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Sciurus aureogasterred-bellied squirrel

By Alicia Byers and Jessica Light

Geographic Range

The range of red-bellied squirrels extends northward from southwest and central Guatemala to Guanajuato, Nayarit, and Nuevo Leon, Mexico. Two pairs were introduced to Elliott Key Island in the Florida Keys in 1938 by a resident of the island and now a population is established there. They have also been documented on Adams Key, Sands Key, and Old Rhodes Key, indicating that they may be expanding their introduced range. In one study conducted, a density of 2.47 squirrels were calculated per hectare in Elliot Key. Across the range, two subspecies have been identified: Sciurus aureogaster aureogaster, inhabiting Alta Mira, Tamaulipas, Mexico, and Sciurus aureogaster nigrescens inhabiting the rest of the geographic range. According to morphological characteristics of the baculum, red-bellied squirrels are closely related to other neotropical squirrels: Sciurus colliaei, Sciurus variegatoides, and Syntheosciurus brochus. (Brown and McGuire, 1969; Brown, 1969; Koprowski, et al., 2005; Layne, 1997; McGuire, 1975; Palmer, et al., 2014; Reid, 1997; Tilmant, 1980; Villalobos and Cervantes-reza, 2007; Wilson and Reeder, 2005)

Habitat

Red-bellied squirrels are found in a variety of forests ranging from tropical scrub and broadleaf forests of the hot lowlands to the cold and wet temperate cloud forests of oak and conifer in the highlands. They are found at up to 3,800 meters in elevation. They are most commonly found in dry woodlands and generally occur in forested habitats including thorn scrub, deciduous and evergreen forest, dry pine-oak woodland, secondary forest, and plantations. Mexican red-bellied squirrels also inhabit areas bordering agricultural and urban areas. Introduced populations in the Florida Keys are abundant in dense, subtropical hammock-forest. (Brown and McGuire, 1969; Musser, 1968; Reid, 1997)

  • Range elevation
    3,800 (high) m
    ft

Physical Description

Adult males weigh an average of 591.7 g amd adult females weigh an average of 562.5 g. Hayssen et al. 1993 report an average body mass of 505 g. Head and body length ranges from 232 to 310 mm, with tail length ranging from 215 to 284 mm. Dorsal pelage consists of salt-and-pepper coloration combined with a bright rufous belly and flank. The rufous color of the flank is spread dorsally over the area of the forelimbs and shoulder to form an hour-glass shaped marking over the back. These main pelage features are best developed and least variable in populations of the northern (Tamaulipas and eastern San Luis Potosi) and southeastern (northeastern Oaxaca, eastern Veracruz, Tabasco, and northeastern Chiapas) segments of the range. Red-bellied squirrels are one of the most variable Western Hemisphere tree squirrels in terms and color and pattern. They can have grayish upper parts that may be broken or un-patterned by nape or rump patches, a shoulder and costal patch, or combinations of those patterns. The underparts may vary from white to orange to deep chestnut. In a study area in Michoacan, squirrels were grey with white underparts. In certain segments of the range, populations exhibit melanism. In northern populations, a melanistic phase is common; about 40% of specimens sampled from Tamaulipas and eastern San Luis Potosi have high degrees of black coloration. Furthermore, introduced populations in the Florida Keys have either totally black or gray dorsal pelage with a red belly color phase in a 50% ratio. Most melanistic squirrels have a reddish tinge to the underfur on the back and rump. Reid (1997) defines four distinct color forms (although there is variation in each form). (Hayssen, 2008; Hayssen, et al., 1996; McGuire, 1975; Musser, 1968; Ramos-Lara and Cervantes, 2011; Reid, 1997)

  • Sexual Dimorphism
  • male larger
  • Range mass
    375 to 680 g
    13.22 to 23.96 oz
  • Average mass
    505 g
    17.80 oz
  • Range length
    232 to 310 mm
    9.13 to 12.20 in

Reproduction

Sciurus aureogaster exhibits year round breeding activity. Mating system is unknown, but is most likely polygynandrous as for most members of the family Sciuridae. (Brown and McGuire, 1969; Brown and McGuire, 1975; McGuire, 1975; Reid, 1997)

