BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Tamiasciurus hudsonicus | Red Squirrel 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Diurnal Activity:  Red squirrels are diurnal and active year-round.  Peak
activity occurs 2 hours after sunrise and just before sunset, but
red squirrels are active most of the daylight hours [25].

Movement:  Rusch and Reeder [34] reported that red squirrels move from
quaking aspen and pine stands to spruce stands in the spring.  Fall
movements are largely those of juveniles moving away from denser
populations of adults in spruce stands.

Breeding Season:  Red squirrel breeding season varies with latitude and
elevation.  Generally, the breeding season peaks from March to August,
but breeding may begin as early as January and continue as late as
October.  Mating is promiscuous [13,25].

Nesting and Litter Size:  Female red squirrels prefer to nest in natural
tree cavities or abandoned woodpecker (Picidae) holes.  If none are
available they build a leaf [25] or grass nest [27] in the crotch of a
limb high on a densely foliated tree, or use a fallen tree, rock pile,
underground burrow, or man-made structure.  There are usually four or
five young per litter (range: one to eight).  Generally there is only
one litter per year, but occasionally a female bears two litters in one
year [25].

Development of Young:  Red squirrel young are born naked and blind.  By
6 days there is noticeable fur growth and by 20 days there is a good
covering of dorsal fur.  Their eyes open at 27 to 35 days.  They are
mostly furred by about 8 weeks.  The young red squirrels begin making
limited excursions from the nest at 6 to 7 weeks, and forage at a
greater distance by about 10 weeks [25].  Weaning occurs at about 7 to 8
weeks in New York [25] and about 10 weeks in Alberta [24].  Dispersal
usually begins at about 12 to 14 weeks [25].  Female red squirrels in
Canada usually do not breed until their second year.  Males develop
scrotal testes their first spring but it is not known whether they breed
at that time [24].

Dispersal of Juveniles:  Juvenile red squirrels disperse in the fall in
search of suitable territory [21].  In Alberta initial movements are
circular; unsuccessful juveniles usually return to the natal territory
until they are successful or are killed.  Occasionally juveniles will
appropriate the mother's territory [24].  Survival of juveniles depends
on establishment of a territory with a food supply adequate for the
entire winter [22].  Juveniles surviving their first winter tended to be
relatively far away from the natal territory.  They appeared to have
acquired larger territories than juveniles that died, with middens that
were constructed by previous owners [24].

Red squirrels tend to disperse and establish territories in relation to
major resources (mature cone-bearing trees) [22].  In south-central
British Columbia relocation of resident adult squirrels a substantial
distance from the study site allowed researchers to monitor red squirrel
recruitment rates.  In the fall red squirrel population density
recovered to control levels on four out of six sites; immigrants were
mostly juveniles.  In the spring, breeding red squirrel population
density recovered to control levels on five out of the six sites; these
sites were also colonized by juveniles in the fall [21].

Mortality and Longevity:  In Alberta average annual mortality was 67
percent for juveniles, 34 percent for adult yearlings, and 61 percent
for older adults [19].  Larsen and Boutin [24] reported annual adult
survivorship for red squirrels in Alberta as 67 to 71 percent.  Captive
red squirrels have lived at least 9 years and wild red squirrels have
lived at least 10 years [25].


PREFERRED HABITAT : 
Red squirrels require mature coniferous trees as a source of cones and
seed [6].  The best cone production occurs in 200- to 300-year old
Douglas-fir, 40- to 300-year old white fir, and 150- to 200-year-old
Engelmann spruce.  The best seed-producing stands of blue spruce (Picea
pungens) are 50 to 150 years old [31].  In central Colorado red
squirrels were present in closed stands of mature conifers [36].  In
west-central Colorado red squirrel caches were more abundant in
conifer-dominated stands than in mixed stands or in stands dominated by
quaking aspen [35].  In Ontario red squirrel tracks were more abundant
in uncut forest than in regenerating stands of various ages with brushy
understories [44].

In two study sites in central British Columbia red squirrels were twice
and over five times as abundant in unthinned stands of 20-year-old
lodgepole pine than in thinned stands.  They were most abundant in
mature stands.  It was suggested that the 20-year-old stands represented
marginal habitat that served as a sink area for excess juvenile red
squirrels [41].

Home Range:  Red squirrel home range size varies with sex, age, and
habitat quality.  Older red squirrels and females tend to have larger
home ranges.  In lodgepole pine forests home ranges varied in size from
0.7 to 2.0 acres (0.3-0.8 ha); in mixed hardwood-conifer stands home
ranges varied from 6.5 to 11 acres (2.6-4.5 ha) [31].  Home ranges of
adult males in New York averaged 6.03 acres (2.4 ha) and ranged from
0.47 to 10.76 acres (0.2-4.3 ha) [25].  Davis [5] reported home ranges
of 3.2 acres (1.3 ha) for males and 3.7 acres (1.5 ha) for females.
Obbard [53] summarized other data on red squirrel home ranges.

