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Peromyscus boylii

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Brush Deermouse
(Peromyscus boylii)
Range
Taxonomic classification
Order:Rodentia
Suborder:Supramyomorpha
Infraorder:Myomorphi
Superfamily:Muroidea
Family:Cricetidae
Subfamily:Neotominae
Tribe:Peromyscini
Genus:Peromyscus
Binomial details
Peromyscus boylii (S. F. Baird, 1855)

Description

From Kalcounis-Rueppell & Spoon (2009): "Peromyscus boylii is of medium size with small ears and a long, slightly bicolored (dusky drab above, white to gray below—Zeveloff 1988) and slightly haired tail (such that the rings of hair on the skin are evident—Zeveloff 1988) that ends in a tuft of long hairs (Bradley and Schmidly 1999)."

From Schmidley & Bradley (2016): "A medium-sized, long-tailed deermouse; tail equal to or longer than head and body, sparsely haired, slightly tufted, and indistinctly bicolor, darker above; ankles dusky, the feet white; ears moderately long (19–22 mm from notch); proximal two-fifths of sole of hind foot hairy; upperparts pale cinnamon or hair brown to sepia; sides with narrow ochraceous buff lateral line; underparts white."

From Armstrong et al. (2010) for Colorado: "Brush mice are large, long-tailed, relatively short-eared, and bray-brown to buffy brown in color with a whitish gray venter. The sides are often brighter orange-brown. The feet are white but the ankles are gray or dusky. The indistinctly bicolored tail is longer than the length of the head and body. Hair on the tail is rather sparse, so scales are apparent." Additionally, "The hindfoot is usually longer than the ear."

Arrow points to the dusky ankle of Peromyscus boylii

External measurements

Length measurements are in millimeters (mm) and weight measurements are in grams (g), unless stated otherwise. If available, the sample size (n=) is provided. If a range is not provided and n= is not given, then the listed measurement represents an average.

Part of range Reference Total length Tail length Hindfoot length Ear length Mass
Arizona (Coconino Co.) Hoffmeister (1986) 189–222 (n=33) 95–115 (n=33) 21–24 (n=33) 18–22 (n=33)
California Jameson & Peeters (2004) 180–238 91–123 20–26 15–20 25–35
Colorado Armstrong et al. (2010) 180–220 80–115 20–24 15–22 20–30
Texas Schmidly & Bradley (2016) 197 103 22 22–36


Color variation

This section shows some of the color variation present in Peromyscus boylii. The location is provided for reference only. The individual shown does not necessarily represent the only color variant within the local population.

Skull

Peromyscus boylii has upper molars 1-2 with mesolophs, but the lower molars lack accessory lophs.

  • Dorsal view of the skull of Peromyscus boylii.
  • Lateral view of the skull of Peromyscus boylii. Lower mandible not shown.
  • Ventral view of the skull of Peromyscus boylii.
  • Upper incisors of Peromyscus boylii.
  • Dorsal view of the lower mandible of Peromyscus boylii.
  • Arrows point to the accessory lophs on the upper molars of Peromyscus boylii.
  • Lower molars of Peromyscus boylii lack accessory lophs.

Similar species

Comparison with Peromyscus attwateri

The Texas Deermouse (Peromyscus attwateri) is similar in appearance to Peromyscus boyli and was formerly treated as a subspecies of P. boylii. In Texas, Schmidly & Bradley (2016) note that "the most useful morphological features available in the field, and to those not trained in cytogenetics, are the larger hind foot (24–27 mm in attwateri and 20–23 mm in Texas-taken boylii) and the structure of the molar teeth. In attwateri, an accessory loph is present in both the upper and lower molars, but that structure is absent from the lower molars of boylii."

  • The lower molars of Peromyscus boylii lack accessory lophs, unlike in Peromyscus attwateri.
  • Arrows point to the accessory lophs in the first and second lower molars in the Texas Deermouse (Peromyscus attwateri).

Comparison with Peromyscus californicus

From Fargo & Laudenslayer (1995) for oak woodlands of the southern Sierra Nevada in Fresno County, California: "Most identifying characteristics of the two dominant Peromyscus species, brush mouse (P. boylii) and California mouse (P. californicus) overlapped considerably. Weight, body length, tail length, hind foot length, dorsal tail-stripe width, and ear length were usually sufficient for accurate species identification. Hind foot length and dorsal tail-stripe width were the most reliable of the identification criteria examined. For hind foot length, no significant difference was found between juveniles and adults within each species. Hind foot lengths overlapped slightly between species, ranging from 20 to 25 mm for brush mice and 24 to 28 mm for California mice. Dorsal tail-stripe width had the lowest overlap between species. All of the brush mice had dorsal tail-stripes less than or equal to half the tail circumference, and 98 percent of the California mice had dorsal tail-stripes greater than half. Use of hind foot length and dorsal tail-stripe width as key field identifiers was an expedient and accurate approach for distinguishing these two species."

Comparison with Peromyscus crinitus

The Canyon Deermouse (Peromyscus crinitus) differs from P. boylii in having a tail with a pronounced terminal tuft. While the length of tail> total length of body in P. boylii, the length of the tail relative to body length in P. crinitus varies by population.

Comparison with Peromyscus eremicus

From Hoffmeister (1986) for Arizona: "P. eremicus differs from P. boylii in less heavily haired and less bicolored tail, smaller ears, upper molars 1-2 without mesolophs."

