Sciurus stramineusGuayaquil squirrel

Geographic Range

Sciurus stramineus is found in South America from southwestern Ecuador to northern Peru, including the Noroeste Biosphere Reserve. These squirrels are considered rare in Peru because they only occupy the most northern parts of the country. They are found along the Gulf of Guayaquil as well as along the Andean slope to Cajamarca. The Andean slope has an elevation ranging from sea-level to 2000 m. These are the only squirrels endemic to the area, except for north of Guayaquil, Ecuador where they share a range with Sciurus granatensis (the red-tailed squirrel). Sciurus stramineus was introduced into Lima, Peru and has been observed living freely in the Parque de Las Leyendas Zoo. They have also been spotted in the parks of Lima including Surco, San Isidro, San Miguel, and Chaclacayo as well as the green areas within Pontificia Universidad Católica del Peru. (Allen, 1915; Emmons and Feer, 1990; Jessen, et al., 2010; Leal-Pinedo and Linares-Palomino, 2005; Merrick, et al., 2012; Montes, et al., 2011; Thorington Jr., et al., 2012)


Guayaquil squirrels are arboreal and live in trees found in both mature and secondary forests, as well as coffee plantations. The forests are evergreen, deciduous and semi-deciduous. The forests in the southern range are humid and montane. These forests are located at an elevation of 1400 to 2000 m along the western Andean slope. The northern range forests are humid and dry, and located at sea level. These forests have vegetation that consists mostly of prickly plants, bushes, and herbaceous plants. (Emmons and Feer, 1990; Jessen, et al., 2010; Merrick, et al., 2012; Thorington Jr., et al., 2012)

In the Cerros de Amaotape National Park near coastal northern Peru, S. stramineus lives in an elevation of 200 to 1613 m in forests. These forests are montane with thorny vegetation, dry, and very dry tropical forests. The species of plant in this park include Prosopis juliflora, Loxopterygium huasango, Capparis angulate, Caesalpinea corymbosa, Bombax species, and Tillandsia species. Along the northeastern Peruvian coast, dry plains and forests are inhabited by Guayaquil squirrels. The dominant species of trees of this region are the Acacia macracantha, and the Prosopis pallida. (Erdmann, et al., 2008; Leal-Pinedo and Linares-Palomino, 2005; Suarez-Davalos, et al., 2010)

Closer to human populations, Guayaquil squirrels have been spotted in the lowlands of Ecuador in communities including Portoviejo County in the Manabí province, and Maconta Abajo. These areas include a mix of forest, corn crops, and papaya crops. The forests in this area are semi-deciduous with a dense, deciduous, groundcover and a thin tree population. The humidity in June and July in Maconta Abajo has been seen to reach up to 97%. The large trees of the urban landscape in Lima, Peru are also known habitat for S. stramineus, since they can thrive in urban landscapes, as well as in captivity. (Grijalva, et al., 2012; Jessen, et al., 2010; Merrick, et al., 2012; Weigl, 2005)

  • Range elevation
    2000 (high) m
    6561.68 (high) ft

Physical Description

In general, Guayaquil squirrels are large squirrels with four pairs of mammae; long, thin, grey tails; long, narrow, black ears; and five digits on their hind feet. There are two distinct color morphs in this species. In the early to mid-1900s these morphs were described as four separate subspecies, however S. stramineus is now considered to be monotypic. The first morph is found in the lowlands of Ecuador, where the squirrels have shoulders that appear grey due to a coarse mix of white and black fur. Their rumps and tails are a dull orange with patches of black and their underparts are a reddish to dull brown while their heads are black. Their feet can be white or black and their tails are black with white tips. This morph used to be described as the subspecies Sciurus stramineus stramineus and Sciurus stramineus guayanas. Sciurus stramineus stramineus was described as having darker, yellowish grey upperparts while S. stramineus guayanus was described as having paler upperparts and a wash of grey on their underparts. The second color morph is found in Peru and the southern highlands of Ecuador. This morph of S. stramineus has pale grey underparts and tails caused by a heavy frosting of white hairs in their black fur. Their rumps are either a buff, faint, or bright orange and the neck area behind their ears is either pure white or pale yellow. The feet of this morph are black. This morph used to be divided into the subspecies Sciurus stramineus nebouxii and Sciurus stramineus zarumae. The paler version of this morph was considered to be S. stramineus nebouxii, while the darker version was considered to be S. stramineus zarumae. There are often spots of white hair that are longer than the rest of the fur found on both morphs. The Peruvian and south Ecuador highland morph is the morph seen in the Parque de Las Leyendas Zoo. (Allen, 1915; Alston, 1878; Eisenberg and Redford, 1999; Ellerman, 1940; Emmons and Feer, 1990; Jessen, et al., 2010; Merrick, et al., 2012; Thorington Jr., et al., 2012)

