fox squirrels disperse away from their mothers range in the fall of their first year. Male fox squirrels disperse farther and may die more as a result.

Lifespan/Longevity

Fox squirrels have been known to live to 18 years old in captivity. Under natural conditions the average lifespan is 8 to 18 years old, though most squirrels die before they reach adulthood.

  • Range lifespan
    Status: captivity
    18.0 (high) years
  • Average lifespan
    Status: wild
    7.0 months

Behavior

Primarily arboreal and diurnal. Generally, fox squirrels are not gregarious, although they come together during the breeding season when females are in estrus. Males have larger home ranges than females. Squirrels threaten one another by an upright stance with their tail over their back, followed by a quick flick of the tail. Scent-marking is another form of intra-specific communication used by fox squirrels. Vocalizations in the form of barks and chatters, distress screams, and high-pitched whines during mating are common. Fox squirrels are serially polygynous. Mating chases involve one female and a number of males, with the successful male guarding the female to prevent others from mating with her; males do not help in the raising of young.

Communication and Perception

Fox squirrels have excellent vision, even in dim light. They have well-developed senses of hearing and smell. Scent marking is used to communicate among fox squirrels. They use a variety of sounds to communicate, including barks, chatters, distress screams, and high-pitched whines during mating. Fox squirrels will threaten one another by standing upright with their tail over their back and flicking it. Fox squirrels also have several sets of vibrissae, thick hairs or whiskers that are used as touch receptors to sense the environment. These are found above and below their eyes, on their chin and nose, and on each forearm.

Food Habits

A wide variety of foods are taken, ranging from vegetative matter to gall insects, moths, beetles, bird, eggs, and dead fish. Acorn, hickory, walnut, mulberry, and hawthorne seeds are preferred. Food can often become limiting in the winter, so squirrels commonly cache seeds in a scattered fashion for the colder months. Nuts are opened by a levering technique of the lowering incisors, a skill at which squirrels become proficient quickly.

  • Animal Foods
  • birds
  • mammals
  • eggs
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit
  • Other Foods
  • fungus

Predation

Fox squirrels are preyed on mainly by large hawks and owls. Young squirrels may also be taken by snakes. Fox squirrels take advantage of their agility and maneuverability in the trees to escape most predators. They emit alarm calls that alert other squirrels when they see a predator.

Ecosystem Roles

Because squirrels prey so heavily on the seeds of trees they play a significant role in shaping the composition of forests. They may eat (along with other seed-eating animals) almost all of the tree seeds that trees produce in some years. When squirrels bury seeds and forget them, these seeds are likely to sprout where they were placed. Squirrels, therefore, act to promote the growth of certain kinds of trees. Fox squirrels are also important prey items for small predators because of their abundance in the environment.

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Squirrels are be hunted as a food source and for their fur, although the fur is not very valuable. In addition, fox squirrels are important agents of seed dispersal and can aid in succession by burying forest nuts. May play some role in the dispersal of mycorrhizal fungi.

  • Positive Impacts
  • body parts are source of valuable material

Economic Importance for Humans: Negative

Squirrels are often considered a nuisance species due to their raiding of bird feeders and gardens. They are also responsible for some damage to corn crops. They often use electrical lines as routes of travel, and this can cause power outages.

  • Negative Impacts
  • crop pest

Conservation Status

Many subspecies of fox squirrels are endangered due to overhunting and destruction of mature forests.

Contributors

Bridget Fahey (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

Koprowski, J. L. Sciurus niger. Mammalian species No. 479: 1-9.

Nowak, R.M. Walker's Mammals of the World, 5th Edition. Johns Hopkins University Press.

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