Eastern Fox Squirrel (Sciurus niger)

County List:

Rule:

Mixed Forested/Nonforested Landscapes

1st alternative:
      (Oak (Sm Saw or Lg Saw Uneven))
      or (Northern Hardwoods (Sm Saw or Lg Saw or Uneven))
      or (Assorted Hardwoods (Sm Saw or Lg Saw or Uneven))
      or (Mixed Northern Hardwoods (Sm Saw or Lg Saw or Uneven))
      or (Mixed Upland Hardwoods (Sm Saw or Lg Saw or Uneven))
      or (Bottomland Hardwoods (Sm Saw or Lg Saw or Uneven))
   containing:
      (Dead Down Woody Debris and Living Cavity Trees and Mast)
   adjacent to:
      (Any Cropland)

2nd alternative:
      Savanna
      or Residential
   containing:
      (Dead Down Woody Debris and Living Cavity Trees and Mast)

Habitat List:

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Literature:

The fox squirrel prefers deciduous trees in areas that lack a well-developed understory. It frequents open woodlots, forest-field edges, and urban situations. This species avoids the shaded interior of vast forests. Deforestation allowed the fox squirrel to spread into our area at the expense of the gray squirrel, which prefers extensive tracts of mature trees.

This large squirrel prefers hollows in deciduous trees for over-wintering and raising young. A typical nest cavity measures 6 inches across and 15 inches deep, has an opening about 3-5 inches wide, and contains an insulating layer of dry leaves or grass. In the summer, this species often builds a bulky nest of leaves and twigs, high in the branches of an oak, pine, elm, or maple.

In spring and summer, this rodent eats the buds, flowers, and fruits of woody plants such as maple, elm, and willow. Berries, grapes, and cherries also are eaten when in season, and the fox squirrel apparently pilfers corn more often than the gray squirrel. Extra protein comes in the form of an occasional grub, caterpillar, egg, or young bird.

Distribution: Unlike the gray squirrel, the fox squirrel is more at home at the forest edge rather than in the extensive, uncut Michigan woodlands of the earliest pioneer days. Fox squirrels apparently lived in Michigan in pioneer times only in the southwestern part of the state where "oak openings" (northeastern vestiges of the western prairies) provided the needed habitat.

Logging and farming in Lower Peninsula Michigan produced habitat highly suitable for fox squirrels. This resulted in a steady encroachment by fox squirrels into the areas occupied by the declining gray squirrels, who strictly preferred the mature nut-bearing timber lands.

Habitat Preferences: From the oak openings of southwestern Michigan, fox squirrels fanned out through the mosaic second-growth shrub and forest lands of Lower Peninsula. The "edge effect" produced by agricultural practices and lumbering provided thee pathways. The fox squirrel's adaptability to shrubby fencerows allowed the species to travel easily between the island-like woodlots now dotting much of the lower Michigan landscape. However, wooded areas of less than five acres may not provide all the basic needs for year-around squirrel survival. Allen noted that grazing of such woodlots by domestic livestock is less harmful to fox squirrels than to other game species.

Durward Allen looked at four major habitats in southern Michigan, and concluded that mature oak-hickory woodlands are the best habitats for fox squirrels. Beech-maple woodlands rank second in providing environmental essentials. In forested stands where beech and maple are well mixed with oaks, ash, elm, basswood, ironwood and other species, the quality is noticeably improved and rivals oak-hickory as a favored fox squirrel habitat. However, when the Michigan forest succession changes from an oak-hickory stage to a beech-basswood-maple stage the fox squirrel tends to decline and the gray squirrel increases. Scrub oak on sandy soils of southwestern Michigan ranks third as fox squirrel environment in Michigan. The fourth and least productive of the major fox squirrel habitats is streamside woodlands. Where the tree species composition is mostly elm and maple, the forest stand may be little used. Where the mix includes ash, elm, red maple, butternut, swamp white oak, sycamore, and such bordering species as basswood, red oak, beech, and walnut, the habitat may be as productive for fox squirrels as some of the better upland woodlands. As Allen noted, forested areas bordering streamways represent the most continuous forest growth in southern Michigan. This habitat is also enhanced as fox squirrel habitat because it often borders farms where a diversity of land manipulations add to the squirrels year-around food supply.

Behavior: Fox squirrels probably spend more time on the ground (foraging or moving between trees) than do gray squirrels. Part of this ground movement is along brushy or tree-lined fencerows and across open areas where gray squirrels rarely venture.