According to Reid (1997), Sciurus aureogaster females give birth to 2-4 offspring during the dry season across their normal distribution. For Florida populations, Sciurus aureogaster has an average of 1-2 offspring per litter and food availability appears to be the limiting factor in their reproduction. In a study by Brown and McGuire (1975), 70-90% of adult males captured in Florida exhibited signs of breeding condition year round. In the same region, lactating females varied from 50% of adult females in February and over 40% in the May-August period, to a low of 12.5% in November. In general, little is known about reproduction in this squirrel species. (Brown and McGuire, 1975; Ceballos and Galindo, 1984; McGuire, 1975; Reid, 1997)

  • Breeding interval
    Sciurus aureogaster exhibit year round breeding activity. Gestation period is unknown.
  • Breeding season
    Sciurus aureogaster exhibit year round breeding activity.
  • Range number of offspring
    1 to 4
  • Average number of offspring
    2

There is little available information on parental investment in Mexican red-bellied squirrels. Readers should refer to information on the family Sciuridae.

Lifespan/Longevity

There is little available information on longevity in Mexican red-bellied squirrels. Readers should refer to information on the family Sciuridae.

Behavior

Mexican red-bellied squirrels are diurnal with most movements starting one-half hour after sunrise until about an hour before noon, and then beginning again in the early evening hours. Even after long exposure to humans, S. aureogaster is shy and elusive. In areas where the species was introduced it rarely comes to the ground and spends most of its time on the limbs of tree canopy. In Mexico, however, squirrels can be observed using the forest floor year round, especially during the dry season. High winds, days with high ambient temperature, and cloudy and/or rainy weather inhibits normal activity. When an intruder approaches, S. aureogaster shows occasional aggressive behaviors such as emitting barks and moving its tail forward and backward rapidly. Chasing behaviors have been observed between individuals of S. aureogaster and may be involved with reproduction. The chasing behavior consists of multiple individuals chasing a single individual and producing numerous squeaking and clicking sounds over a small area of the forest.

Mexican red-bellied squirrels make leaf nests built on tree branches approximately 5-15m above ground. These leaf nests consist of a base of interwoven twigs containing an inner cup of tightly packed singular leaves and covered by a dome of interlaced leaves and small twigs. It is thought the twigs and leaves are taken from the immediate area surrounding the nest and consist of the inhabited tree species. In Mexico, S. aureogaster uses leaf nests in the following species of trees: Quercus candicans, Quercus crassipes, Quercus laurina, Quercus obtusata, Pinus pseudostrobus, Crataegus mexicana, Cornus disciflora, and Styrax ramirezii. The squirrels build nests in forks of trees or in branches of oak and pine. Individuals constructing nests bite off leafy branches 20-30cm long and interweave them into a spherical shape. During the wet season Q. candicans is used most commonly, whereas Q. laurina is most commonly used during the dry season. This preference, however, may be due to seasonal tree mast production. When available, artificial nest boxes are utilized. However, unlike their natural form, the artificial nest boxes are exposed and uncovered. In a study conducted on introduced populations in the Florida Keys, Brown and Mcguire (1975) discovered S. aureogaster uses nest boxes in tropical habitat characterized by a few natural tree hollows. Eight different tree species were used, although the West Indian Mahogany (Swietenia mahagoni) was favored and few nests were be found in poisonwood trees (Metapium toxiferum). (Brown and McGuire, 1975; McGuire, 1975; Musser, 1968; Pack, et al., 1967; Ramos-Lara and Cervantes, 2007; Ramos-Lara and Cervantes, 2011; Reid, 1997)

Home Range

Little is known about the home range sizes of Mexican red-bellied squirrels in their native range. In their introduced range in Florida, home range sizes for females are smaller than those of their male counterparts, with the average home range size for adult males is 2.3 hectares and for females it is 0.9 hectare. Home range size of breeding males are highly variable and may indicate some type of social hierarchy where certain males dominate in mating with females, while some individuals may range farther to breed with receptive females. (McGuire, 1975; Pack, et al., 1967)