Territoriality and Population Density:  Red squirrels actively defend a
territory [18].  Gurnell [15] estimated that defended territories were
60 to 100 percent of the home range in lodgepole pine forests.  In
British Columbia spruce-fir and hemlock-cedar (Thuja spp.) forests adult
territories averaged 2.2 acres (0.9 ha) at low elevations and 1.3 acres
(0.5 ha) at high elevations [52].  There are two types of defended
areas:  most if not all red squirrels in Alberta defend a winter food
cache, which is usually abandoned during the summer, and some red
squirrels defend a "prime" territory which has an adequate food supply
year-round.  One-quarter to one-third of adults defend a prime territory
[19].  In New Brunswick, where red squirrels are scatterhoarders instead
of larderhoarders, territories encompassing the entire food supply are
defended from conspecifics [7].  Smith [52] reported that defended red
squirrel territories in coniferous forests ranged from 0.5 to 3 acres
(0.2-1.2 ha).

Davis [5] reported red squirrel population density of 4 squirrels per 25
acres in mixed jack pine-black spruce stands and 23 red squirrels per 25
acres in white spruce forest.  In southwestern Yukon Territory red
squirrel population densities of 27 per 25 acres (10 ha) and 17 per 25
acres were observed in white spruce forest interspersed with willow
(Salix spp.)-dominated meadows [29].

Many studies, reviewed by Klenner and Krebs [22], indicated that red
squirrel population density varies with cone crops.  Zasada and others
[51] also suggested a relationship between red squirrel density and the
periodicity of white spruce cone production in Alaska since red
squirrels are dependent on white spruce cones for the majority of their
food.  Rusch and Reeder [34] reported that summer populations fluctuated
between 67 and 151 red squirrels per 2,500 acres in mixed habitats.
Sullivan [40] reported that red squirrel population density in British
Columbia increased with food supplementation indicating that food
availability was limiting population density.  In south-central British
Columbia food supplementation (feeders that were kept full of sunflower
[Helianthus spp.] seeds) in Douglas-fir and in white spruce forests
resulted in increases in red squirrel population densities.  The amount
of change was greatest in the population occupying the Douglas-fir
stands, a low density population.  Recruitment rates were very high
initially, but decreased with increasing population density.  Each
population increased to approximately the same density, suggesting that
the factor regulating the maximum population density is not food supply
but territoriality.  When feeders were removed, population density
declined to control levels in about 6 months [22].


COVER REQUIREMENTS : 
Nesting:  Red squirrels prefer natural cavities or abandoned woodpecker
holes for nesting.  When these are not available a leaf or grass nest is
constructed near the top of a tree with dense foliage.  Occasionally red
squirrels use abandoned burrows of other species [6].  Nest trees in
Arizona have crowns that interlock with two or more adjacent trees, and
average 14 inches (35.6 cm) d.b.h. [47].  In New York leaf nests are
built in deciduous trees and pines.  Trees used for leaf nests ranged
from 4 to 16 inches (10.2-40.6 cm) in diameter, were 15 to 70 feet
(4.5-21.3 m) tall, and the nests were 12 to 60 feet (3.7-18.3 m) above
the ground.  Cavity trees ranged from 12 to 36 inches (30.5-91.4 cm) in
diameter and were 20 to 60 feet (6-18.3 m) tall; entrance holes were 7 to
50 feet (2.1-15 m) above the ground [25].

Shelter:  Nest cavities are sometimes used by one to several red
squirrels in severe weather [25].  In winter red squirrels tunnel in
deep snow to find food and escape severe weather [3,13].

Cone-bearing Trees and Food Cache Sites:  Red squirrels in Arizona
require 9 to 25 large, mature, cone-bearing trees (or a larger number of
smaller cone-bearing trees) per territory [27,47].  Red squirrels use
moist, shaded areas for the central food cache.  These areas are created
by groups of mature trees with some understory vegetation nearby.  Large
trees in a group closely spaced in 0.1 acre (0.04 ha) or less are
favored.  Canopy cover at 90 percent of cache sites is greater than 60
percent.  One or more large snags, fallen logs, or live trees act as
support structures for the cache [47].

In Pennsylvania primary red squirrel feeding sites (not caches) were
associated with burrow entrances, overstory cone-bearing pines, and
other primary feeding sites.  They tended to be away from nest trees [50].


