In general, white-throated woodrats occupy desert grasslands [19], semiarid shrublands [48,58,88,99,134], saguaro (Carnegiea gigantea) cactus communities [75], pinyon-juniper (Pinus-Juniperus spp.) woodlands, interior ponderosa pine (P. ponderosa var. scopulorum) forests, and Madrean evergreen woodland (Pinus spp.-Quercus spp.) [88].
Colorado:
Utah:
Arizona:
California:
New Mexico:
Texas:
Mexico:
Queretaro, Mexico:
White-throated woodrats must rely on self-constructed, ground-level shelter to lower the energetic costs of thermoregulation in extreme environments [21,94,97,98,131]. White-throated woodrats typically use 2 types of shelter: houses, constructed at the base of plants, and dens in rock crevices [45,83,97,98,131]. Other shelter types include holes and crevices in cutbanks along washes [104,132], subterranean burrows of other animals [21,104,108,142], piles of coarse woody debris, and human habitations and structures [132]. Houses and dens are often maintained by successive generations of white-throated woodrats [97,98].
Houses are built by white-throated woodrats at the base of trees, shrubs, and cacti [83,85,97,98,131,134] or in piles of coarse woody debris [97,116]. White-throated woodrats prefer to construct houses at the bases of plants that provide both adequate shelter and food. Houses are constructed of various materials (see Building materials) and are typically 3 to 10 feet (1-3 m) in diameter and up to 3 feet tall [132]. Dens function as houses but are located in rock crevices, rock fissures, and under boulder piles [21,33,83,85,97,98,108,131,132,134].
Houses and dens enclose a system of runways and chambers, including the white-throated woodrat's nest [97,98]. The nest averages 8 inches (20 cm) in diameter and is composed of soft, fine material including grass, shredded prickly-pear fibers, or juniper bark [131,132].
Building materials: White-throated woodrats use locally available building materials to construct houses [83,94]. In wooded areas, white-throated woodrats use sticks and other debris, and in deserts, parts of cacti, catclaw acacia, mesquite, and yucca are typically used [83,131]. Cactus parts are preferred building materials; preference for cacti is so strong that white-throated woodrat houses may not contain a proportionally representative sample of the surrounding plant community [22,131]. Other building materials used by white-throated woodrats across their range include feces, bones, and human objects [22,33,94,97,131,132]. Of 100 white-throated woodrat houses found on the Santa Rita Experimental Range, 75 different items were used for construction. The most commonly used building materials included mesquite, catclaw acacia, paloverde, desert ironwood (Olneya tesota), and creosotebush twigs; cholla joints and fruits; portions of prickly-pear where it was abundant; and juniper, pinyon pine, and oak twigs where they were abundant. Other items included horse, cow, and coyote dung, animal bones, stones, and human-discarded materials [131].
Building materials are gathered near the white-throated woodrat's shelter. At McDowell Mountain Regional Park, Arizona, white-throated woodrats gathered 30% of house building materials within 33 feet (10 m) from their shelter. Houses and dens are altered and refurbished during the year using new and old building materials [94].
In Guadalupe Mountains National Park and the Lower Sonoran zone of Arizona, use of building materials depended on availability [33,132]. Juniper leaves and berries were used most often in a pinyon-juniper woodland, and mesquite leaves and pods and Christmas cactus (Cylindropuntia leptocaulis) joints were used most often in a desert scrub habitat [33]. In the Lower Sonoran desert of Arizona, white-throated woodrats favored some plants because of their structural and food values and favored other plants due to their availability. When available, cholla was used most often for building material due to its structural and food values. Mesquite sticks were used frequently. Although mesquite was seldom used for food, mesquite sticks were abundant at the base of plants so they were readily available. White bursage (Ambrosia dumosa) was very abundant and used for building material, even though plants were too small to shelter a white-throated woodrat den [132].
Relationship of white-throated woodrat den locations and house materials of 100 houses in the Lower Sonoran desert, Arizona [132] Cover above den No. dens located under No. occurrences as building material Plant part used Cholla 21 73 Chiefly cholla cactus joints Mesquite 15 40 Sticks Catclaw acacia 21 26 Sticks Prickly-pear 19 22 Pads or skeletons White bursage 0 16 Small bushes Desert hackberry (Celtis pallida) 6 9 Sticks Creosotebush 7 7 Sticks Ephedra spp. 3 3 Stems Yucca 4 4 Leaves, pieces of stem Paloverde 0 2 Sticks Saguaro 1 2 Saguaro "pearls"*, pieces of bark Desert ironwood 1 1 Sticks In the open 2 0 ---- *The definition of "pearls" was not given in the articleShelter sites: Cover near the ground is an important criterion for white-throated woodrat shelter sites. In northern portions of their range, white-throated woodrats tend to construct houses at the bases of trees [21,33,128,132]; in southern portions of their range, white-throated woodrats tend to construct houses at the bases of shrub-trees, shrubs [33,90,115,121,132], or cacti [22,33,94,132]. When available, rocks are preferred by white-throated woodrats for shelter because they provide more protection from variations in ambient temperature than the base of plants [97,98,131].
Plants: Although any tree, shrub, or cactus may be used by white-throated woodrats for shelter sites [132], the most commonly used plants are discussed below.
Juniper: White-throated woodrats construct houses at the base of live and dead fallen juniper trees in pinyon-juniper woodlands in Arizona [132], New Mexico [128], Utah [21], and Texas [33]. The base of pinyons are occasionally used [132].