Communication and Perception

Four different vocalizations have been outlined by Brown and McGuire (1975) using Sharp's (1959) terminology: 1. the call of apprehension; a low-pitched barking call when squirrels are at a safe distance but within sight of an intruder. 2. The call of danger; high-pitched barking call and a faster note. 3. The mating call; numerous rapid squeaking and clucking sounds. 4. The squeal of death; sharp, piercing high-pitched squeals. During apprehensive and danger calls, the tail is held forward over the back in an “S” position and rapidly moved forward and backward. (Brown and McGuire, 1975; McGuire and Brown, 1973; McGuire, 1975; Sharp, 1959)

Food Habits

Red-bellied squirrels are primarily frugivorous. In the lowlands of its native range, seeds and fruits of Ficus species, Cecropia species, Poulsenia armata, Brosimum alicastrum, and Astrocaryum mexicanum are commonly eaten. In the highlands, acorns and pine nuts are common food staples. In Mexico, red-bellied squirrels are observed feeding on seeds of pines (Pinus pseudostrobus), oaks (Quercus candicans, Quercus crassipes, Quercus laurina, and Quercus obtusata), and dogwoods (Cornus disciflora). In general, red-bellied squirrels feed on mangos (Mangifera indica), green figs (Ficus carica), jumbo plums (Prunus domestica), tamarind pods (Lysiloma latisiliqua), chico zapote (Manikara zapota), and corn (Zea mays). However, field observations indicate that use of food items may be based on seasonality. Red-bellied squirrels use the fruit or seeds of many different species of tropical trees and shrubs including wild mastic (Mastichodendron foetidissimum), papaya (Carica papaya), coconut (Cocos nucifera), sea grape (Coccoloba uvifera), thatch palm (Thrinax parviflora), blackbead (Pithecellobium unguis-cati), and Florida poisonwood berries (Metapium toxiferum). During the dry season of late winter and spring months, these squirrels browse on buds and twigs of mahogany, gumbo limbo (Bursera simaruba), and sea grape. When seeds are unavailable, squirrels clip branches and consume the phloem of wild mastic.

Squirrel populations in the Florida Keys exhibit food preference for gumbo limbo and the fruit of chiococca (Chiococca alba). However, the most heavily used seeds are coconut and Australian pine (Casuarina equisetifolia), which provide rich and constant food supply throughout the year along marine shorelines. (Brown and McGuire, 1969; Hall and Kelson, 1959; McGuire, 1975; Palmer, et al., 2007; Ramos-Lara and Cervantes, 2011; Reid, 1997)

  • Plant Foods
  • wood, bark, or stems
  • seeds, grains, and nuts
  • fruit

Predation

In native populations, red-bellied squirrels are hunted as food for human consumption and makes up 4.9% of the bobcat (Lynx rufus) diet. In introduced populations, there is little predation pressure. Rather, competition for food and denning sites with native fox squirrels, black rats, raccoons, frugivorous birds, owls, and other species appears to be the limiting factor on population density. (Aranda, et al., 2002; McGuire, 1975; Reid, 1997)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Red-bellied squirrels are sympatric with other fox squirrel species, including Mexican fox squirrels (Sciurus nayaritensis), Peters's squirrels (Sciurus oculatus), Allen's squirrels (Sciurus alleni), and Deppe's squirrels (Sciurus deppei), and occurs narrowly or not at all with lowland gray squirrels such as Collie's squirrels (Sciurus collaiei), variegated squirrels (Sciurus variegatoides), and Yucatan squirrels (Sciurus yucatanensis). In Elliot Key, Florida, introduced populations of red-bellied squirrels may compete with a threatened subspecies of fox squirrel, Big Cypress fox squirrels (Sciurus niger avicennia) due to an overlap in territory and shared resources. Where introduced, red-bellied squirrels can affect native fauna, such as the threatened white-crowned pigeons (Columba leucocephala). Red-bellied squirrels and white-crowned pigeons rely on the same food resources like Florida poisonberries (Metopium toxiferum) and pigeon plum berries (Coccoloba diversifolia). Mexican red-bellied squirrels may consume Florida tree snails (Liguus faciatus), a state species of special concern. Additionally, the dispersal and establishment of white oak trees can be decreased due to predation on acorns by red-bellied squirrels. Possible commensal relationships occur between red-bellied squirrels and invertebrate taxa such as ants, paper wasps, and scorpions as they were found inside man-made nest boxes with these squirrels. Screech owls (Otus asio) may use nest boxes for temporary shelter and rearing young. Red-bellied squirrels are host to a recently described species of nematode, Sciurodendrium bravohollisae, an intestinal parasite. ("Florida’s endangered species, threatened species, and species of special concern", 2004; Bancroft and Bowman, 1994; Falcon-Ordaz and Lamothe-Argumedo, 2006; McGuire, 1975; Musser, 1968; Palmer, et al., 2007; Steele, et al., 2001)