Comparison with Peromyscus gambelli, P. leucopus, and P. sonoriensis

Peromyscus boylii can be differentiated from P. gambelli, P. leucopus, and P. sonoriensis by a length of tail > total length of body. In addition to having short tails, P. gambelli and P. sonoriensis also have strongly bicolored tails, whereas P. boylii does not.

Comparison with Peromyscus laceianus

From Bradley et al. (2015): "From P. boylii, P. laceianus differs in the following features: skull slightly smaller; rostrum relatively broader and heavier; braincase less vaulted; molar teeth slightly smaller; white instead of dusky ankles; posterior tip of nasals truncate rather than tapering in a V-shaped pattern; baculum with long cartilaginous spine at distal end instead of a short spine; 9–10 large biarmed chromosomes rather than 3–4."

Comparison with Peromyscus nasutus

From Schmidly & Bradley (2016): "it can be "distinguished from P. nasutus by smaller ears and shorter fur. The upper parts of P. nasutus are grayish brown or grayish buff.

Comparison with Peromyscus truei

From Kalcounis-Rueppell & Spoon (2009): East of the Sierra Nevada, P. boylii can be differentiated from P. truei by a length of tail > total length of body (Schmidly, 1977; Davis and Schmidly, 1994). Kalcounis-Rueppell & Spoon (2009) add that "west of the Sierra Nevada, where the tail of P. truei is longer than its head and body, P. boylii is distinguished from P. truei by ears that are 70–80% as long as the hind foot rather than longer than the hind foot, by a tail that is less heavily haired but with more pronounced annulations, and by auditory bullae that are less inflated (Hoffmeister 1981)." However, KE Mabry (personal communication, March 12, 2024) found that "in southeastern Napa County, California, Peromyscus truei have very short ears. Ear:HFL [ear to hindfoot length ratio] seems to be a reliable character elsewhere, but not there. [In southeastern Napa County], adult Peromyscus boylii generally have ears that are 17-19 mm and adult Peromyscus truei generally have ears that are >20 mm. I've compared ear length for genotyped animals, and the cut-off seems to be 19.5—above that, they are *almost* all Peromyscus truei and below they are *almost* all Peromyscus boylii. I also look at nose shape—Peromyscus boylii has a "pointy" nose and Peromyscus truei is more rounded. But there are definitely animals that are not clearly one or the other in hand."

  • Peromyscus boylii
  • Pinyon Deermouse (Peromyscus truei) from Madera County, California
  • Pinyon Deermouse (Peromyscus truei) from Apache County, Arizona. As several authors have noted, the length of the tail < total body length in individuals east of the Sierra Nevada. Note: ruler was added to the image and is an approximation.

References

Armstrong DM, Fitzgerald JP, Meaney CA. 2010. Mammals of Colorado, Second Edition. Denver (CO, USA): University Press of Colorado.

Baird SF. 1855-06-15. Characteristics of some new species of North American Mammalia, collected chiefly in connection with the U. S. surveys of a railroad route to the Pacific. Proceedings of the Academy of Natural Sciences of Philadelphia 7:333-336.

Bradley RD, Schmidly DJ. 1999. Peromyscus boylii. The Smithsonian Book of North American Mammals (D. E. Wilson and S. Ruff, eds.). Washington D.C. (USA): Smithsonian Institution Scholarly Press.

Bradley RD, Schmidly DJ, Amman BR, Platt RN, Neumann KM, Huynh HM, ... & Ordóñez-Garza N. 2015. Molecular and morphologic data reveal multiple species in Peromyscus pectoralis. Journal of Mammalogy 96(2): 446-459.

Davis WB, Schmidly DJ. 1994. The mammals of Texas. Austin (TX, USA). Texas Parks and Wildlife Press.

Fargo RJ, Laudenslayer WF. 1995. Morphological differences between two white-footed mice, Peromyscus boylii and Peromyscus californicus, in oak woodlands of Fresno county, California. 1995 Transactions of the Western Section of the Wildlife Society 31: 58-62. Link

Findley JS. 1975. Mammals of New Mexico. Albuquerque (NM, USA): University of New Mexico Press.

Hoffmeister DF. 1986. Mammals of Arizona. Tucson (AZ, USA): University of Arizona Press.

Jameson EW, Peeters HJ. 2004. Mammals of California (No. 66). Berkeley (CA, USA): University of California Press.

Kalcounis-Rueppell MC, Spoon TR. 2009. Peromyscus boylii (Rodentia: Cricetidae). Mammalian Species (838): 1-14.

Schmidly DJ. 1972. Geographic variation in the white-ankled mouse, Peromyscus pectoralis. The Southwestern Naturalist, 113-138.

Schmidly DJ. 1973. Geographic variation and taxonomy of Peromyscus boylii from Mexico and the southern United States. Journal of Mammalogy 54(1): 111-130.

Schmidly DJ. 1977. Mammals of Trans-Pecos Texas. College Station (TX, USA): Texas A&M University Press.

Schmidly DJ, Bradley RD. 2016. The mammals of Texas. Austin (TX, USA): University of Texas Press.

Thompson TG, Conley W. 1983. Discrimination of coexisting species of Peromyscus in south-central New Mexico. The Southwestern Naturalist, 199-209.

Zeveloff SI. 1988. Mammals of the intermountain west. Salt Lake City (UT, USA): University of Utah Press.