Mesquite: Mesquite is often favored by white-throated woodrats for shelter in habitat dominated by mesquite in New Mexico [90], Arizona [21,90], California [115], and Texas [33]. In habitat dominated by mesquite and creosotebush in San Diego County, California, all white-throated woodrat houses were located at the bases of honey mesquite. Twenty to 26-foot tall (6-8 m) honey mesquite were preferred over 3 to 10 foot (1-3 m) tall honey mesquite, probably because they provided more shelter and abundant, accessible food [115]. An exception in habitat dominated by mesquite occurred on the Santa Cruz river bottom near Tucson, Arizona, where white-throated woodrat houses were also built under netleaf hackberry, American black elderberry (Sambucus nigra), skunkbush sumac (Rhus trilobata), bear grass (Nolina spp.), or saguaro [132].
Yucca: In habitats where yucca are abundant white-throated woodrats use the base of yucca for shelter sites. On the Jornada Experiment Range in New Mexico, and the Black Gap Wildlife Management Refuge in Trans-Pecos Texas , white-throated woodrats built houses at the bases and fallen trunks of yucca [121,132]. Soaptree yucca was used by white-throated woodrats in the lower Sonoran zone of the Lordsburg Plains in New Mexico and the San Simon Valley in Arizona [90].
Cholla and prickly-pear: Cholla and prickly-pear are often used by white-throated woodrats for cover because they provide excellent protection from predators, as well as food and water [22,90,94,132,134]. One of the factors in white-throated woodrat shelter-site selection in McDowell Mountain Regional Park was presence of teddybear cholla [94]. In the Cholla Garden in Joshua Tree National Monument, white-throated woodrats depended on stands of jumping cholla (Cylindropuntia fulgida) for cover [22], and in the Lower Sonoran zone of Arizona, most white-throated woodrat dens were found at the bases of cholla and prickly-pear [90,132].
In Guadalupe Mountains National Park, white-throated woodrat distribution may be limited more by the presence of Mexican woodrats (N. mexicana) and the southern plains woodrat (N. micropus) than by habitat limitations. In areas not inhabited by Mexican woodrats and southern plains woodrats, the white-throated woodrat constructed houses at bases of prickly-pears. In areas where white-throated woodrats and southern plains woodrats lived in close proximity, white-throated woodrat constructed houses under honey mesquite [33].
Other vegetation: In the Lower Sonoran zone of Arizona and New Mexico, white-throated woodrats commonly used the bases of catclaw acacia for shelter [90,132].
White-throated woodrats selected multiple-stemmed plants over single-stemmed plants and a dense, low canopy over a tall, thin canopy in habitat dominated by triangle bursage in Organ Pipe National Monument in Arizona and New Mexico. White-throated woodrats selected house sites in reverse order of plant abundance: yellow paloverde 18.1 plants/ha, 6 houses; desert ironwood, 7.6 plants/ha, 14 houses; and organ pipe cactus, 5.0 plants/ha, 21 houses. Yellow paloverde was probably selected for shelter least often because it is a single-stemmed tree with a tall canopy; organpipe cactus (Stenocereus thurberi) was probably selected most often because it is a multiple-stemmed plant with many cylindrical stems branching near the ground from a central trunk, providing more cover [97,98].
Rock: In juniper woodlands in the high desert of southeastern Utah, white-throated woodrats occasionally denned under boulder crevices at the bases of vertical cliffs [21]. In habitat dominated by brittle bush in Saguaro National Monument, all 103 white-throated woodrat dens were located within jumbles of rocks or under boulders. Ninety-one dens were located under boulders >7 feet (2 m) in diameter, and 12 dens were located under boulders <7 feet in diameter [97,98].
Other shelter sites: White-throated woodrats occasionally use river banks [104], subterranean areas [104,142], or caves [131] for shelter. In habitat dominated by honey mesquite and creosotebush at Carrizo Creek in San Diego County, white-throated woodrats sought cover either in river banks or subterranean burrows that were probably excavated by kangaroo rats (Dipodomys spp.). Lack of stick houses may have been due to a harsh summer climate, ease of burrowing in loose sand, scarcity of building materials, or adequate overhead protection by honey mesquite. River banks were 6 to 15 feet (2-5 m) high, and burrows were excavated at various heights from the bottom. Hole diameter was 3.5 to 7 inches (8.9-18 cm). White-throated woodrats also dwelled in subterranean burrows with as many as 8 openings, covered with a few small twigs, at the bases of honey mesquite [104]. In a similar habitat type in the Mesilla Valley of New Mexico, white-throated woodrats denned in sand dunes created by banner-tailed kangaroo rats (D. spectabilis) around honey mesquite [142].
White-throated woodrats appear to be susceptible to fire-related death [67,73,85,103,118]. Most woodrat species are reluctant to vacate their houses when threatened by fire [73,103]. Komarek [73] noted that some white-throated woodrats fled during a fire, but many appeared to be panic-stricken and remained immobile until the flames reached them or they were set afire. In a prescribed fire study conducted by Simons [118] in Arizona, white-throated woodrat survival dropped sharply during fire.
Because many white-throated woodrats construct houses at the bases of vegetation (see Cover), they may be more vulnerable to direct mortality than small mammals that occupy subterranean habitats [67,85,103,118]. Fires that occur during spring may be harmful to young white-throated woodrats due to limited mobility [81].
