Neotoma albigula
Turner Island woodrat
(Also: white-throated woodrat)

Neotoma albigula occupies a wide range of habitats in the southwestern United States and northern Mexico. The northern extent of its range includes the Four Corners region and the southernmost tip of Nevada. It can also be found as far west as southeastern California and as far east as central Texas. It is distributed widely throughout New Mexico and Arizona and through most of northern Mexico. (Cockrum, 1982; Macedo and Mares, 1988; Zeveloff, 1988)

Neotoma albigula appears in a wide range of habitats including forest edges, scrubland forests, and low deserts, and can be found from 2135 m to 76 m in elevation. It occasionally builds dens in the caves of rocky hills, but more commonly prefers areas of extensive cholla and prickly pear cactus. Using cacti and other large desert plants as an anchor, N. albigula builds an extensive home using pieces of cacti, cow chips, sticks, bones, and any other found items, including garbage left by humans. It is known for its large and complex shelters. Averaging 8 feet in diameter and 2 to 3 feet in height, its shelters contain several chambers and underground tunnels which are used to escape predators. Each shelter also includes a small underground nest that serves as a retreat from daytime heat and as a place for females to raise their young. The size of the nest averages about 8 inches in diameter. It consists of soft materials such as grasses or shredded fibers. The average density of N. albigula shelters in heavily populated areas is between 5 to 15 per acre, but densities vary depending on resource availability. Neotoma albigula is a solitary species and houses are never cohabited by adults. (Brown, 1968; Hoffmeister, 1986; Macedo and Mares, 1988; Olsen, 1971)

In general, Neotoma albigula has a medium-sized body with brownish gray fur covering dorsum. The venter is white or light gray with a white throat. The tail is shorter than the length of the body, is bi-colored and is covered in moderately long hair. The ears are large and hairless. Average mass is 197 g and average head-body length is 328 mm; however, body size varies depending on climate, with larger specimens found in colder regions and smaller specimens found in warmer regions. Black color-morphs of N. albigula occur on lava beds in Texas and New Mexico. The species is further divided into 13 subspecies that occupy overlapping ranges throughout the southwestern United States and northern Mexico. Subspecies are distinguished primarily by morphometric characteristics (e.g., body size). Average basal metabolic rate for this species is 36000 cm^3 oxygen/hour. Sexual dimorphism has not been documented in N. albigula. (Cockrum, 1982; Macedo and Mares, 1988; Zeveloff, 1988)

Mating the only time that Neotoma albigula engages in social behavior with adults conspecifics. Foot thumping often precedes copulation, although the purpose is unknown. During copulation, males and females have limited tactile contact and males do not clasp the female. The average copulatory lock lasts 30.1 seconds. It is hypothesized that this short lock has evolved to minimize predation risk as copulation can create vulnerability to attack. Mate selection behavior is not well understood. Neotoma albigula is promiscuous and no bonding occurs between mates after copulation. (Macedo and Mares, 1988)

Reports on the breeding season of Neotoma albigula vary greatly. Some observations suggest year-round breeding, while others identify a period between January and September as breeding season. This discrepancy may be a result of differences in breeding seasons among the different regions occupied and/or subspecies. However, all sources agree that breeding slows during the hottest months of the year and that the majority of breeding takes place between January and June. Neotoma albigula can produce multiple litters per season, and females are sometimes found with offspring of two different ages in their dens. Average gestation lasts 38 days, however, gestation periods short as 30 days have been recorded. Litters range from 1 to 4 offspring, with an average of 2 offspring per litter. Average birth mass is 10.9 grams. Weaning occurs between 62 and 72 days, at which point offspring have already begun practicing shelter construction and consuming cacti, berries, and vegetation. In the wild, N. albigula reaches sexual maturity at around 180 days. In captivity, instances of reaching sexual maturity as young as 80 days in females and 101 days in males have been documented. (Macedo and Mares, 1988)

Male N. albigula play no role in rearing the offspring. Little is known about pre-conception preparation for reproduction by the female, although den construction could be considered part of her investment. As is the case for all mammals, the mother uses her body to protect the offspring in utero. After birth, a female lactates and feeds the offspring her milk for 62 to 72 days. She cares for and protects her young for approximately 6 months until they have reached maturity and disperse to build their own houses. A female can have more than one litter residing in her home at one time, but only one litter nurses at a time. Some subspecies are known to wean and mature earlier than average, reducing parental investment. (Olsen, 1971; Prakash and Ghosh, 1975)

Little is known on the lifespan of Neotoma albigula. The few existing data suggests that members of this species can live between 3 and 5 years. Longest known lifespan in the wild is 6 years. (Zeng and Brown, 1989)