Mutualist Species
Commensal/Parasitic Species
  • Sciurodendrium bravohollisae

Economic Importance for Humans: Positive

In native populations, red-bellied squirrels are hunted for food.

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

Red-bellied squirrels sometimes cause damage to cornfields by consuming fruiting ears in Mexico. (Romero-Balderas, et al., 2006)

  • Negative Impacts
  • crop pest

Conservation Status

Red-bellied squirrels are common and the population trend is stable. (Koprowski, et al., 2013)

Contributors

Alicia Byers (author), Texas A&M University, Jessica Light (author, editor), Texas A&M University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

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.

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.

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.

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.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

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.

polygynandrous

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

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

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

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

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

urban

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

viviparous

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

year-round breeding

breeding takes place throughout the year

References

Florida Fish and Wildlife Conservation Commission. Florida’s endangered species, threatened species, and species of special concern. Gainesville, Tallahassee: Florida Fish and Wildlife Conservation Commission. 2004. Accessed August 20, 2014 at http://www.colliergov.net/Modules/ShowDocument.aspx?documentid=1052.

Aranda, M., O. Rosas, J. Rios, N. Garcia. 2002. Comparative feeding analysis of the bobcat (Lynx rufus) in two different localities in Mexico. Acta Zoologica Mexicana Nueva Serie, 87: 99-109.

Bancroft, G., R. Bowman. 1994. Temporal patterns in diet of nestling white-crowned pigeons: implications for conservation of frugivorous columbids. American Ornithologists Union, 111/4: 844-852.

Brown, L. 1969. Exotic squirrel in Florida. Florida Wildlife, 23: 4-5.

Brown, L., R. McGuire. 1975. Field ecology of the exotic Mexican red-bellied squirrel in Florida. Journal of Mammalogy, 56(2): 405-419.

Brown, L., R. McGuire. 1969. Status of the red-bellied squirrel (Sciurus aureogaster) in the Florida Keys. American Midland Naturalist, 82/2: 629-630.

Ceballos, G., C. Galindo. 1984. Mamíferos silvestres de la cuenca de México. Universidad Nacional Autónoma de México, 12: 299.

Emmons, L. 1990. Neotropical rain forest mammals: a field guide. Chicago: University of Chicago Press.

Falcon-Ordaz, J., M. Lamothe-Argumedo. 2006. A new species of Sciurodendrium (Nematoda: Haligmonellidae) in Sciurus aureogaster from Morelos, Mexico. Journal of Parasitology, 92/3: 600-605.

Hall, E., K. Kelson. 1959. The Mammals of North America. New York: The Renolds Press Co.

Hayssen, V. 2008. Reproductive effort in squirrels: ecological, phylogeneitc, allometric, and latitudinal patterns. Journal of Mammalogy, 89(3): 582-606.

Hayssen, V., A. Van Tienhoven, A. Van Tienhoven. 1996. Asdell's patterns of mammalian reproduction: a compendium of species-specific data. Ithaca, New York: Cornell University Press.

Koprowski, J., G. Kellison, S. Moneysmith. 2005. Status of red-bellied squirrels (Sciurus aureogaster) introduced to Elliott Key, Florida. Florida Field Naturalist, 33(4): 128-129.