The ranges of the white-throated woodrat and its subspecies are from the southeastern corners of Nevada and California across southern Utah and all of Arizona to southwestern Colorado, across west Texas and south to central Mexico [44,60,135]. NatureServe provides a distributional map of the white-throated woodrat and 2 subspecies.
The distributions of white-throated woodrats are described below [58]. The distribution of Neotoma albigula seri was not described in the available literature.
N. a. albigula: Northern New Mexico and northeastern Arizona south along the east side of the Sierra Madre Oriental, to southern Coahuila, Mexico. Also central Texas to western Arizona, and south along the western side of the Sierra Madre Occidental to central Sonora [60,132]
N. a. brevicauda: Utah and Colorado [49]
N. a. durangae: Southwestern Chihuahua [60,132] and central Durango, Mexico [8,132]
N. a. laplataensis: Utah, Colorado, and Arizona [60]
N. a. latifrons: Michoacán, Mexico [58,59]
N. a. leucodon: East of the Rio Grande in New Mexico, Texas, and Oklahoma [44]; Durango, Zacatecas, San Luis PotosÃ, Guanajuato, Jalisco, Aguascalientes, Querétaro, Hidalgo [58,59], and southeastern Coahuila, Mexico [132]
N. a. mearnsi: Arizona
N. a. melanura: Central Sonora [60,132], Chihuahua [60], and Sinaloa, Mexico [72]
N. a. melas: New Mexico
N. a. robusta: Texas [58]
N. a. sheldoni: Northeastern Sonora, Mexico [58,132]
N. a. subsolana: Coahuila [60], Tamaulipas, Nuevo León, and Coahuila, Mexico [3]
N. a. venusta: Colorado River valley in western Arizona [132] south to Sonora and Baja California, Mexico
N. a. warreni: Colorado, Oklahoma [58,60], northeastern New Mexico [58,132], and Texas [60]
Specific fire management recommendations for the white-throated woodrat are few. White-throated woodrats commonly occur in xeric habitats [21,37,90,94,131,132,137] where fire frequency is generally low [70,87,100]. Low-severity fire may not greatly impact white-throated woodrats; however, moderate- to high-severity fires can damage or kill fire-sensitive trees, shrubs, and cacti that are required for shelter, food, and water [9,30,43,66,70,79,92,126,139,141]. In several studies, white-throated woodrat numbers decreased following wildfire [85,89] and prescribed fire [12,118], and postfire recovery was slow [118].
Desert vegetation appears to be most susceptible to burning during late spring and early summer, which is the hottest and driest time of the year in Arizona [26]. Because young white-throated woodrats are born during this time [22], they may be easily killed by burning.
Establishment of nonnative grasses, primarily red brome and buffelgrass, is altering FIRE REGIMES and habitats in the Sonoran Desert. Nonnative grasses provide abundant and continuous fuels, resulting in increased fire frequency. Since these species can increase in dominance following fire, repeated burning can convert native-dominated white-throated woodrat habitat into nonnative grassland. These grasslands are, in turn, likely to burn repeatedly. Thus, a grass/fire cycle is established. Reviews of the impacts of nonnative grasses on FIRE REGIMES and community composition, including descriptions of the nonnative grass/fire cycle, are available in these sources: [15,17,36,47,107]. Climate change may also negatively affect the white-throated woodrat if droughts become more frequent or severe, or if precipitation increases and results in the spread of nonnative grasses [10].
White-throated woodrats are less common in southwestern ponderosa pine forests and pinyon-juniper woodlands than in desert habitats. In southwestern ponderosa pine forests where fire has not occurred in decades, Harrington and Sackett [63] recommend prescribed burning in early spring or fall when temperatures and humidities are moderate, but burning during spring may harm young white-throated woodrats [81]. White-throated woodrats prefer low tree canopy cover and coarse woody debris [1,14,45,116] and may potentially benefit from thinning if coarse woody debris is left in place, though field observations have not been reported in regard to this possibility. Prescribed burning may also benefit white-throated woodrats by opening the canopy. Protection of shrubs, coarse woody debris, and litter may be needed during prescribed burning due to their importance to the white-throated woodrat.
White-throated woodrats are opportunistic [56] and primarily herbivorous [31]. Their diet consists of seeds [56,83], fruits [134], green portions of plants [32,83,134,137], flowers [56], small amounts of grass [90,134], and occasionally beetles (Coleoptera), ants (Hymenoptera) [83,132,134], and reptiles [132]. Some of the most commonly consumed plants across the white-throated woodrat's range include mesquite flowers, leaves, seeds, and bark [83,90,104,115,132,134,137], cacti flowers, stems, and fruits [83,90,98,132], and yucca leaves [39,137].
Foods eaten by white-throated woodrats depend on availability. In Great Basin scrub desert and juniper woodlands in northern Arizona (Coconino County) white-throated woodrat diet was 29% yucca, 24% juniper, 7% rabbitbrush (Chrysothamnus spp.), 6% sumac, 5% Apache-plume (Fallugia spp.), 4% sagebrush (Artemisia spp.), 4% saltbush, and 3% ephedra (Ephedra spp.) [39]. In the Lower Sonoran zone of southern Arizona (Santa Rita Experimental Range), cacti and mesquite were the primary foods eaten. For a complete list of foods eaten by white-throated woodrats in the Santa Rita Experimental Range, see Vorhies and Taylor [132]. In the southern Great Basin, Navajo yucca (Y. baileyi) is an important food for the white-throated woodrat [39].
