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Sciurus nayaritensisMexican fox squirrel

By James Stribrny

Geographic Range

Mexican fox squirrels (Sciurus nayaritensis), have a limited distribution in pine oak forests of the Chiricahua Mountains in Arizona and the Sierra Madre Occidental Mountains of Mexico, as far south as Jalisco. (Best, 1995; Lee and Hoffmeister, 1963)

Habitat

Mexican fox squirrels are primarily found in riparian habitats where sycamores, ashes, walnuts, and large evergreen oaks grow. The greatest abundance of S. nayaritensis is found in the upper Sonoran zone, located in canyon bottoms that have dense concentrations of trees and shrubs. They tend to avoid oak-cover slopes near the canyons, except when oak mast is plentiful. In the Chiricahua Mountains, S. nayaritensis occur in elevations that range from 1,560 to 2,700 m. In this location, they prefer open apache pine-oak, rather than dense stands of trees. In the San Luis Mountains, S. nayaritensis inhabits areas 1,700 to 2,100 m in elevation. Sciurus nayaritensis are common in the Durango, in oak-pine forests above 2,100 m in elevation. The San Luis Mountains harbor S. nayatirensis at elevations of 1,700 to 1,800 m, where they feed and take shelter in silverleaf oaks. ("Sciurus nayaritensis", 1890; Lee and Hoffmeister, 1963; Linzey, et al., 2008; Pasch and Koprowski, 2005)

  • Range elevation
    1560 to 2700 m
    5118.11 to 8858.27 ft
  • Average elevation
    1650-1950 m
    ft

Physical Description

Sciurus nayaritensis have bushy tails that are tan to yellow. They have side colorations that are reddish or ochraceous. Their pelage is thick and soft, with long underfur. Legs and feet are reddish or ochraceous in color, with naked soles that are dark purplish. Their coat coloration varies between ranges, seasons, and subspecies. There are three subspecies of Sciurus nayaritensis, Sciurus nayaritensis chiricahuae, Sciurus nayaritensis apache, and Sciurus nayaritensis nayaritensis. The subspecies differ mostly in coloration. Sciurus nayaritensis chiricahuae differs from S. n. apache, primarily in the darkness of the ochraceous underparts, orbital ring and post auricular areas. Sciurus nayaritensis chiricahuae differs from S. n. nayaritensis in color dorsally and ventrally, and also their dark-ochraceous underparts, orbital rings, and post auricular areas. Another feature differentiating S. n. chiricahuae and S. n. nayaritensis is the skull of S. n. chiricahuae, which is shorter and broader, with a rostrum laterally expanded at the distal ends of the nasal. Metabolic rate is unknown for Sciurus nayaritensis, but a closely related species, Sciurus aberti, has a basal metabolic rate of 0.003849 W/g. (Best, 1995; Lee and Hoffmeister, 1963)

  • Sexual Dimorphism
  • female larger
  • Average mass
    684 male, 707 female g
    oz
  • Range length
    496 to 613 mm
    19.53 to 24.13 in
  • Average length
    554 mm
    21.81 in
  • Average basal metabolic rate
    0.003849 W/g cm3.O2/g/hr

Reproduction

Mating systems within family Sciuridae include polygynous, polyandrous, and polygynandrous, but no specific mating behavior has been observed in Sciurus nayaritensis. (Best, 1995)

Sciurus nayaritensis have a low reproductive potential, which leaves the species with a limited ability to recover quickly from disturbance events. Due to the lack of research on the reproductive process for S. nayaritensis, it may be assumed that they are similar to the closely related sympatric species, Albert's squirrels (Sciurus aberti), Mexican gray squirrels (Sciurus aureogaster), and Collie's squirrels (Sciurus colliaei). Albert's squirrels are able to mate before they are a year old and reproduce 1 to 2 times a year, April through May. After approximately a 43-day gestation period, they have a litter of 1 to 3 young, each weighing approximately 12 grams. Young are weaned in approximately 76 days. ("An Age entry for Sciurus aberti", 2012; Pasch and Koprowski, 2005)

  • Breeding interval
    Mexican fox squirrels breed 1 to 2 times a year.
  • Breeding season
    Their breeding season is in April and early May.
  • Range number of offspring
    1 to 3
  • Average gestation period
    43 days
  • Average weaning age
    76 days
  • Average time to independence
    Unkown days
  • Average age at sexual or reproductive maturity (female)
    327 days

Females are responsible for all of the care of their young, males have no parental investment. There is no information about Mexican fox squirrels, but it is likely that their close relative, Albert's squirrels, are very similar. Female Albert's squirrels wean their young after approximately 76 days; after which, young eat other foods, including tree seeds. ("An Age entry for Sciurus aberti", 2012)

Lifespan/Longevity

The lifespan of Mexican fox squirrels has not been recorded; however, a close relative, Sciurus aureogaster, was born in the wild and survived to be 11.5 years old in captivity. Due to the lack of information on either species, the lifespan data is far from conclusive. ("An Age entry for Sciurus aberti", 2012)

  • Average lifespan
    Status: wild
    Unknown years
  • Average lifespan
    Status: wild
    Unknown years
  • Average lifespan
    Status: captivity
    Unknown years

