Sciurus aestuans 39year old. Perhaps the most striking and popularized aspect
of the biology of Abert’s squirrels is their dependence,
sometimes considered obligatory, on a single tree species—
Pinus ponderosa. While this dependence on ponderosa
pines is overstated, Abert’s squirrels clearly are unique in
their ability to utilize phloem as an important food source
during periods of winter food shortages, in part due to a
lengthened digestive tract. Individuals clip 2–5 cm lengths
of small twigs from the distal portion of branches, strip
the bark, and eat the phloem. The completely stripped
clippings are discarded, and they have been used to esti-
mate the density and document the presence or absence of
this species. Squirrels select trees with reduced chemical
defenses when feeding on phloem. Abert’s squirrels also
consume a wide variety of tree seeds—including those of
pine (Pinus), true fi rs (Abies), Douglas fi r (Pseudotsuga men-
ziesii), and oaks (Quercus)—in addition to buds, fungi, in-
sects, bone, and (occasionally) soil. S. aberti does not cache
seeds. However, they are known to pilfer from other spe-
cies that do store seeds, such as Tamiasciurus hudsonicus.
Abert’s squirrels overlap considerably in space with
their neighbors. Home ranges are relatively large, often
greater than 20 ha, with male ranges sometimes larger than
those of females, perhaps due to mate searching. S. aberti
nests primarily in dreys, constructed of leaves and twigs
within the forest canopy. The dense growth of twigs
(known as witch’s brooms) caused by parasitic mistletoes
are commonly used to anchor and obscure nests. Much less
frequently, Abert’s squirrels employ cavities as nests. Both
nest types are used to rear the young and serve as noctur-
nal nests. Nests are located in larger and taller trees with
canopies connected to adjacent trees. The nests are found
within more dense stands of trees, rather than being situ-
ated at random in the surrounding area. Individuals change
nests regularly and maintain several active nests simultane-
ously. Communal nesting in mixed-sex assemblages occurs
frequently in winter but is rare in the warmer months. Ab-
ert’s squirrels are not highly vocal, but they do use a gruff
low-pitched barking alarm call when startled or after de-
tecting predators such as raptors, foxes, or bobcats (Lynx
rufus). This species is hunted for food and sport throughout
its range. Due to the low human population densities
within the range of this species, S. aberti is of little eco-
nomic value or detriment; however, their practice of clip-
ping branch tips can signifi cantly reduce cone availability.
The introduction of Sciurus aberti to isolated mountain
ranges in Arizona may have negatively impacted popula-
tions of endemic native tree squirrels, such as Sciurus arizo-
nensis and Tamiasciurus hudsonicus grahamensis.
general references: R. Davis and Brown 1988; Edelman
and Koprowski 2005, 2006; Lamb et al. 1997; M. A. Snyder
1992, 1993; Yensen and Valdés-Alarcón 1999.Sciurus aestuans (Linnaeus, 1766)
Guianan Squirreldescription: The Guianan squirrel has an olivaceous gray
dorsum grizzled with brown and yellow. The eye ring is
pale yellowish brown, and sometimes there is a pale buff y
yellow postauricular patch. The upper surface of the tail is
the same color as the dorsum, with a rufous and more vari-
able underside. The venter is white to cream to buff to yellow-
ish. Albinism and melanism occur but are not common.size: Both sexes—HB 160–186 mm; T 163–250 mm; Mass
160–380 g.distribution: This species can be found throughout much
of Brazil, as well as in Colombia, Venezuela, Guyana, Suri-
name, French Guiana, and Argentina.geographic variation: Ten subspecies are recognized.S. a. aestuans—north of the Amazon, in Colombia, Vene zuela,
Guyana, Suriname, French Guiana, and Brazil. This form