Perognathus flavus, Baird, 1855

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 : 204-205

20.

Silky Pocket Mouse

Perognathus flavus

French: Souris-a-abajoues soyeuse / German: Seidentaschenmaus / Spanish: Raton de abazones sedoso

Other common names: Baird's Pocket Mouse

Taxonomy. Perognatus [sic] flavus Baird, 1855 ,

El Paso, El Paso Co., Texas, USA.

Based on detailed sequencing of nDNA and mtDNA genes, P. flavus is a member of the flavus species group ofsilky pocket mice along with P. merriami , from which it is distinguished with great difficulty. It has been said that the two can be distinguished only by biochemical analysis. Until recently, the two were considered conspecific based on morphological and behavioral similarity. Electrophoretic analysis of allozymes among populations of both species in Texas and New Mexico revealed distinct complements in several zones of sympatry, with only a few probable hybrids from one locality in south-eastern New Mexico. In their 2010 analysis of mtDNA and nDNA sequences of samples from throughout the range of both species, S. A. Neiswenter and B. R. Riddle supported distinction ofthe two species, expanded the known area of distributional overlap, and revealed deeper phylogenetic structure in both the flavus species group and within P. flavus . Four major lineages were recovered that diverged in the late Miocene, 6-10 million years ago: two widespread and overlapping species ( P. flavus and P. merriami ), and two relictual, geographically restricted forms of equally ancient age in the central and southern Chihuahuan Desert. One of these (the “Meseta Central Matorral” lineage) is found in south-eastern Zacatecas and adjacent south-western San Luis Potosi; specimens from other localities in this vicinity have been assigned to the subspecies medius. The other (the “Southern Chihuahuan Desert” lineage) is more widespread across southern Coahuila, edging into eastern Chihuahua and eastern Durango, in the general vicinity of the Desierto de Mayran. Most of the specimens from other localities in the vicinity have been assigned to the subspecies pallescens, but northern and eastern populations are close to or within the range of P. merriami . It is likely that future studies will demonstrate that these two geographically restricted but relatively ancient lineages are distinct but morphologically cryptic species. Within P. flavus , in addition to the Meseta Central Matorral lineage, there are three basal clades that diverged an estimated 4-5 million years ago, in the Pliocene: the arid Valle de Tehuacan on the eastern margin of the Trans-Mexican Volcanic Belt in central Mexico; the central Great Plains; and the widespread Chihuahuan Desert—Colorado Plateau lineage. Thislatter lineage is divided into two lineages at the Rio Conchos in Chihuahua, with the southern Chihuahuan Desert lineage south of the Rio Conchos, and the lineage north of the Rio Conchos is further divided into the most recently diverged northern Chihuahuan Desert and Colorado Plateau lineages. Fourteen subspecies recognized.

Subspecies and Distribution.

P. f. flavus Baird, 1855 — SW USA and NC Mexico (SE Arizona, New Mexico, N & W Texas, and from NE Sonora and Chihuahua to NC Durango).

P. f. bimaculatus Merriam, 1889 — SW USA (WC Arizona).

P. f. bunkeri Cockrum, 1951 — SC USA (WC Great Plains of E Colorado, W Kansas, and W Oklahoma).

P. f. fuliginosus Merriam, 1890 — SW USA (vicinity of San Francisco Mts and Mogollon Plateau, NC Arizona).

P. f. fuscus S. Anderson, 1972 — NW Mexico (upper valley of the Rio Papigochic and watershed of the Laguna Bustillos, WC Chihuahua).

P. f. goodpaster: Hoffmeister, 1956 — SW USA (restricted distribution on the Mogollon Plateau of EC Arizona).

P. f. hopiensis Goldman, 1932 — SW USA (Four Corners region of SE Utah, SW Colorado, NE Arizona, and NW New Mexico).

P. f. medius Baker, 1954 — NC Mexico (SE Durango, SE Coahuila, Zacatecas, W San Luis Potosi, Aguascalientes, NE Jalisco, and Guanajuato).

P. f. mexicanus Merriam, 1894 — EC Mexico (Querétaro, Hidalgo, NE Michoacan, Puebla, Distrito Federal, Tlaxcala, WC Veracruz, and Morelos).