Behavior

Mexican fox squirrels live and rest in trees and are diurnal animals that leave their nests after dawn and return before dusk. Mexican fox squirrels spend most of their time on the ground and are not agile in trees. They are not totally built for arboreal life and are clumsy and awkward when climbing up and down tree trunks and along branches. The young routinely fall out of trees and even the adults are not adept climbers. They are secretive in nature and can be difficult to find, especially in the early summer, when females are pregnant or nursing their young. They are also difficult to find in the winter when forests are bare and open. (Best, 1995; "Sciurus nayaritensis", 2012)

  • Range territory size
    Female: 0.1 Male: 0.3 to Female: 0.2 Male: 0.4 km^2
  • Average territory size
    Female: 0.15 Male: 0.35 km^2

Home Range

Home ranges of Mexican fox squirrels vary between males and females. Males have larger home ranges expanding 30 to 40 hectares. Females, on the other hand, have home ranges of 10 to 20 hectares. During the mating season, home ranges shrink slightly. (Pasch and Koprowski, 2006)

Communication and Perception

Mexican fox squirrels do not usually vocalize. When they do, it is generally due to disturbance. Their vocalization is usually accompanied by a visual warning, such as flicking their tail. In some subspecies, tail flicking is not accompanied by vocalizations. (Best, 1995)

Food Habits

Mexican fox squirrels are foragers that do not cache food or bury nuts like other members of Family Sciuridae. In the Chiricahua Mountains, Mexican fox squirrels eat pine and Douglas fir seeds, along with acorns and walnuts. When oak mast and other tree seeds are unavailable, they eat roots, bulbs, and buds. In the Durango, Mexican fox squirrels mainly survive by eating pine seeds. Berries, hypogeous fungi, and a few small insects and larvae are occasionally a part of Mexican fox squirrels diet. Rarely, Mexican fox squirrels also eat bark, leaves, and lichens, representing a proportion of less than 0.003 of their total diet. They may also occasionally rob eggs and nestlings from bird nests and eat invertebrates when rummaging on the forest floor. Sciurus nayaritensis chiricahuae may avoid camping sites and other areas that contain human food. They seem to only be attracted to native foods. (Best, 1995; Goldman, 2011; Koprowski and Corse, 2001; "Sciurus nayaritensis", 2012)

  • Animal Foods
  • birds
  • eggs
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms
  • Plant Foods
  • leaves
  • roots and tubers
  • wood, bark, or stems
  • seeds, grains, and nuts
  • lichens
  • Other Foods
  • fungus

Predation

Mexican fox squirrels have similar predators to other members of Family Sciuridae. Their known predators include raptors, snakes, small predatory mammals, and humans. (Best, 1995; Kneeland, et al., 1995)

If caught by surprise, Mexican fox squirrels remain motionless to stay undetected by potential predators. If startled or caught in the open, they will retreat to the nearest or tallest tree, where they will hide and remain motionless for more than 45 minutes, or as long as the danger is perceived. Mexican fox squirrels are usually quiet, but will vocalize a warning once they are safely in a tree. Their alarm barks are raspy and gruff and sometimes followed by a whirring screech or scream. A subspecies of S. nayaritensis, S. n. apache are more vocal than S. n. chiricahuae and routinely screams in response to human or hawk activity. Whereas, when S. n. chiricahuae faces disturbance, it flicks its tail but does not vocalize. (Best, 1995; Goldman, 2011; Kneeland, et al., 1995; "Sciurus nayaritensis", 2012)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Mexican fox squirrels do not have a big impact on the ecosystem, but are seed predators and reduce the fitness of the trees on which they feed. They do not cache food, so seed dispersal is limited. They have a commensalistic interaction with oaks and pines, where they make their nests. (Pasch and Koprowski, 2005; "Sciurus nayaritensis", 2012)

Species Used as Host
  • Oak tree (Quercus)
  • pine trees (Pinus)
Mutualist Species
  • none
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Mexican fox squirrels have been exploited by humans in the past for food. They are not a popular game species, but are still hunted in some areas, while in other areas, such as the Chiricahuas, hunting is prohibited. (Goldman, 2011; Pasch and Koprowski, 2005)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

Besides carrying parasites such as ticks, lice, and fleas that can be transmitted to humans, Mexican fox squirrels do not have a negative impact on humans. However, they are carriers of the rabies virus, and could transmit the virus to humans or household pets. Toxoplasma gondii can be transmitted to humans from eating undercooked Sciurus nayaritensis meat. Toxoplasma gondii is usually present, but provides no symptoms. It can cause toxoplasmosis, which can be a serious illness in humans when symptoms are shown. (Alvarado-Esquivel, et al., 2008; "Toxoplasmosis", 2005)

Conservation Status

Sciurus nayaritensis is listed as a category-two species by the United States Department of the Interior, Fish and Wildlife Service. Category-two species are candidates for official listing as endangered or threatened. (Best, 1995; "Chiricahua Nayarit squirrel (Sciurus nayaritensis chiricahuae)", 2012)

Contributors

James Stribrny (author), University of Alaska Fairbanks, Laura Prugh (editor), University of Washington, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

Glossary

Neotropical

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

World Map

acoustic

uses sound to communicate

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.