The fox squirrel will den in tree hollows and also construct leaf-twig nests. Studies by Nixon et al. in Illinois suggest that a fox squirrel may need as many as one to two cavities per acre. Preferably the entrance should be no more than 5 inches wide, with cavity at least 14 inches deep. The best holes result from a mature tree's self-pruning process and a combination of central rotting (plus pecking by woodpeckers and gnawing by squirrels) of both the broken branch and surrounding growth of the tree's cambium layer. Unfortunately, such trees are frequently old and may fall or be culled in the course of woodlot management. To make a good squirrel den, a tree cavity must be positioned so that water cannot collect in the hole; it must also be small enough to exclude raccoons or other large tree hole users. Allen found good tree-hole dens for Michigan fox squirrels in mature white oak, soft maple, elm, sycamore, and beech. Of these, he noted white oak and beech produced the best cavities in the uplands and elm and red maple in the lowlands.

In the absence of suitable tree holes, especially in many of Michigan's managed farm woodlots, fox squirrels rely on leaf nests; a combination of leaf nests and cavities provides the best year-around quarters. Although some leaf nests may be no more than 10 ft off the ground, most are higher, with grape vines offering favored attachment sites. In a study in Allegan County, Allen found the average leaf nest was 30 feet above ground in a tree 7 inches in dbh. In a study of 120 leaf nests, 55 were in black oak, 42 in white pine, 11 in red maple, 9 in beech, and 3 in white oak. It was Allen's opinion that the fox squirrel picks the larger trees for nest building with white pine and black oak often favored.

Associates: In general, the fox squirrel favors the mixed southern hardwoods and conifers interspersed with numerous openings and second growth shrubs and trees. The gray squirrel prefers the extensive stands of mature upland or lowland southern or northern hardwoods, shying away from openings and glades. The red squirrel seems more at home in coniferous or mixed coniferous and hardwood forests than in hardwood (deciduous) stands unless they are in moist lowlands. In Michigan, these species compete for tree holes and artificial den boxes.

Food Habits: Fox squirrels eat plant and animal foods. In late April and early May, Michigan fox squirrels respond energetically to emerging tree and shrub growth at a time when winter stores and foods salvaged from under snowdrifts and leaf litter are depleted. Following autumns of low acorn and nut production, food supplies in late winter and early spring can be critically sparse for squirrel populations, especially for females in late pregnancy or with nursing litters. Foods in late March, April and May include flower buds and samaras of silver and red maple, buds and flowers of sugar maple and burr oak, pistillate catkins of willow, staminate catkins of cottonwoods, flowers of hackberry, elm and beech, and buds of elm and basswood. During this period, fox squirrels also probe in forest litter for adult beetles and other insects and for tubers, bulbs and roots; nests of robins, blue jays, and other birds are robbed. Summer foods include strawberries, serviceberries, haws, plums, raspberries, blackberries, greenbrier, blueberries, grapes, chokeberries, cherries, basswood, box elder, black ash, hard maples, dogwood, elderberries and others. Beetles, grasshoppers, grubs and other larval stages of insects, bird eggs, nestling birds, green corn and other agricultural crops are also fair game for fox squirrels. The appearance of acorns, nuts and other ripening seeds in autumn allows the fox squirrel to "fatten-up" for winter and to gather these nonperishable foods for storage.

Ecology: Although found in a diversity of deciduous and mixed-forest habitats, fox squirrels are common in forest patches <40 ha with an open understory. Low understory stem densities are an important component in some localities but not in others. Densities of Sciurus niger are highest in habitats composed of trees that produce winter-storable food such as oaks, hickories, walnuts, and pines. Due to annual variability in mast production, a diversity of tree species is important to support high densities of fox squirrels.

Formation of den cavities requires 8-30 years depending on wood type. Addition of artificial nest boxes did not increase densities or survival except for adult males. However, 1-2 boxes/2.5 ha may be beneficial. Girdling or otherwise deadening of hardwoods and prescribed burning are detrimental to squirrels. Selective cutting of trees ³30.5 cm without removal of culled trees has little effect on population parameters except for temporarily low recover rates of females after >40% of the merchantable volume was removed. Winter feeding with corn did not increase survival or densities.

Entrance openings to nest cavities average 7.4 by 9.4 cm in size.

Eastern gray squirrels and fox squirrels can by syntopic. Food preferences are similar. Sciurus niger females displace S. carolinensis from concentrated food sources in the breeding seasons, but eastern gray squirrel females are more efficient at finding food. Removal of adult female fox squirrels led to slight shifts in space use of female eastern gray squirrels. Eastern gray squirrels replaced fox squirrels in a suburban neighborhood as food trees matured. Eastern gray squirrels inhabit areas with dense understory. Woodlot size may be important; larger woodlots tend to have higher densities of understory and eastern gray squirrels.