P. f. pallescens Baker, 1954 — NE Mexico (SE Chihuahua, W Coahuila, and NE Durango).

P. f. parviceps Baker, 1954 — WC Mexico (S Zacatecas and N Jalisco).

P. f. piperi Goldman, 1917 — NC USA (N Great Plains of E Wyoming and W Nebraska).

P. f. sanluisi Hill, 1952 — SW USA (San Luis Valley of SC Colorado).

P. f. sonoriensis Nelson & Goldman, 1934 — NW Mexico (disjunct distribution in coastal plains of WC Sonora).

Descriptive notes. Head—body mean 60 mm, tail mean 53 mm, ear mean 6 mm, hindfoot mean 17 mm; weight 5-10 g. There is no significant secondary sexual dimorphism. As in other silky pocket mice, pelage of the Silky Pocket Mouse is soft, fine, and full, with no hint of spines orstiff bristles; posterior one-half of sole of hindfoot has a sparse covering of short hairs; and tail is short and not tufted. Like most other silky pocket mice, the Silky Pocket Mouse has short, rounded ears without a lobed antitragus, and tail is without crest or tuft. The Silky Pocket Mouse is small-sized for the genus and is the smallest heteromyid species. Dorsal pelage is ocherous buff, yellowish-buff, or pinkish-buff finely lined with black hairs. Populations of the Silky Pocket Mouse that occur on dark-colored soils may be dark, as in a darkly pigmented population that occurs on a lava field in Arizona. The Silky Pocket Mouse has a clear buffy post-auricular patch, pale yellowish lateral line, and white under parts. Tail is shorter than head-body length and moderately bicolored. Chromosomal complement has 2n = 50 and FN = 86. In Chihuahua, where the Silky Pocket Mouse and Merriam’s Pocket Mouse (FP. merriama) are widely sympatric, the Silky Pocket Mouse has a slightly more lax pelage of pinkish (rather than orange) hue and tends to have mid-dorsal dark stripe. Post-auricular spots are larger and more conspicuous in the Silky Pocket Mouse, which also has a shorter tail and larger ears. Discriminant functions analysis of multiple cranial characters was able to correctly assign 88% of specimens from New Mexico and Texas to species.

Habitat. Semiarid to arid grasslands on a variety ofsoils (sandy to rocky) and in a variety of plant communities from the Great Plains, Colorado Plateau, and Chihuahuan Desert to the Valle de Tehuacan of the Hidalgan Desert (San Luis Potosi to Oaxaca). A disjunct subspecies (sonoriensis) occurs in the coastal plains of Sonora near Guaymas. The Silky Pocket Mouse reachesits highest densities in grasslands subjected to grazing and trampling, and it prefers open spaces between clumps of grass rather than a continuous grass cover. In keeping with this broad ecological tolerance, the Silky Pocket Mouse occurs around corn fields and other disturbed areas. Its common habitat characteristic is sparse or clumped grasses with open areas of bare ground. The Silky Pocket Mouse may use abandoned or even inhabited burrows of the Banner-tailed Kangaroo Rat ( Dipodomys spectabilis ) or other kangaroo rats, dig simple burrows in soil mounds of burrows of pocket gophers ( Geomyidae ), or occupy stick nests of woodrats (Neotoma). Burrows of Silky Pocket Mice are usually located beneath low shrubs and are relatively shallow (less than 30 cm) and simple, and openings may be open or closed during the day. Burrows often are dug where sand has accumulated at the bases of bushes.

Food and Feeding. Diet of the Silky Pocket Mouse consists largely of seeds of shrubs, annuals, and grasses, but it also includes smaller amounts of green vegetation and insects. It prefers smaller seeds. Food items are collected in external, furlined cheek pouches and transported back to burrows, where they are stored in burrow caches. Like all small silky pocket mice, it tends to husk seeds or separate seeds from seed heads before stuffing them in its cheek pouches. In some areas, the Silky Pocket Mouse frequents mounds constructed by harvester ants (Pogonomyrmex), apparently attracted by seeds collected by the ants. The Silky Pocket Mouse 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 Silky Pocket Mouse likely varies with latitude and even among populations in New Mexico and Arizona that have been studied. Breeding begins soon after emerging from winter torpor in burrows. Reproduction typically occurs in spring and summer. It appears that females usually have a single litter of 3—4 young/year (range 1-6), although females in the southern part ofits distribution probably have 2 litters/year. Gestation is 22-26 days. Females born late in summer do not breed until the following spring. Population turnoveris high, with most individuals living 1-2 years. In one population in New Mexico, ¢.50% of individuals lived for two months, 25% for six months, and a few for 20 months; average life span was 3-3 months. Captive individuals have lived for up to five years.