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

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.

female parental care

parental care is carried out by females

food

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

forest

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

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

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.

riparian

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

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

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.

visual

uses sight to communicate

viviparous

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

References

Human Ageing Genomic Resources (HAGR). 2012. "An Age entry for Sciurus aberti" (On-line). An Age: The Animal Ageing and Longevity Database. Accessed December 10, 2012 at http://genomics.senescence.info/species/entry.php?species=Sciurus_aberti.

Human Ageing Genomic Resources (HAGR). 2012. "An Age entry for Sciurus aureogaster" (On-line). An Age: The Animal Ageing and Longevity Database. Accessed December 10, 2012 at http://genomics.senescence.info/species/entry.php?species=Sciurus_aureogaster.

U.S. Fish & Wildlife Service. 2012. "Chiricahua Nayarit squirrel (Sciurus nayaritensis chiricahuae)" (On-line). U.S Fish & Wildlife Service Species Profile. Accessed November 16, 2012 at http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=A0EH.

Smithsonian. 2012. "Sciurus nayaritensis" (On-line). Smithsonian National Museum of Natural History. Accessed November 16, 2012 at http://www.mnh.si.edu/mna/image_info.cfm?species_id=302.

Bucknell University. 1890. "Sciurus nayaritensis" (On-line). Wilson & Reeder Mammal Species of the World third edition. Accessed November 16, 2012 at http://www.bucknell.edu/msw3/browse.asp?s=y&id=12400172.

United States Department of Agriculture. 2005. "Toxoplasmosis" (On-line). United States Department of Agriculture. Accessed November 16, 2012 at http://www.ars.usda.gov/main/docs.htm?docid=11013.

Alvarado-Esquivel, C., H. Cruz-Magallanes, R. Esquivel-Cruz, S. Estrada-Martinez, M. Rivas-Gonza ́lez, O. Liesenfeld, S. Martinez-Garcia, E. E. Ramirez, A. Torres-Castorena, A. Castaneda, J. Dubey. 2008. Seroepidemiology of Toxoplasm gondii Infection in Human Adults From Three Rural Communities in Durango State, Mexico. The Journal of Parasitology, Vol. 94 No. 4: 811-816. Accessed November 16, 2012 at http://naldc.nal.usda.gov/download/20549/PDF.

Best, T. 1995. Scuirus nayaritensis. Mammalian Species, No. 492: 1-5. Accessed November 16, 2012 at http://www.science.smith.edu/departments/Biology/VHAYSSEN/msi/pdf/i0076-3519-492-01-0001.pdf.

Goldman, 2011. "Sciurus nayaritensis chiricahuae" (On-line pdf). Arizona Game and Fish Department. Accessed November 16, 2012 at http://www.gf.state.az.us/w_c/edits/documents/Sciunach.di_000.pdf.

Kneeland, M., J. Koprowski, M. Corse. 1995. Potential Predators of Chiricahua Fox Squirrels (Sciurus nayaritensis chiricahuae). The Southwestern Naturalist, Vol. 40 No. 3: 340-342. Accessed November 16, 2012 at http://www.jstor.org/discover/10.2307/30055182?uid=3739512&uid=2&uid=4&uid=3739256&sid=21101423046983.

Koprowski, J., M. Corse. 2001. Food Habits of the Chiricahua Fox squirrel (Sciurus nayaritensis chiricahuae). The Southwestern Naturalist, Vol. 46 No. 1: 62-65. Accessed November 16, 2012 at http://ag.arizona.edu/research/redsquirrel/res_pdf/Other%20Squirrel%20and%20Sky%20Island%20Publications/SWN%20Koprowski%20and%20Corse%20Food%20habits%20of%20MFS.pdf.

Lee, R., D. Hoffmeister. 1963. Status of Certain Fox Squirrels in Mexico and Arizona. Proceedings of the Biological Society of Washington, Vol. 76: 181-190. Accessed November 16, 2012 at http://biostor.org/reference/82603.

Linzey, A., J. Koprowski, L. Roth. 2008. "Sciurus nayaritensis" (On-line). The IUCN Red List of Threatened Species. Accessed November 16, 2012 at http://www.iucnredlist.org/details/20015/0.

Pasch, B., J. Koprowski. 2005. Correlates of Vulnerability in Chiricahua Fox Squirrels. USDA Forest Service Proceedings, 1: 426-428. Accessed November 16, 2012 at http://www.fs.fed.us/rm/pubs/rmrs_p036/rmrs_p036_426_428.pdf.

Pasch, B., J. Koprowski. 2006. Sex Differences in Space Use of Chiricahua Fax Squirrels. The Journal of Mammalogy, Vol. 87 No. 2: 380-386. Accessed November 16, 2012 at http://ag.arizona.edu/research/redsquirrel/res_pdf/Other%20Squirrel%20and%20Sky%20Island%20Publications/J%20Mamm%20Pasch%20and%20Koprowski%20Space%20Use%2006.pdf.

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