White-throated woodrats require large amounts of water obtained through various xerophytic plants [39,98,131,132,134], especially cacti [98]. In Organ Pipe National Monument, white-throated woodrats relied heavily on teddybear cholla, buckhorn cholla (Cylindropuntia acanthocarpa), jumping cholla, and goatnut (Simmondsia spp.) for water [98]. In Coconino County, white-throated woodrats obtained water from evergreen species (Ephedra spp., Yucca spp., and Juniperus spp.), which maintained a high year-round water content [39].
Seasonal dietary changes: The white-throated woodrat diet varies seasonally. In Coconino County, white-throated woodrats ate a variety of plants, including deciduous shrubs, during warm, wet months when plant moisture was high. During cool, dry months, their diet was restricted largely to evergreen plants. Regardless of season, white-throated woodrats preferred to eat evergreen species [39]. At Carrizo Creek, honey mesquite leaves, flowers, and fruits were the main foods eaten from the end of March until the end of summer. After honey mesquite lost its leaves, white-throated woodrats subsisted on stored beans, bark, and stems [115].
Food storage: Some white-throated woodrats store food in their houses [131,132,134]. Of 30 white-throated woodrat dens found in Doña Ana County, New Mexico, 77% contained stored food. The average weight of stored food was 2.2 pounds (1.0 kg)/den (range 0.1 to 9.3 pounds (0.05-4.2 kg)/den)). Most stored food consisted of mesquite beans and cacti and forb seeds [137]. In general, white-throated woodrats collect food within a 98- to 164-foot (30-50 m) radius of their dens [131].
White-throated woodrats occur in a range of habitats, including ponderosa pine forests and pinyon-juniper woodlands, but are most commonly associated with desert shrublands in the Sonoran and Chihuahuan deserts (see Preferred Habitat and Cover requirements). HABITAT RELATED FIRE EFFECTS in these desert plant communities are the focus of this section.
Presettlement FIRE REGIMES: Deserts typically burn less frequently than most ecosystems because little fuel is produced in the arid desert climate. The less fuel that is produced, the less frequent and less severe are any fires that may occur [70]. Desert shrub communities and desert grasslands had somewhat different historical fire regimes.
Presettlement FIRE REGIMES in desert shrub communities have been characterized by relatively infrequent, stand-replacement fires with return intervals in the range of 35 years to several centuries [41,42,100]. The dominance of long-lived, fire sensitive species in the Sonoran Desert suggests long fire-free periods [47,70]. Severe lightning storms, high air temperatures, and low relative humidity in the summer months create favorable conditions for fire in desert ecosystems [70]; however, fuels were historically sufficient to carry fire only after periods of above-average precipitation [70,87,111]. Although several perennial grasses occur in these communities, they are usually too sparse to provide a reliable fuel base or continuity of cover for carrying fire [70]. In years of exceptional rainfall, extensive areas of the Sonoran Desert may have supported sufficient annual grasses or forbs to carry fire [70,111]. The Chihuahuan Desert is somewhat similar to the Sonoran with regard to the rarity of fire. However, a greater proportion of low-growing shrubs and perennial grasses may have given the occasional fires a greater opportunity to spread, resulting in fire-return intervals at the lower end of the range in areas with a substantial grass component [41,42]. Although fire frequency and severity may be relatively low in desert shrublands, their effect on these ecosystems may be extreme [70,87].
Areas that support desert grassland may have a history of more frequent fire than desert shrublands, resulting in a grass subclimax [70]. Most fires probably occurred in summer, when thunderstorms moved into the region after the extended hot, dry period in May and June. Summer fires were particularly important for sustaining grasses at the expense of woody plants. Most perennial plants, including grasses, are susceptible to mortality from summer fires, but woody plants are especially susceptible to summer fires (review by [107]). Contemporary fires in desert shrubland often occur at the ecotone between desert shrublands and desert grasslands, particularly during years of above-average precipitation [70,87,111]. Boundaries between desert shrubland and desert grassland have probably shifted during the past century as grazing and fire exclusion have favored native woody plant dominance [70,72,113].
Altered FIRE REGIMES: Increased fire frequencies have been reported in recent decades in many parts of the desert Southwest (e.g., [28,110]). Human settlement and land management activities and associated vegetation changes during the past century have contributed to changes in these FIRE REGIMES. Establishment, spread, and dominance of nonnative grasses, especially in the Sonoran Desert, have altered fuel characteristics of some invaded sites such that fires occur more frequently and cover larger areas. Nonnative grasses provide a large biomass of continuous fine fuels that are more likely to ignite and carry fire than fuels of native species, especially following years of above-average precipitation [15,16,47,111]. Contemporary fires (during the past 2 decades) in the Sonoran Desert burn in May and June and are fueled to a great extent by nonnative annual grasses including red brome (Bromus rubens), Mediterranean grass (Schismus spp.), and cheatgrass (Bromus tectorum) [47]. More recently, buffelgrass, a shrubby nonnative perennial grass that grows in dense monocultures, has spread in part of the Sonoran Desert and fueld large, intense, severe fires. Buffelgrass accumulates large amounts of coarse, dense litter as it grows and senesces each year, and it burns easily, even when green. Unlike annual grasses, it is therefore not dependent on years of high precipitation to create large amounts of continuous, fine fuels. Buffelgrass fueled a fire so severe north of Hermosillo, Mexico, that the soil was scorched, the bedrock cracked, and dominant trees in the foothills thornscrub were not only killed but completely incinerated [46]. See the FEIS reviews of red brome and buffelgrass for more information on their effects on fuel characteristics and FIRE REGIMES.