The mass of Guayaquil squirrels ranges from 460 to 495 g. The length of the head and body range from 180 to 320 mm with the average female head and body length being 250.3 mm and the average male head and body being 251.3 mm in length. The tail length ranges from 250 to 330 mm with the average female tail length being 292.1 mm and the average male tail length being 275.4 mm. The hind foot of S. stramineus ranges from 50 to 65 mm in length while the length of the ear ranges from 38 to 39 mm. (Allen, 1915; Eisenberg and Redford, 1999; Emmons and Feer, 1990; Hayssen, 2008; Merrick, et al., 2012; Thorington Jr., et al., 2012)

Sciurus stramineus is the only South American Sciurus species that is indistinguishable from the North American species of Sciurus when looking at the jaw shape and arm lever. These squirrels have a skull that is not highly convex with a length ranging from 58.2 to 60 mm. The breadth of the braincase ranges from 22 to 23.5 mm. They have a snub-nosed appearance due to a short rostrum. Their nasals are very broad, but short, making up only approximately 22% of the skull length and only 60% of the interorbital breadth. The dimensions of the nasals have a range of 15 to 18 mm by 8 to 9 mm, while the interorbital breadth ranges from 18 to 20 mm and the postorbital breadth ranges from 17 to 18 mm. Sciurus stramineus has a highly developed, broad zygomatic arch with a breadth ranging from 32 to 33mm. They have heavy dentition with their maxiliary toothrow ranging from 10 to 10.5 mm and the diastema ranging from 13.2 to 14.5 mm. Their dental formula is 1/1 0/0 1/1 3/3 = 20 and their teeth have smooth enamel. (Allen, 1915; Ellerman, 1940; Swiderski and Zelditch, 2010; Thorington Jr., et al., 2005)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    460 to 495 g
    16.21 to 17.44 oz
  • Range length
    430 to 650 mm
    16.93 to 25.59 in


Nothing is known about reproduction in S. stramineus. However, conclusions can be drawn from the mating systems of Sciurus carolinensis and Sciurus niger, which are the two species most closely related to S. stramineus. These two species are polygynandrous and have an estrus that lasts less than one day. There are two main breeding seasons. It is possible for mating to occur outside of these seasons, however the occurrence is greatly reduced. Sciurus carolinensis and S. niger experience a period from August to October where the male testes size is significantly decreased, reducing the chances of successful breeding. Since it is a South American species, S. stramineus may or may not have the same period of reduced testes size. (Brown and Yeager, 1945; Kirkpatrick and Hoffman, 1960; Koprowski, 1993; Koprowski, 1994a; Koprowski, 1994b; Moore, 1957; Oshida and Masuda, 2000; Webley and Johnson, 1983)

The mating system in S. stramineus is not known, but conclusions can be drawn from commonalities in its two closest relatives, S. niger and S. carolinensis. Both S. niger and S. carolinensis form a linear dominance hierarchy amongst males. Four to seven males will participate in an estrus, with the dominant male and subordinate satellite males all chasing a female. The dominant male will attempt to copulate with the female but the copulation is often interrupted by either the female escaping or another male interrupting. If the copulation by the dominant male is completed, the male will introduce a copulatory plug and attempt to guard the female. Usually, however, the female will remove the copulatory plug and repeat this process with another male. Most copulation occurs in trees. (Koprowski, 1992; Koprowski, 1993; Koprowski, 1994a; Koprowski, 1994b; McCloskey and Shaw, 1977; Oshida and Masuda, 2000)