Neotoma albigula is primarily nocturnal, but some observors have reported daytime activity within the den. It remains active year round. As a solitary species, it has very limited social interactions; these occur between adults only during copulation. The only other social interaction experienced by N. albigula is that between a mother and her offspring. Foot thumping is thought to be a form of communication between conspecifics in N. albigula and has been observed prior to copulation and as a reaction to predatory threats. Offspring as young at 26 days old have been observed to participate in foot thumping as a reaction to predatory stimuli. (Cockrum, 1982; Macedo and Mares, 1988; Olsen, 1971)

Nest construction involves collecting many different items. Neotoma albigula constructs large nests that integrate cacti, sticks, animal bones, cow chips and man-made materials. Members of this species appear to have a particular affinity for collecting man-made objects for incorporation into the nest. See Habitat section for additional information. (Macedo and Mares, 1988)

Home ranges of Neotoma albigula average about 486 m^2 and nest densities average 5 to 15 every 4,000 m^2. Nests are separated by an average distance of 12 meters, causing many home ranges to overlap, which does not appear to be a source of agonistic behavior among residents. Territorial behavior near the nest has been observed. (Macedo and Mares, 1988; Olsen, 1971)

White-throated woodrats use scent to communicate with conspecifics. Males have specialized midventral glands that they use to scent mark selected locations. In females, this gland is poorly developed. Pheromones are used in social situations involving courtship, sexual, agonistic, hierarchical, and possibly territorial interactions. Pheromones present in feces are used to determine the sex of den occupants, thereby avoiding agonistic encounters between males. White-throated woodrats rely upon scent and visual cues to warn them of danger from predators. Altricial infants with unopened eyes cannot distinguish a predator by scent alone. (Macedo and Mares, 1988)

In desert habitats, Neotoma albigula feeds primarily on cholla and prickly pear cactus. Neotoma albigula is not an obligate drinker and acquires most of its water from cactus. Some observations estimate that the diet of N. albigula consists of up to 44% cacti. During periods of exceptionally high temperatures, N. albigula can eat upwards of 60% of its body mass in cacti per day. While this species prefers cacti, it is considered a generalist herbivore. Other important food items includes the beans and bark of mesquite plants, juniper branches and berries, various flowers, and yucca leaves. Neotoma albigula has also been observed consuming insects, small reptiles and mice, however, such observations are uncommon. Neotoma albigula is known to store food throughout its large shelter. (Macedo and Mares, 1988; Olsen, 1971; Zeng and Brown, 1989; Zeveloff, 1988)

Predators of Neotoma albigula include a number of mustelids such as weasels, skunks, and badgers. Additional mammalian predators include racoons, red fox, gray fox, bobcats, coyotes, and ringtails. Other important predators of N. albigula include snakes and Great-horned Owls (Davis, 1960; Hoffmeister, 1986; Macedo and Mares, 1988; Olsen, 1971; Prakash and Ghosh, 1975)

Altricial young are unable to identify predators by smell alone and treat predators as inanimate objects. Once their eyes are open, visual clues play an important role in predator detection for individuals as young as 26 days. In predatory experiments, the reaction of Neotoma albigula to predatory stimuli occurs in three steps: awareness of threat, foot thumping and increased agitation, and fast and random direction running. Structural adaptations to predation are thought to have lead to extensive tunnels and chambers in and around the habitation structures of N. albigula. Tunnels appear to function as a means of escape when faced with a potential threat in or near the nest. A large proportion of N. albigula's shelter is constructed from pieces of cacti. These spiny additions act as a deterrent for predators, without inhibiting the mobility of N. albigula. Nocturnal behavior likely reduces risk of predation. By remaining inside during the day, N. albigula avoids many predators including many bird species and other diurnal predators. The coloration of N. albigula likely helps camouflage them from potential predators as well. (Davis, 1960; Hoffmeister, 1986; Macedo and Mares, 1988; Olsen, 1971; Prakash and Ghosh, 1975)

The herbivorous diet of Neotoma albigula consists primarily of cacti, their fruit and other desert vegetation. Its diet can alter the vegetation profile of the local area and may facilitate seed dispersal. Shelter construction and fecal distribution can cause an increase in the amount of soluble salts, bicarbonates, and nitrates in the soil. Once abandoned, shelters can be inhabited by a range of species including other woodrats, desert reptiles , and numerous species of rodents. Parasites specific to N. albigula have not been documented. (Macedo and Mares, 1988; Prakash and Ghosh, 1975)

There are no known positive effects of Neotoma albigula on humans, however, there have been rare reports of humans consuming N. albigula. (Macedo and Mares, 1988)

Neotoma albigula causes damage to cabins and summer homes where it may occasionally nest in the absence of humans. Damage to furniture and other items that woodrats incorporate into nests is not uncommon, and significant amounts of fecal waste have been left in absent residences. Additionally, N. albigula has been known to raid food stores that are poorly sealed. (Macedo and Mares, 1988; Zeveloff, 1988)

Neotoma albigula is widespread and abundant throughout its geographic range. As a result, this species is classified as "least concern" on the IUCN's Red List of Threatened Species.

Another common term for the white-throated woodrat is "packrat". This term refers to its tendency to cache man-made objects.