While lightning was the dominant ignition source historically, in recent decades human-caused ignitions, such as those started by campfires, fireworks, and vehicle use, account for the majority of fires in the desert Southwest. For example, human-ignited fires accounted for almost 66% of fires in the Tonto National Forest of Arizona from 1955 to 1983, with a significant (P<0.05) increase in number of human-started fires during the study period [114].
Effects of fire on native vegetation: Fires fueled by nonnative grasses can be very severe, especially in terms of their impact on dominant, native, fire-sensitive plants [47,70,87,112]. In the Sonoran Desert, fire is clearly detrimental to upland desertscrub vegetation characterized by saguaro and yellow paloverde, and fire is potentially harmful to lowland desertscrub dominated by creosotebush and white bursage. Long-lived saguaro and paloverde are very sensitive to fire. They take decades to mature, and communities may require decades to centuries to reach their diverse species composition and physical structure after fire [47,112]. Creosotebush and bursage are more resilient, but repeated burning in communities dominated by these shrubs has converted large areas to annual grasslands in the desert Southwest [18,47,96].
Nonnative grass/fire cycle: Nonnative grasses often increase in dominance following fires [16,46,47,71,107]. As nonnative grasses increase in dominance following fire, repeated burning can convert native-dominated desert shrubland habitat into nonnative grassland. These grasslands are likely to burn repeatedly, establishing a nonnative grass/fire cycle. Reviews of the impacts of nonnative grasses on FIRE REGIMES and community composition, including descriptions of the nonnative grass/fire cycle, are available in these sources: [15,16,36,47,107].
As nonnative grasses establish and spread, fire-return intervals increase, and abundance of native shrubs decreases in desert shrublands, availability of white-throated woodrat habitat is likely to be negatively impacted, due to their dependence on native shrubs for food and cover.
Fire tolerance: Fire-related effects on some desert plants may be extreme, and fire recovery is generally long [100]. Shrubs that sprout from their base require several years to regrow after fire; shrubs that do not sprout may be completely killed [70]. Many shrubs and short-stature trees used by white-throated woodrats are vulnerable to fire [9,20,30,43,66,70,79,92,126,139]: White-throated woodrats commonly rely on creosotebush, mesquite, catclaw acacia, paloverde, and cacti for cover, food, and water (see Cover requirements and Food habits). Creosotebush [20,70], paloverde [30,79], saguaro [126], and prickly-pear [9,43,66,92,126,139,141] are typically killed by fire of any severity. It may take a century or more for saguaro and paloverde to develop from seed to large adult size [47,86]. Mesquite and catclaw acacia are more resistant to fire. Low-severity fires usually inflict no damage or partially kill the aboveground crown. High-severity fire may kill young plants, but mature plants are often top-killed and resprout [47,69,125,127,136]. For more information about fire effects on plants commonly used by white-throated woodrats, see the FEIS reviews for creosotebush, honey mesquite, velvet mesquite, catclaw acacia, yellow paloverde, blue paloverde, saguaro, and plains prickly-pear.
Availability of cover and food influence the abundance of small mammals after fire [74]. White-throated woodrats build flammable houses at the base of vegetation, and fire may destroy existing houses and the materials needed to build new houses. Fire may also decrease the food supply for white-throated woodrats. According to Simons [118], white-throated woodrats may have difficulty recolonizing areas after fire.
White-throated woodrat response to fire: In the following studies, white-throated woodrats were negatively affected by wildfire and prescribed fire due to fire-induced mortality of vegetation necessary for cover, food, and water. White-throated woodrats tend to prefer unburned sites over burned sites during the first few postfire years [12,85,89,118]. Although long-term studies are lacking, the long recovery time needed for many plant species upon which they depend suggests that impacts may be long-lasting.