FOOD HABITS : 
Red squirrels consume conifer seeds, nuts, buds, sap, tender leaves,
fruits, flowers, fungi, bird eggs, and small vertebrates [6].  In
captive trials white spruce seed alone sustained red squirrels for at
least 3 weeks.  Red squirrels consumed seeds from an average of 144
cones per day per squirrel, probably more than they could consume in the
wild.  Red squirrels lost weight on black spruce seed alone, and
preferred white spruce over black spruce seeds when presented with both
[2,3].  In Arizona each red squirrel was estimated to consume the seeds
of 42,000 to 131,000 pine cones per year [27,47].  On New Brunswick jack
pine sites, red squirrels consumed at least 47 cones per day [7].

In summer a larger array of foods is eaten, including elm (Ulmus spp.)
and maple (Acer spp.) seeds, raspberries (Rubus spp.) and other fruits,
and green cones of pines, Douglas-fir, hemlock, cedar, and larch (Larix
spp.).  Some insects and nestling birds are also consumed [25].  In New
Hampshire red squirrels were observed preying on the eggs and young of
black-throated blue warblers (Dendroica caerulescens) [30].  Red
squirrels lap sap from trees damaged by yellow-bellied sapsuckers
(Sphyrapicus varius), and from other tree wounds [17].  They were also
observed licking sap and dried sugar from sap wells drilled by red-naped
sapsuckers (S. nuchalis) in Colorado [8].  In Vermont red squirrels were
observed biting holes in hardwood trees at periods associated with sap
flow.  Sugar maple (Acer saccharum) was chosen more often than any other
tree.  Rather than licking sap immediately, the red squirrels left the
fresh bite and returned at a later time, licking sap flows that had time
to evaporate into more concentrated sugar syrup or dried sugar.  Sugar
spread by the researcher onto tree trunks did not immediately attract
red squirrels; it was inferred that red squirrels returned intentionally
to sap flows they had created [17].

The diet of the endangered Mount Graham red squirrel is not well known,
but is assumed to be similar to that of other red squirrels;
requirements include conifer seeds (mainly Engelmann spruce and
subalpine fir) and mushrooms [28].

In western North America cones are cached by red squirrels in a large
central location, often referred to as a midden (this type of food
storage is known as larderhoarding).  Middens also contain other foods
such as seeds of other plant species, and mushrooms.  Secondary middens
are also developed, usually at the base of a tree or tree cavity, but
are usually much smaller then the main midden [18,27].  Mushrooms are
sometimes left in tree branches and cached after they have dried [13].
It was suggested that larderhoarding may be a response to intense
predation in the winter; there is less movement involved in retrieving
cones from a cache than in searching for cones all winter [7].

In Wyoming red squirrels spent most of their foraging time in whitebark
pine forests finding and eating whitebark pine seed from cones or
recovering dropped whitebark pine seed.  Cone harvesting may begin as
early as July 13 and cone caching usually begins by August 4.  Red
squirrels often leave cones on the ground below the tree for up to 3
days before caching them [18].  In Colorado red squirrels appear to
prefer Douglas-fir cones over ponderosa pine cones; this may be a result
of interspecific competition with Abert's squirrels which require
ponderosa pine cones and bark [11].  In the Southwest commonly eaten and
preferred seeds include those of Douglas-fir, blue spruce, Engelmann
spruce, and white fir.  Ponderosa pine seed is occasionally eaten in
Arizona [31].

In eastern North America red squirrels in conifer-dominated forests have
diets similar to those in western North America.  In Maine red squirrels
remove northern white-cedar (Thuja occidentalis) branchlets and cones in
the fall, and consume branchlets with reproductive buds in the spring
[4].  Winter foods include terminal buds of conifers, boxelder (Acer
negundo) and red pine (Pinus resinosa) seeds, buds and sap of red maple
(A. rubrum), gray birch (Betula populifolia) and sugar maple, corn (Zea
mays), seeds of basswood (Tilia americana), sugar maple, silver maple
(A. saccharinum), Norway maple (A. platanoides), northern red oak
(Quercus rubra) and other oaks, hickory nuts, and butternuts (Juglans
cinera).  Eastern hemlock (Tsuga canadensis) cones are a staple item in
some areas.  Other winter foods include yellow-poplar (Liriodendron
tulipifera) and sycamore (Platanus occidentalis) seeds, fruits of
staghorn sumac (Rhus typhina) and smooth sumac (R. glabra), and bark.
In April and May red squirrels consume tree buds and flowers,
particularly those of American elm (Ulmus americana), sugar maple,
silver maple, Norway maple, northern red oak, and butternut [13,25,32].