Nothing is known about the reproduction of S. stramineus. However, conclusions can be drawn from the commonalities in the general reproductive behaviors of S. carolinensis and S. niger. S. carolinensis and S. niger have two breeding seasons. Females can breed during both seasons, however most only breed during one season a year. Females usually start reproducing around 15 months of age, while males reach sexual maturity around 10 or 11 months. Gestation in S. carolinensis and S. niger is 44 to 45 days, and most litter sizes range from 2 to 4, however a maximum of 8 and a minimum of 1 is possible. The neonates are born naked, with vibrissae and well-developed claws. Birth mass averages 13 to 18 g. Birth head and body length averages 50 to 60 mm. Juveniles will begin weaning after about 2 months and will become independent after 3 to 4 months. During the weaning time juveniles will leave the nest to forage for food, such as seeds and buds. (Allen, 1942; Barkalow, Jr., et al., 1970; Brown and Yeager, 1945; Harnishfeger, et al., 1978; Kirkpatrick and Hoffman, 1960; Koprowski, 1994a; Koprowski, 1994b; McCloskey and Shaw, 1977; Oshida and Masuda, 2000; Webley and Johnson, 1983)

  • Breeding interval
    Guayaquil squirrels likely breed once or twice a year.
  • Range number of offspring
    1 to 8
  • Average number of offspring
    2 to 4
  • Average gestation period
    44 to 45 days
  • Average weaning age
    2 months
  • Average time to independence
    3 to 4 months
  • Average age at sexual or reproductive maturity (female)
    15 months
  • Average age at sexual or reproductive maturity (male)
    10 to 11 months

Nothing is known about the reproduction of S. stramineus. Conclusions can be drawn from the few commonalities in the parental investment of S. carolinensis and S. niger. These squirrels have altricial young, and female parental care. (Brown and Yeager, 1945; Koprowski, 1994a; Koprowski, 1994b; Oshida and Masuda, 2000)


The Guayaquil squirrel known to live the longest in captivity died at 7.3 years old. The squirrel lived from August 8, 1996 to December 19, 2003 at the Zoologico Nacional de Santiago in Chile. (Weigl, 2005)

  • Range lifespan
    Status: captivity
    7.3 (high) years


Sciurus stramineus is a diurnal species. They build their nest in large, tall, non-palm trees. The nests are round and made of leaves. These nests are located in the tree canopies above 5 m, and can be as high as 20 m. The most common nest height is 8 m. The nests are loose in construction and have a diameter of approximately 30 cm. (Emmons and Feer, 1990; Grijalva, et al., 2012; Suarez-Davalos, et al., 2010; Thorington Jr., et al., 2012)

These squirrels also willingly interact with people. They have been known to approach people and are quite bold. They have adapted to an urban environment, and are often seen walking on telephone wires to cross streets. (Jessen, et al., 2010; Merrick, et al., 2012)

Home Range

Home range is not reported in the literature.

Communication and Perception

Nothing is known about communication and perception in S. stramineus.

Food Habits

Plants are the main source of food for Guayaquil squirrels. They forage on the ground as well as in the tree canopies of the forest. They mainly consume seeds. In Parque de Las Leyendas Zoo they are opportunistic feeders, feeding on the same diet of seeds, fruits, and vegetables as the captive animals, as well as the ornamental flowers found in the zoo. Sciurus stramineus have been observed preying on the eggs of birds, including the eggs of Phytotoma raimondii (the endangered Peruvian plantcutter). (Erdmann, et al., 2008; Jessen, et al., 2010; Merrick, et al., 2012; Nolazco and Roper, 2014; Thorington Jr., et al., 2012)

