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)
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)
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)
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)
There is little available information on parental investment in Mexican red-bellied squirrels. Readers should refer to information on the family Sciuridae.
There is little available information on longevity in Mexican red-bellied squirrels. Readers should refer to information on the family Sciuridae.
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)
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)
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)
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)
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)
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)
In native populations, red-bellied squirrels are hunted for food.
Red-bellied squirrels sometimes cause damage to cornfields by consuming fruiting ears in Mexico. (Romero-Balderas, et al., 2006)
Red-bellied squirrels are common and the population trend is stable. (Koprowski, et al., 2013)
Alicia Byers (author), Texas A&M University, Jessica Light (author, editor), Texas A&M University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
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.
uses sound to communicate
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.
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.
uses smells or other chemicals to communicate
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.
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.
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 fruit
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
scrub forests develop in areas that experience dry seasons.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
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.
breeding takes place throughout the year
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