In New Brunswick red squirrels are scatterhoarders rather than
larderhoarders; food is stored in small amounts in many places rather
than in one central midden.  Red squirrels stored cones from both
serotinous and nonserotinous species:  jack pine in central Ontario;
black, white, and red spruce (Picea rubens) in New Brunswick; and black
and red spruce in Maine.  Cached cones are not sufficient for an entire
winter food supply; however, jack pine cones remain closed for at least
1 year and are retained on the tree for up to 7 years and therefore
provide a steady supply of winter food [7].  In Pennsylvania researchers
could not locate cone caches in marginal red squirrel habitat dominated
by aspens (Populus spp.).  Red squirrels used a central location for
consuming cones; these feeding areas have been identified by the remains
of up to 103 cones [50].


PREDATORS : 
The main predators of red squirrels in Alberta are raptors, probably
principally northern goshawk (Accipiter gentilis) [24].  Other red
squirrel predators include red-tailed hawk (Buteo jamaicensis), red fox
(Vulpes vulpes), bald eagle (Halieaatus leucocephalus), marten (Martes
americana), lynx (Lynx lynx) and ermine (Mustela erminea) [13,44].  Lynx
prey slightly more heavily on red squirrels in summer than winter (2% of
lynx winter diet, 9% of summer diet) [13].  Red squirrels comprised 5.6
percent of 36 prey deliveries to northern goshawk nests and 17.5 percent
of pellets (in 8 nests).  More than 100 red squirrels were taken per
season by a single pair of breeding northern goshawks [31].

In Yellowstone National Park martens use the subnivean zone to get to
their prey which includes red squirrel.  Red squirrels comprised 25
percent by volume of marten scats [37].


MANAGEMENT CONSIDERATIONS : 
Red squirrels are considered pests in some areas where they consume a
large proportion of available conifer seeds.  It has been suggested that
they interfere with natural regeneration of conifers by removing most of
the seed crop; this is particularly detrimental in years with poor cone
crops [12,13,51].  Cached seed and cones do not usually germinate; a
seed fungus (Caloscypha fulgens), which appears to prevent germination
and rotting of seeds, is encouraged by the moist, cool conditions
usually found in red squirrel cache sites [53,54].  In Newfoundland red
squirrels are a recent introduction and have become a serious threat to
black spruce cone harvests for commercial seed production [48].  Red
squirrels clip (and often consume) terminal buds and peel the bark of
trees, occasionally girdling stems.  Gnawing damage to trees sometimes
causes canker formation [13].  In Arizona red squirrels harvested more
than 80 percent of limber pine (Pinus flexilis) cones before the cones
opened (making the seeds unlikely to germinate even if they are not
consumed); in open sites where red squirrels were absent more than 70
percent of cones opened on the trees [9].

In Newfoundland harvesting black spruce cones in August or September is
recommended in order to anticipate removal of cones by red squirrels
[48].  In central British Columbia thinning of 20-year-old lodgepole
stands resulted in a reduction in red squirrel populations but did not
appreciably lower the amount of tree damage inflicted by red squirrels
gnawing on bark [41].

Red squirrels and other mycophagous species probably play an important
role in the dispersal of the spores of mycorrhiza-forming fungi and
therefore benefit conifer reproduction [26].  Red squirrel middens are a
source of conifer seed for forestry in some western states [12,13].

Habitat Management:  Red squirrels are dependent on mature conifers for
food and cover.  Conifer plantings in suburban areas tend to encourage
red squirrels.  Red squirrels will use nest boxes if they are placed in
suitable habitat [13].  Vahle and Patton [27,47] recommended maintenance
of areas with closely spaced groups of trees of different ages and sizes
for red squirrel habitat.  Conifers larger than 15 inches (38 cm) d.b.h.
are necessary for cone production; at least three or four large trees
per acre are needed.  Timber harvest using group selection promotes
habitats favored for red squirrel cache sites [47].  Reynolds and others
[31] listed specific management recommendations for red squirrels in the
Southwest in conjunction with maintenance of northern goshawk prey base.

Black bears (Ursus americanus) damaged trees adjacent to Mount Graham
red squirrel middens more often than at random locations.  This damage
frequently kills the tree.  Death of the tree results in loss of cone
production, but it also provides snags for nest cavities and storage
sites [39].  The endangered grizzly bear (U. arctos horribilis)
excavates red squirrel cone caches in whitebark pine stands; this is an
important grizzly bear food source in some areas.  Grizzly bear habitat
management includes encouragement of both whitebark pine and red
squirrel [56].

Red squirrels are economically important furbearers in Canada [19,53].
More red squirrels are taken but the total value is less than that of
other furbearers [53].

Parasites and diseases of red squirrels were summarized by Layne [25]
and Flyger and Gates [13].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Tamiasciurus hudsonicus | Red Squirrel