  • Animal Foods
  • eggs
  • Plant Foods
  • seeds, grains, and nuts
  • fruit
  • flowers


The only known predator of S. stramineus is Lycalopex sechurae (Sechura foxes). (Erdmann, et al., 2008)

  • Known Predators
    • Sechura foxes (Lycapolex sechurae)

Ecosystem Roles

Guayaquil squirrels and their nests are host to parasitic and commensal species. The flea Polygenis litargus and an Ambylomma species of tick, closely related to Ambylomma maculatum, are two of these species. Assassin bugs, Rhodnius ecuadoriensis, are found in the nests of these squirrels and likely use the squirrels as a food source. The rate of infestation by this insect ranged from 13.6% to 40% of nests studied, with the highest infestation seen in El Guino. The average infestation rate most recently observed in 2012 was 21.1% of nests. Rhodnius ecuadoriensis is a vector of Trypanosoma cruzi. Guayaquil squirrels are also asymptomatic carriers of a Leptospira species of bacteria. Wild-rodent (sylvatic) plague and, in captive squirrels, Plasmodium infections are found as well. (Garnham, 1949; Grijalva and Villacis, 2009; Grijalva, et al., 2012; Jordan, 1950; Montes, et al., 2011; Need, et al., 1991; Pollitzer, 1952)

Commensal/Parasitic Species
  • fleas (Polygenis litargus)
  • tick species in the genus (Ambylomma)
  • assasin bugs (Rhodnius ecuadoriensis)
  • malarial parasites (Plasmodium)

Economic Importance for Humans: Positive

Guayaquil squirrels are captured and sold as pets in South America and as far away as Japan. They are also hunted for food. (Duckworth and Koprowski, 2008; Oshida and Masuda, 2000; Pacheco, 2002)

Economic Importance for Humans: Negative

Rhodnius ecuadoriensis is found in Sciurus stramineus nests and is a known vector of Chagas disease caused by Trypanosoma cruzi. Rhodnius ecuadoriensis has been found in higher rates in squirrel’s nest than in that of mice and birds. The proliferation of Chagas disease in Sciurus stramineus is likely due to passive transportation from infected humans. (Grijalva and Villacis, 2009; Grijalva, et al., 2012; Suarez-Davalos, et al., 2010)

The sylvatic plague infecting S. stramineus is a variant of plague that affects domestic rodents. Rodents can pass the plague on to humans. (Garnham, 1949; Pollitzer, 1952)

  • Negative Impacts
  • injures humans
    • carries human disease

Conservation Status

The IUCN Red List lists S. stramineus as “Least Concern.” The major threat to these squirrels is the destruction of their habitat due to woodcutting and agriculture. The ranking is due to a large population and wide distribution. The propensity for secondary forests as a habitat also allows the Guayaquil squirrels to survive in a changing habitat, which aids in their conservation. These squirrels are thought to have the potential to help understand the biological changes of their geographic range when observed with other species because they are endemic to South America and are abundant enough to be observed. However, little is known about their populations nor the impact of the pet trade on their populations. (Duckworth and Koprowski, 2008; Emmons and Feer, 1990; Pacheco, 2002; Peralvo, et al., 2007; Thorington Jr., et al., 2012)


Melissa Hahn (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Tanya Dewey (editor), University of Michigan-Ann Arbor.



living in the southern part of the New World. In other words, Central and South America.

World Map


living in landscapes dominated by human agriculture.


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.


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.


an animal that mainly eats meat


uses smells or other chemicals to communicate

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

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.

female parental care

parental care is carried out by females


union of egg and spermatozoan


A substance that provides both nutrients and energy to a living thing.


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


an animal that mainly eats seeds


An animal that eats mainly plants or parts of plants.


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).


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

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


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

pet trade

the business of buying and selling animals for people to keep in their homes as pets.


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


"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

seasonal breeding

breeding is confined to a particular season


remains in the same area


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


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


uses touch to communicate


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).


Living on the ground.


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


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


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


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