Chacetodipus formosus (Merriam, 1889)

Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Heteromyidae, Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona: Lynx Edicions, pp. 170-233 : 211

28.

Long-tailed Pocket Mouse

Chacetodipus formosus

French: Souris-a-abajoues longicaude / German: Langschwanz-Rauhaartaschenmaus / Spanish: Ratén de abazones de cola larga

Taxonomy. Perognathus formosus Merriam, 1889 ,

St. George, Washington Co., Utah, USA.

Based on detailed sequencing of nDNA and mtDNA genes, C. formosus is one of the three “ancient” clades of coarse-haired pocket mice. Seven subspecies recognized.

Subspecies and Distribution.

C.f.formosusMerriam,1889—WUSA(SWUtahandNWArizona).

C.f.cinerascensNelson&Goldman,1929—NWMexico(GulfcoastofNBajaCali-forniaStonearElMarmol).

C.f.incolatusHall,1941—WUSA(ENe-vadaandWUtah).

C.f.infolatusHuey,1954—NWMexico(GulfcoastofSBajaCaliforniatonearSantaRosalia).

C.f.melanurusHall,1941—WUSA(NECaliforniaandNWNevada).

C.f.mesembrinusElliot,1904—SWUSAandNWMexico(SCaliforniaandNEBajaCalifornia).

C. f. mohavensis Huey, 1938 — SW USA (Mojave Desert of S Nevada, SW Utah, NW Arizona, and S California).

Descriptive notes. Head-body 79-86 mm, tail 86-125 mm, ear mean 12 mm, hindfoot mean 25 mm; weight 17-25 g. There is no significant secondary sexual dimorphism. The Long-tailed Pocket Mouse is medium-sized for the genus, with crested, tufted, and bicolored tail that is longer than head-body length. Dorsal pelage is soft, lacking any stiff rump spines, and is slate gray with no lateral stripe; under parts are whitish. Distal tail crest is darker than dorsal pelage. Chromosomal complement has 2n = 36 and FN = 52. The Long-tailed Pocket Mouse may be found in the vicinity ofsix other species of the genus. It is smaller than the Peninsular Pocket Mouse (C. rudinors), which favors more open areas of pebbly soils that mark transitions from sandy flats to rocky alluvial slopes or “bajadas.” It only rarely overlaps with the California Pocket Mouse ( C. californicus ), which prefers chaparral vegetation and is more colorful, with a definite fulvous lateral stripe, and has conspicuous white rump spines. The Long-tailed Pocket Mouse more commonly occurs with the San Diego Pocket Mouse ( C. fallax ), which has conspicuous rump spines and a buffy lateral line. Where it occurs with the Spiny Pocket Mouse ( C. spinatus ) in a narrow zone of overlap), prominent and numerous spines that extend up to the shoulders easily identify the Spiny Pocket Mouse. The Desert Pocket Mouse ( C. penicillatus ) and the Little Desert Pocket Mouse ( C. arenarius ) are lighter in color than the Long-tailed Pocket Mouse and are restricted to sandy soils.

Habitat. Gravelly or rocky soils, frequently in or near canyons, slopes, or bases of cliffs in the Peninsular, Mojave, and Great Basin deserts. The ground is often covered in stones about the size of the Long-tailed Pocket Mouse. It is found in association with creosote bush ( Larrea , Zygophyllaceae ), blackbrush ( Coleogyne , Rosaceae ), burro-weed ( Ambrosia , Asteraceae ), mesquite ( Prosopis , Fabaceae ), shadscale ( Atriplex , Amaranthaceae ), sagebrush ( Artemisia , Asteraceae ), Mormon tea ( Ephedra , Ephedraceae ), and cholla ( Opuntia , Cactaceae ).

Food and Feeding. Diet of the Long-tailed Pocket Mouse consists largely of seeds of shrubs, annuals, and grasses, but it also includes smaller amounts of green vegetation and insects. Food items are collected in external, furlined cheek pouches and transported back to burrows, where they are stored in burrow caches. It does not need to drink water, subsisting entirely on water from its food and water produced as a byproduct of metabolism.

Breeding. Breeding season of the Long-tailed Pocket Mouse occurs in spring and continues into summer. Females normally produce one litter annually with 2-7 young. Reproductive activity is closely tied to spring vegetative growth, and a population can double in favorable years. In exceptional years, ¢.70% of females in a population are pregnant, litter sizes average c.6 young, offspring of the season breed later in the same year, and a fivefold increase in population size has been reported.

Activity patterns. The Long-tailed Pocket Mouse is nocturnal and terrestrial, and it is active throughout the year. Individuals may become torpid on cold nights and in winter.

Movements, Home range and Social organization. Male Long-tailed Pocket Mice are more mobile than females. There is intrasexual and intersexual overlap in home ranges, and home ranges are larger for males. The Long-tailed Pocket Mouse is solitary and likely polygynous and promiscuous. Males tended to increase their home ranges during the reproductive season. Home range sizes are estimated at 0-55 ha. Density has been estimated to be as high as 30 ind /ha.

Status and Conservation. Classified as Least Concern on The IUCN Red List.

Bibliography. Aquino & Neiswenter (2014), Best (1993a), Ceballos & Oliva (2005), Geluso (1999), Linzey, Timm, Alvarez-Castafeda, Castro-Arellano & Lacher (2008), Williams et al. (1993).

Figures

27. Hispid Pocket Mouse (Chaetodipus hispidus), 28. Long-tailed Pocket Mouse (Chacetodipus formosus), 29. Bailey's Pocket Mouse (Chaetodipus bailey), 30. Peninsular Pocket Mouse (Chaetodipus rudinoris), 31. Spiny Pocket Mouse (Chaetodipus spinatus), 32. California Pocket Mouse (Chaetodipus californicus), 33. San Diego Pocket Mouse (Chaetodipus fallax), 34. Little Desert Pocket Mouse (Chaetodipus arenarius), 35. Dalquest’s Pocket Mouse (Chaetodipus ammophilus), 36. Cerralvo Island Pocket Mouse (Chaetodipus siccus), 37. Desert Pocket Mouse (Chaetodipus penicillatus), 38. Chihuahuan Desert Pocket Mouse (Chaetodipus eremicus), 39. Sinaloan Pocket Mouse (Chaetodipus pernix), 40. Rock Pocket Mouse (Chaetodipus intermedius), 41. Nelson’s Pocket Mouse (Chaetodipus nelsoni), 42. Lined Pocket Mouse (Chaetodipus lineatus), 43. Goldman’s Pocket Mouse (Chaetodipus goldmani), 44. Narrow-skulled Pocket Mouse (Chaetodipus artus)

Subspecies and Distribution. C.f.formosusMerriam,1889—WUSA(SWUtahandNWArizona). C.f.cinerascensNelson&Goldman,1929—NWMexico(GulfcoastofNBajaCali-forniaStonearElMarmol). C.f.incolatusHall,1941—WUSA(ENe-vadaandWUtah). C.f.infolatusHuey,1954—NWMexico(GulfcoastofSBajaCaliforniatonearSantaRosalia). C.f.melanurusHall,1941—WUSA(NECaliforniaandNWNevada). C.f.mesembrinusElliot,1904—SWUSAandNWMexico(SCaliforniaandNEBajaCalifornia). C. f. mohavensis Huey, 1938 — SW USA (Mojave Desert of S Nevada, SW Utah, NW Arizona, and S California).