Activity patterns. The Silky Pocket Mouse is nocturnal and terrestrial, and it likely enters torpor for long periods in winter, particularly in northern parts of its distribution. In northern Arizona, it forages almost nightly throughout winter. Activity is reduced in winter, and individuals may not appear aboveground on particularly wet or cold nights. When inactive aboveground, they awake periodically from torpor to feed on seed caches. In warmer months in northern Arizona, greatest activity occurs at 18:00-22:00 h (i.e. warmest part of the night).

Movements, Home range and Social organization. Estimates of home range sizes of the Silky Pocket Mouse are 0-11-0-63 ha, with larger home ranges for males. Average range of movement is 62:5 m, and average dispersal distance during a lifetime is 202 m. Males and females segregate spatially, with males occupying higher ridges and females in flatter areas. As in most silky pocket mice that have been studied, adult Silky Pocket Mice are solitary, and there is no evidence of social grouping. Estimates of densities are 0-64-13 ind/ha.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The subspecies goodpasteri is considered threatened in Arizona due to its very isolated and restricted distribution.

Bibliography. Aquino & Neiswenter (2014), Best & Skupski (1994a), Chapman & Chapman (1999), Linzey, Timm, Alvarez-Castafieda, Castro-Arellano & Lacher (2008f), Neiswenter & Riddle (2010), Williams (1978a), Williams et al. (1993).

Figures

1. Salvin’s Spiny Pocket Mouse (Heteromys salvini), 2. Panamanian Spiny Pocket Mouse (Heteromys adspersus), 3. Mexican Spiny Pocket Mouse (Heteromys irroratus), 4. Jaliscan Spiny Pocket Mouse (Heteromys spectabilis), 5. Painted Spiny Pocket Mouse (Heteromys pictus), 6. Nelson's Spiny Pocket Mouse (Heteromys nelsoni), 7. Trinidad Spiny Pocket Mouse (Heteromys anomalus), 8. Overlook Spiny Pocket Mouse (Heteromys catopterius), 9. Paraguana Spiny Pocket Mouse (Heteromys oasicus), 10. Southern Spiny Pocket Mouse (Heteromys australis), 11. Ecuadorean Spiny Pocket Mouse (Heteromys teleus), 12. Gaumer’s Spiny Pocket Mouse (Heteromys gaumeri), 13. Desmarest’s Spiny Pocket Mouse (Heteromys desmarestianus), 14. Goldman’s Spiny Pocket Mouse (Heteromys goldmani), 15. Cloud-dwelling Spiny Pocket Mouse (Heteromys nubicolens), 16. Mountain Spiny Pocket Mouse (Heteromys oresterus)

Subspecies and Distribution. P. f. flavus Baird, 1855 — SW USA and NC Mexico (SE Arizona, New Mexico, N & W Texas, and from NE Sonora and Chihuahua to NC Durango). P. f. bimaculatus Merriam, 1889 — SW USA (WC Arizona). P. f. bunkeri Cockrum, 1951 — SC USA (WC Great Plains of E Colorado, W Kansas, and W Oklahoma). P. f. fuliginosus Merriam, 1890 — SW USA (vicinity of San Francisco Mts and Mogollon Plateau, NC Arizona). P. f. fuscus S. Anderson, 1972 — NW Mexico (upper valley of the Rio Papigochic and watershed of the Laguna Bustillos, WC Chihuahua). P. f. goodpaster: Hoffmeister, 1956 — SW USA (restricted distribution on the Mogollon Plateau of EC Arizona). P. f. hopiensis Goldman, 1932 — SW USA (Four Corners region of SE Utah, SW Colorado, NE Arizona, and NW New Mexico). P. f. medius Baker, 1954 — NC Mexico (SE Durango, SE Coahuila, Zacatecas, W San Luis Potosi, Aguascalientes, NE Jalisco, and Guanajuato). P. f. mexicanus Merriam, 1894 — EC Mexico (Querétaro, Hidalgo, NE Michoacan, Puebla, Distrito Federal, Tlaxcala, WC Veracruz, and Morelos). P. f. pallescens Baker, 1954 — NE Mexico (SE Chihuahua, W Coahuila, and NE Durango). P. f. parviceps Baker, 1954 — WC Mexico (S Zacatecas and N Jalisco). P. f. piperi Goldman, 1917 — NC USA (N Great Plains of E Wyoming and W Nebraska). P. f. sanluisi Hill, 1952 — SW USA (San Luis Valley of SC Colorado). P. f. sonoriensis Nelson & Goldman, 1934 — NW Mexico (disjunct distribution in coastal plains of WC Sonora).