Perognathus fasciatus Wied-Neuwied 1839

22. Olive-backed Pocket Mouse Perognathus fasciatus French: Souris-a-abajoues des plaines / German: Oliv-Seidentaschenmaus / Spanish: Ratén de abazones de dorso oliva Taxonomy. Perognathus fasciatus Wied-Neuwied, 1839, Buford, Williams Co., North Dakota, USA. Based on detailed sequencing of nDNA and mtDNA genes, P.fasciatus is a member of the fasciatus species group ofsilky pocket mice along with P. flavescens, from which it is distinguished by its olivaceous dorsal color. Chromosomal complement has 2n = 44 and FN = 48. This karyotype differs from that of P. flavescens in that the Xand Y-chromosomes are both uniarmed (acrocentric). Three well-differentiated clades of P. fasciatus are indicated by genetic analysis: a clade that is widespread across the northern Great Plains and the Wyoming Basin; one thatis restricted to the Wyoming Basin (corresponding to callistus); and a third along the Front Range of the Rocky Mountains in Colorado that correspondsto the previously recognized subspecies infraluteus, which was synonymized underfasciatus based on morphological similarity. Two subspecies recognized. Subspecies and Distribution. P.f.fasciatusWied-Neuwied,1839—SCCanadaandCUSA(GreatPlainsfromSEAlberta,SSaskatchewan,SWManitoba,MontanaandNorthDakotatoMinnesotaborder,andStoWyomingandSCColorado). P. f. callistus Osgood, 1900 — WC and SW USA (Uintah, Bridger, and Great Divide basins of SW Wyoming, NE Utah, and NW Colorado). Descriptive notes. Head—body mean 72 mm, tail mean 65 mm, ear mean 7 mm, hindfoot mean 17 mm; weight 8-14 g. There is no significant secondary sexual dimorphism. As in othersilky pocket mice, pelage of Olive-backed 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. The Olive-backed Pocket Mouse has short, rounded ears without a lobed antitragus, and tail is without crest or tuft. It is medium-sized for the genus. Dorsal pelage ranges from dark, almost blackish, olivaceous in the north-east to pale buff in the south, with a buffy post-auricular spot, bright yellowish lateral line, and white (occasionally buff) under parts. Tail is shorter than head-body length and moderately bicolored. The Olive-backed Pocket Mouse is significantly larger than the Silky Pocket Mouse (P. flavus). Habitat. Grassland, shrub-steppe, and desert scrub habitats of the northern Great Plains and adjacent intermountain basins to the west, up to elevations of¢.2500 m. The Olive-backed Pocket Mouse prefers sparsely vegetated, open habitats with loose sandy to clayey soils. Its distribution extends south in grasslands along the western margin of the plains abutting the Rocky Mountains, where it is narrowly sympatric with the Plains Pocket Mouse (P. flavescens) and the Silky Pocket Mouse, and extends east to the transition from mixed-grass to tall-grass prairies, where it is sympatric along a narrow band with the Silky Pocket Mouse. Excavated burrows of Olive-backed Pocket Mice had extensive tunnel systems with multiple nest and seed-cache chambers, extending to a depth of 2 m and covering an area with a diameter of about 6 m; burrow entrance was located on slightly elevated ground. Food and Feeding. The Olive-backed Pocket Mouse feeds largely of seeds of shrubs, annuals, and grasses, but it also includes smaller amounts of green vegetation and insects in its diet. 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, the Olive-backed Pocket Mouse tends to husk seeds or separate seeds from seed heads before stuffing them into cheek pouches. 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 Olive-backed Pocket Mouse occurs in May—August, with a lull in June, suggesting that there may be more than one litter per season. Females have been captured with embryos and placental scars. Gestation is c.4 weeks. Average litter sizes are 4-6 young (range 2-9). Activity patterns. The Olive-backed Pocket Mouse is nocturnal and terrestrial, and it enters torpor during winter. In Canada, it appears to remain underground in its burrow from mid-October to mid-April. When inactive, Olive-backed Pocket Mice likely arouse from time to time to eat stored seeds from caches. Movements, Home range and Social organization. Estimates of densities of Olivebacked Pocket Mice are 0-6-4 ind/ha. Status and Conservation. Classified as Least Concern on The IUCN Red List. Bibliography. Aquino & Neiswenter (2014), Linzey & NatureServe (Hammerson) (2008j), Manning & Jones (1988), Neiswenter & Riddle (2011), Riddle (1999), Williams (1978a), Williams & Genoways (1979), Williams et al. (1993).

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