Perognathus inornatus, 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 : 203-204

18.

San Joaquin Pocket Mouse

Perognathus inornatus

French: Souris-a-abajoues du San Joaquin / German: San-Joaquin-Seidentaschenmaus / Spanish: Raton de abazones de San Joaquin

Other common names: Salinas Pocket Mouse

Taxonomy. Perognathus inornatus Merriam, 1889 ,

Fresno, Fresno Co., California, USA.

Based on detailed sequencing of nDNA and mtDNA genes, P. inornatus is a member of the longimembris species group of silky pocket mice along with P. longimembris and P. amplus . Based on published and unpublished information, at least two and possibly three species are currently included within the San Joaquin Pocket Mouse, and there has been a history of confusion about relationships and distributions of P. inornatus and P. longimembris . For example, the subspecies psammophilus was previously allocated to P. longimembris , and that species’ subspecies longimembris was depicted as occurring along the western side of the San Joaquin Valley. Type locality of P. longimembris (at which no silky pocket mice have been collected in well over a century) is in a position where either species might occur or have occurred. Preliminary karyotypic, molecular, and morphometric analyses indicate that all populations ofsilky pocket mice from north of the Transverse Ranges are P. inornatus , as are populations in the extreme north-western corner of the Mojave Desert. The two species appear to be sympatric over ¢.50 km near the junction of Kern, Los Angeles, and San Bernardino counties. These pocket mice are larger, with shorter tails, than P. longimembris . The Mojave Desert populations of P. inornatus (2n = 52) are most closely related to those along the coastal valleys and western edges of the San Joaquin Valley, up to San Francisco Bay (2n = 56). These populations are generally larger, with longertails, than other populations of P. inornatus . The southern San Joaquin (2n = 50), central San Joaquin (2n = 50), and northern San Joaquin Valley populations (2n unknown) appear to represent three closely related forms, of uncertain relationship with the southern Sacramento Valley population (2n = 60) farther north. Three subspecies recognized.

Subspecies and Distribution.

P.i.inornatusMerriam,1889—WUSA(SacramentoandSanJoaquinvalleys,SWCalifornia).

P.i.neglectusTaylor,1912—SWUSA(WedgeofSanJoaquinValleyfromSuisunBayStotheNWcorneroftheMojaveDesert,SWCalifornia).

P. i. psammophilus von Bloeker, 1937 — SW USA (Salinas Valley in the S Coast Range, SW California).

Descriptive notes. Head—body mean 73 mm, tail mean 75 mm, ear mean 8 mm, hindfoot mean 20; weight 7-12 g. There is no significant secondary sexual dimorphism. As in other silky pocket mice, pelage of the San Joaquin Pocket is soft, fine, and full, with no hint of spines orstiff bristles; posterior one-half ofsole of hindfoot has sparse covering of short hairs; and tail is short. The San Joaquin Pocket Mouse has short, rounded ears without lobed antitragus, and tail is without crest or tuft. The San Joaquin Pocket Mouse is medium-sized for the genus. Dorsal pelage is ocherous buff to pinkish buff, overlaid with blackish hairs; extent of overlay varies among subspecies. The San Joaquin Pocket Mouse has an indistinct buffy post-auricular patch, pale yellowish lateral line, and white under parts. Tail is slightly longer than head-body length and nearly unicolored. Chromosomal complement varies among and within subspecies, with 2n = 50-60 and FN = 86-88.

Habitat. Arid annual grassland, savanna, and desert-scrub situations in the Sacramento and San Joaquin valleys and small valleys along the Coast Ranges of California. The San Joaquin Pocket Mouse occurs in natural and weedy situations, at sites with sagebrush ( Artemisia , Asteraceae ), sage ( Salvia , Lamiaceae ), filaree ( Erodium , Geraniaceae ), oats ( Avena , Poaceae ), and brome ( Bromus , Poaceae ), usually in areas with fine-textured soils. At the northern extreme of its distribution, it inhabits chamise ( Adenostoma , Rosaceae ) and buckbrush ( Ceanothus , Rhamnaceae ) on rocky slopes. Most sites are instead flat, sandy, and with scattered low vegetation dominated by annuals. Burrows of the San Joaquin Pocket Mouse are conspicuous in low grass, with small openings (2-3 cm), usually in sandy soils near bases of bushes, with a nest chamber. Burrows are plugged during the daytime. San Joaquin Pocket Mice also inhabit burrows of Heermann’s Kangaroo Rat ( D. heermanni ).

Food and Feeding. Diet of the San Joaquin 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, such as the minute seeds of grasses, sagebrush, and saltbush ( Atriplex , Amaranthaceae ). Food items are collected in external, fur-lined 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. The San Joaquin Pocket Mouse does not need to drink water, subsisting entirely on water from its food and water produced as a byproduct of metabolism.

Breeding. The San Joaquin Pocket Mouse breeds in March—July, producing at least 2 litters/year, each with 4-6 young.

Activity patterns. The San Joaquin Pocket Mouse is nocturnal and terrestrial, spending the day belowground in its burrow and foraging on the surface at night. It is not a skilled climber. It appears to enter torpor for varying periods in response to cold surface temperatures or low food supply, and it is not usually found on the surface in October, January, and March.

Movements, Home range and Social organization. Estimates of home range sizes of the San Joaquin Pocket Mouse are 0-01-0-04 ha, with larger home ranges on sites not grazed by cattle. As in most silky pocket mice that have been studied, adult San Joaquin Pocket Mice are solitary, and there is no evidence ofsocial grouping. Estimates of densities are 0-4-7-3 ind/ha.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Nevertheless, much of the natural habitat of the San Joaquin Pocket Mouse has been degraded, fragmented, or destroyed by extensive agricultural development. According to unpublished data from 2004, the three subspecies were known from c.50 locations that represented no more than three-dozen distinct occurrences and not all of those were extant populations. At this point,it is not even clear how many cryptic species are actually present, or their distribution and conservation status.

Bibliography. Aquino & Neiswenter (2014), Best (1993a, 1993b, 1999a), Linzey & NatureServe (Hammerson) (2008k), 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.i.inornatusMerriam,1889—WUSA(SacramentoandSanJoaquinvalleys,SWCalifornia). P.i.neglectusTaylor,1912—SWUSA(WedgeofSanJoaquinValleyfromSuisunBayStotheNWcorneroftheMojaveDesert,SWCalifornia). P. i. psammophilus von Bloeker, 1937 — SW USA (Salinas Valley in the S Coast Range, SW California).