White-throated woodrat density was higher on unburned sites compared to burned sites in a saguaro-paloverde plant community on the Tonto National Forest, Arizona. The dominant tree was paloverde, the dominant shrub species was bursage, and the dominant grasses and forbs were red brome, cutleaf filaree (Erodium cicutarium), desert Indianwheat (Plantago ovata), and whitemargin sandmat (Chamaesyce albomarginata). The wildfire occurred in June and burned 260 acres (105 ha), and the study began during fall of postfire year 1. The lower density of white-throated woodrats on burned sites probably resulted from lack of cover. The few white-throated woodrats caught on the burned areas were on rocky slopes where cutleaf filaree and desert Indianwheat occurred [85]:
Number of white-throated woodrats captured on unburned and burned sites in Arizona [85] Sample date Unburned Burned October, postfire month 4 21 6 January, postfire month 7 5 2 May, postfire month 11 19 10 September, postfire month 15 5 2 January, postfire month 19 2 2White-throated woodrats were rarely found on burned sites after wildfire in a desert sky island in the Mazatzal Mountains, Arizona. The spring wildfire killed more than 90% of the vegetation in a 237-km² area dominated by interior chaparral and desert scrub at low elevations (2,300-5,900 feet (700-1,800 m)) and Madrean evergreen woodland at higher elevations (>5,900 feet (1,800 m)). The study was conducted in postfire years 1, 2, and 3 [89]:
Number of white-throated woodrats captured in 3 postfire years on burned and unburned chaparral and Madrean evergreen woodland in the Mazatzal Mountains, Arizona [89] Burned chaparral Unburned chaparral Burned Madrean evergreen woodland Unburned Madrean evergreen woodland 1 10 0 6In 2 studies, white-throated woodrat populations decreased following prescribed fire [12,118]. In habitat dominated by paloverde, triangle bursage, and buckhorn cholla in the Tonto National Forest, Arizona, white-throated woodrat abundance and survival declined and remained low for 13 months after prescribed fire. The low-severity, early summer burn removed 50% to 73% of cover, and all 36 white-throated woodrat houses on the plot were destroyed. Prior to the burn, white-throated woodrat weekly survival was high (mean 0.96/week, n=4) on burned on unburned plots. At the time of the fire, survival of white-throated woodrats on the burned area was low (mean=0.20/week, n=not given). After the burn, survival remained low (mean=0.65/week, n=6) on the burned plot and high on the unburned plot (mean=0.97/week, n=6). Six months after the fire, no construction of new white-throated woodrat houses had occurred on burned sites, and 13 months after fire, only small, incomplete houses were built [118]:
Number of white-throated woodrats captured before and 13 months after a prescribed burn, Tonto National Forest, Arizona, P=<0.005 [118] Sample periodBurned
Unburned
Captures Individuals Captures Individuals Before fire 182 39 215 44 After fire 26 11 154 38The following table provides fire regime information on vegetation communities in which white-throated woodrats may occur, based on the habitat characteristics and species composition of communities white-throated woodrats are known to occupy. There is not conclusive evidence that white-throated woodrats occur in all of the habitat types listed, and some community types, especially those used rarely, may have been omitted. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Fire regime information for vegetation communities in which white-throated woodrat may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [77]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the PDF file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model. California Southwest Great Basin California Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics Percent of fires Mean intervalThe white-throated woodrat is a small rodent measuring an average of 12.9 inches (32.8 cm) and weighing an average of 188 g for females and 224 g for males [59,82]. With the exception of lactating females, white-throated woodrats are solitary and occupy separate houses [93,94,98,131,132]. They are primarily nocturnal [21,27,132] and are active year-round [131]. According to Brown and Zeng [23], maximum longevity for the white-throated woodrat is 45 months, and according to Newton [94], maximum longevity is 72 months.
Mating: The mating season of white-throated woodrats varies across their range. In Arizona, the mating season is from January to August [132]. In Big Bend National Park, Texas, mating occurs at least from January to November and may occur year-round [102]. In California, the mating season is in February and March, according to Rainey [104], and in March, April, and possibly May, according to Schwartz and Bleich [115]. The mating system of the white-throated woodrat is polygynous [93,94].
Gestation period and litter size: Gestation for white-throated woodrats lasts 37 to 38 days [108], and young are most often born in spring and early summer [22]. In Arizona, mean litter sizes were 1.95 young/litter (n=93 litters) [132] and 2.5 young/litter (n=27 litters) [115].
Development: Young white-throated woodrats are weaned 62 to 72 days after birth and reach sexual maturity 166 to 176 days after birth [108,115]. Weaning and sexual maturity of the subspecies Neotoma albigula venusta in western Arizona, Sonora, and Baja California occur earlier: young are weaned between 27 and 40 days, and reach sexual maturity 80 to 87 days after birth [115]. In Joshua Tree National Monument, California, young white-throated woodrats establish their own dens by August and September, several months after birth [22].
Home range and density: Descriptions of the home home range of the white-throated woodrat are lacking. The home range of 1 immature female white-throated woodrat on the Coconino National Forest, Arizona, was 47,760 ft² (4,437 m²) [56].
White-throated woodrat density may be governed by the number of suitable plants available for shelter, food, and water [21,22,128,132,142]. In Joshua Tree National Monument, there was a significant (P<0.001) positive relationship between white-throated woodrat density and teddybear cholla density, which provided shelter, food, and water [22]. In the Mesilla Valley of southern New Mexico, white-throated woodrat density was more dependent on plants that provided sufficient water and food than on plants that provided shelter [142].
White-throated woodrat density in various plant communities State Habitat Density (individuals/ha) Arizona Ponderosa pine 9.8 [55] Chaparral 12.8 [62] Desert scrub 5.7 [90] 11.95 [132] New Mexico Pinyon-juniper 5.8 [128] Texas Honey mesquite-tobosa (Pleuraphis mutica) 32.0 [92]Forest management: White-throated woodrats may benefit from coarse woody debris [55,56,116,117] and dense herbaceous understory vegetation in riparian areas [5]. In pinyon-juniper and ponderosa pine habitats, managing for retention of coarse woody debris may benefit white-throated woodrats by creating cover [1,55,56,116,117]. In 3 studies, logging treatments that retained slash yielded the highest number of white-throated woodrats [1,116,128]. White-throated woodrats depend on dense herbaceous understory vegetation in riparian areas of the lower Colorado River, Arizona [5]. Andersen and Nelson [5] suggest that resource managers consider the understory as well as overstory vegetation when rehabilitating degraded desert riverine systems.