Koprowski, J., L. Roth, F. Reid, N. Woodman, R. Timm, L. Emmons. 2013. "Sciurus aureogaster" (On-line). IUCN Redlist. Accessed April 20, 2014 at www.iucnredlist.org.

Layne, J. 1997. Nonindigenous mammals. Pp. 157-186 in D Simberloff, D Schmitz, Brown, T., eds. Strangers in Paradise: impact and management of nonindigenous species in Florida. Washington, D.C.: Island Press.

McGuire, R. 1975. Field ecology of the exotic Mexican Red-Bellied Squirrel in Florida. Journal of Mammalogy, 56: 405-419.

McGuire, R. 1969. Status of the Red-Bellied Squirrel (Sciurus aureogaster) in the Florida Keys. Journal of Mammalogy, 82: 629-630.

McGuire, R., L. Brown. 1973. Coconut feeding behavior of the red-bellied squirrel on Elliot Key, Dade Co., Florida. American Midland Naturalist, 89: 498.

Musser, G. 1968. A systematic study of the Mexican and Guatemalan gray squirrel, Sciurus aureogaster F. Cuvier (Rodentia:Sciuridae). Museum of Zoology, 137: 5-189.

Pack, J., H. Mosby, P. Siegel. 1967. Influence of social hierarchy on gray squirrel behavior. Journal of Wildlfie Management, 31: 720-728.

Palmer, G., J. Koprowski, A. Pernas. 2014. Distribution and spread of an introduced insular population of red-bellied squirrels (Sciurus aureogaster) in Florida. Mammalia, 78(1): 67-73.

Palmer, G., J. Koprowski, A. Pernas. 2013. Nest tree and site selection of an introduced population of red-bellied squirrels (Sciurus aureogaster). Journal of Mammalogy, 94(6): 1274-1281.

Palmer, G., J. Koprowski, T. Pernas. 2007. Tree squirrels as invasive species: conservation and management implications. Managing Vertebrate Invasive Species, 36: 273-282.

Pernas, A., D. Clark. 2011. gray sqA summary of the current progress toward eradication of the Mexican uirrel (Sciurus aureogaster F. Cuvier, 1829) from Biscayne National Park, Florida, USA. Pp. 222-224 in C Veitch, M Clout, D Towns, eds. Island invasives: eradication and management. Gland, Switzerland: IUCN.

Ramos-Lara, N., F. Cervantes. 2011. Ecology of Mexican red-bellied squirrel (Sciurus aureogaster) in Michoacan, Mexico. Southwestern Association of Naturalists, 56/3: 400-403.

Ramos-Lara, N., F. Cervantes. 2007. Nest-site selection by the Mexican red-bellied squirrel (Sciurus aureogaster) in Michoacan, Mexico. Journal of Mammalogy, 88/2: 495-501.

Reid, F. 1997. "Rodents" A field guide to the mammals of Central America and Southeast Mexico. New York: Oxford University Press.

Romero-Balderas, K., E. Naranjo, H. Morales, R. Nigh. 2006. Damages caused by wild vertebrate species in corn crops at the Lacandon Forest, Chiapas, Mexico. Interciencia, 31/4: 276-283.

Sharp, W. 1959. A commentary on the behavior of free running gray squirrels. Proceedings of the Southeastern Association Game and Fish Commissioners, 13: 382-387.

Steele, M., G. Turner, P. Smallwood, J. Wolff, J. Radillo. 2001. Cache management by small mammals: experimental evidence for the significance of acorn-embryo excision. Journal of Mammalogy, 82/1: 35-42.

Tilmant, T. 1980. Investigations of rodent damage to the thatch palms Thrinax morrisii and Thrinax radiata on Elliot Key, Biscayne National Park, Florida. South Florida Research Center, Everglades National Park.

Villalobos, F., F. Cervantes-reza. 2007. Phylogenetic relationships of Mesoamerican species of genus Sciurus (Rodentia: Sciuridae). Zootaxa, 1525: 31-40.

Wilson, D., M. Reeder. 2005. Mammal Species of the World. A Taxonomic and Geographic Reference. Baltimore, MD: Johns Hopkins University Press.

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