Livestock grazing: In many cases, overgrazing by domestic livestock in the southwestern United States has converted native perennial grasslands to desert shrub communities dominated by creosotebush, mesquite, acacia, tarbush, and longleaf ephedra (Ephedra trifurca) [6,64,138]. Conversion of grasslands to shrublands appears to have negative [84,130], positive [25,33,53,65], or neutral effects [65] on the white-throated woodrat. Published opinions differ regarding the impact of white-throated woodrats on livestock production [54,90,132,137].
Negative effects: Livestock may negatively affect small mammals by trampling shelter sites, compacting soil, competing for food, and/or altering the vegetative community in a manner that influences habitat selection [65]. According to Bock and others [13], the strongest effects of livestock grazing on small mammals are probably those mediated by changes in cover. In a desert shrubland dominated by encroaching creosotebush and tarbush in southeastern Arizona, white-throated woodrat abundance increased slightly as desertified, formerly overgrazed habitat recovered to native perennial grasses. After livestock were removed, it took at least 20 years for native vegetation to begin to increase [130]. On the Jornada Experimental Range, removal of honey mesquite shrubs in addition to grazing resulted in decreased capture rates of white-throated woodrats compared to ungrazed plots where honey mesquite was retained [84].
Positive effects: White-throated woodrat numbers may increase as a result of grazing. In Chihuahuan desert grasslands, livestock grazing has resulted in a decrease in grass abundance and an increase in shrubs such as honey mesquite and creosotebush [25,53], which may provide more cover and food for white-throated woodrats. A decrease in grass cover can reduce fire size and frequency due to decreased fine fuel biomass and continuity, thus allowing further spread of prickly-pear and mesquite. An increase of prickly-pear and mesquite may result in more shelter sites for white-throated woodrats [33,132].
No effect: White-throated woodrats did not show a clear difference in abundance on grazed versus ungrazed plots in a desert marsh, San Simon Ciénega, on the border of Arizona and New Mexico. This response may have been a result of white-throated woodrats exploiting brush piles that were unaffected by grazing [65].
White-throated woodrat influences on livestock production: Effects of white-throated woodrats on livestock production have not been studied systematically. Opinions expressed in the literature vary, and no recent research on this subject was found for this review. According to two citations from the 1940s [90,132], white-throated woodrats rarely eat grass and other vegetation regarded as desirable to livestock and pose little threat to the livestock industry. In 1969, however, Wood [137] indicated that white-throated woodrats compete with livestock for forage in New Mexico, negatively affecting livestock carrying capacity. Glendening and Paulsen's [54] 1955 paper asserts that because white-throated woodrats store numerous velvet mesquite seeds, they may lower grass density and increase velvet mesquite density, negatively affecting livestock production.
Climate change: A significant (P<0.005) increase in air temperature over an 8-year study period corresponded with a significant (P<0.05) decrease in mean body mass of white-throated woodrats. The study was conducted in the transition zone between Chihauhuan Desert, Great Basin shrub steppe, and Great Plains grassland at the Sevilleta National Wildlife Refuge in New Mexico. According to the authors, further climatic change may have substantial impacts on the life history and ecology of white-throated woodrat at the Sevilleta National Wildlife Refuge. Smaller body size may force white-throated woodrats to depend on higher-quality food items which may increase energetic costs and competition when foraging [119].
Other: Herbicide may be used to control shrubs invading semidesert grasslands without impacting white-throated woodrat densities. Three years after application of tebuthiuron to control creosotebush in Arizona, white-throated woodrat densities were almost twice as high on tebuthiuron-treated plots compared to control plots [120].
In Organ Pipe Cactus National Monument, the presence of an occupied white-throated woodrat midden may favor persistence of nonnative buffelgrass (Pennisetum ciliare). Effective buffelgrass control required a minimum of 2 years on an experimental plot where one of more persistence factors existed. Persistence factors on the plot included a large number of old buffelgrass plants, location adjacent to a large source population, a previous burn, and occupation by a white-throated woodrat. Sites with no persistence factors might require only one buffelgrass eradication visit followed by monitoring and maintenance [113].
The white-throated woodrat occupies a variety of plant communities from sea level to 9,200 feet (2,800 m) [21,97,131,132] but is most common in Sonoran and Chihuahuan desert grassland and desert shrub habitats [21,37,90,94,131,132,137]. The white-throated woodrat is generally associated with creosotebush, mesquite, cacti (particularly prickly-pear and cholla (Cylindropuntia spp.)), catclaw acacia, and paloverde. These plants provide cover (see Cover) and succulent plant food (>50% water by weight) (see Food habits), the 2 most critical habitat requirements for white-throated woodrat [21,22,33,49,90,93,94,104,131,132].
White-throated woodrats prefer habitat with low tree canopy cover [1,14,45,116], high shrub [14,55] and rock cover [14,55,56,88,142], and coarse woody debris [1,49,97,106,116,128]. When available, natural and human constructed riparian habitat may be used by white-throated woodrats [4,5,35,45,91].
Tree, shrub, and rock cover: In several studies in Arizona, white-throated woodrats preferred low tree cover and high shrub, rock, and litter cover [1,14,45,116]. In ponderosa pine-Gambel oak habitat in the Hualapai Mountains in Arizona, white-throated woodrat presence was negatively associated with high tree cover and high herbaceous cover and positively associated with high shrub and rock cover. On plots where white-throated woodrats were trapped, mean tree canopy cover ranged from 30% to 57%, mean herbaceous cover ranged from 2% to 10%, mean shrub cover ranged from 5% to 19%, and mean rock cover ranged from 3% to 14% [14].
In desert riparian floodplain habitat at Montezuma Castle National Monument, Arizona, white-throated woodrats were more abundant in an active riparian channel and floodplain that had lower tree cover and a higher percentage of forbs and rocks than a mesquite bosque. The active riparian channel and floodplain was dominated by desert willow, velvet ash (Fraxinus velutina), Arizona sycamore (Platanus wrightii), and velvet mesquite. The mesquite bosque was dominated by velvet mesquite, catclaw acacia, and broom snakeweed [45].
Mean percent vegetation and ground cover in 2 white-throated woodrat habitats at Montezuma Castle National Monument, Arizona [45] Microhabitat variable Active riparian channel and floodplainIn pinyon-juniper woodlands in Grant County, New Mexico, total overstory density was more important than overstory species composition in influencing white-throated woodrat occurrence. The greatest densities of white-throated woodrat houses were on plots containing 376 to 750 overstory plants per hectare [128]:
Density of white-throated woodrat houses in relation to combined tree and shrub density and herbaceous plant production in Grant County, New Mexico [128] Overstory densityWhite-throated woodrats prefer rocky areas within forested habitat, including ledges, slides, cliffs, and canyons [14,55,56,88]. In a ponderosa pine forest on the Beaver Creek Watershed in the Coconino National Forest, all white-throated woodrats were captured within 210 feet (64 m) of rocky habitat [55,56]. In ponderosa pine-Gambel oak habitat in the Hualapai Mountains, white-throated woodrat presence was positively associated with high (3% to 19%) rock cover [14].
Riparian: The white-throated woodrat is well adapted to xeric habitats [132] but may use natural [5,45,91] and human constructed riparian areas when available [4,35].
Natural: At Montezuma Castle National Monument, white-throated woodrat abundance was generally greater in an active riparian channel and floodplain than a mesquite bosque that was 7 to 13 feet (2-4 m) above the channel and floodplain and not subject to flooding. The active riparian channel and floodplain was dominated by desert willow, velvet ash, Arizona sycamore, and velvet mesquite. The mesquite bosque was dominated by velvet mesquite, catclaw acacia, and broom snakeweed. Despite greater abundance of white-throated woodrat in the active riparian channel and floodplain, body weights of male white-throated woodrat were significantly (P<0.05) higher in the mesquite bosque, suggesting that it was "higher quality" habitat [45].
Although preferred habitat differed between male and female white-throated woodrats on the Santa Rita Experimental Range, Arizona, both genders showed some preference for riparian woodland typified by Arizona white oak and netleaf hackberry [91]:
Habitat and use of habitat by sex in the Santa Rita Experimental Range, Arizona [91] Plant association Cover of plant associations (%) Females trapped (%) Males trapped (%) Acacia-velvet mesquite grassland 46.2 2.2 10.9 Netleaf hackberry woodland 4.1 7.8 10.9 Arizona white oak-riparian woodlandHuman constructed: Construction of water developments in xeric habitat in Arizona may provide habitat and water for white-throated woodrats [4,35]. On the Cabeza Prieta National Wildlife Refuge in southwestern Arizona, white-throated woodrats were trapped most often in velvet mesquite thickets that grew closest to a human constructed water development. White-throated woodrats were trapped least often in habitat dominated by creosotebush and furthest away (distance not given) from the water development. No white-throated woodrats were trapped at a nearby dry water development [35].
White-throated woodrats also occupied a human constructed desert riparian habitat at No Name Lake on the Colorado River Indian Reservation on the Arizona side of the Colorado River. The area was cleared of nonnative tamarisk (Tamarix spp.) and 80% of the area was planted with native Fremont cottonwood and honey mesquite. Other vegetation included Goodding willow, blue paloverde (Parkinsonia florida), big saltbush (Atriplex lentiformis), and California palm (Washingtonia filifera) [4].
Coarse woody debris: Habitat with abundant coarse woody debris is preferred by white-throated woodrats for cover [45,97,106,116,128] (see Cover). In pinyon-juniper woodlands at the Piñon Canyon Maneuver site near Trinidad, Colorado, white-throated woodrats were captured most often in areas with coarse woody debris [106]. In an actively flooded riparian channel and floodplain at Montezuma Castle National Monument, white-throated woodrat occurrence was significantly (P<0.05) greater in areas containing coarse woody debris than areas without coarse woody debris [45].
In a pinyon-juniper woodland in the Gila National Forest, New Mexico, white-throated woodrats responded favorably to mechanical treatments that increased the amount of coarse woody debris. Of 4 treatments (untreated; bulldozed/piled/burned; bulldozed; and thinned), white-throated woodrats were most abundant on bulldozed plots and thinned plots, where slash accumulations were 2.5 to 3 times greater than on other plots. On bulldozed plots, Colorado pinyon, one-seed juniper, and alligator juniper trees were pushed over and left in place. On thinned plots, Colorado pinyon and juniper were cut to a minimum spacing of 20.0 feet (6.1 m) and left in place. The table below shows total numbers of woodrats on 4 plots [116]:
Total numbers of white-throated woodrats trapped on 4 pinyon-juniper sites, Gila National Forest, New Mexico [116] Untreated woodland Bulldozed/piled/burned Bulldozed Thinned 117a¹ 156ab 205b 183b ¹Values followed by different letters are significantly different (P< 0.05).
