375.

California Myotis

Myotis californicus

French: Murin de Californie / German: Kalifornien-Mausohr / Spanish: Ratonero de California

Other common names: Californian Myotis

Taxonomy. Vespertilio californicus Audubon & Bachman, 1842,

“ California,” USA.

Subgenus Pyzonix; lucifugus species group. Myotis californicus is close to M. ciliolabrum, M. melanorhunus, and M. leibii . Subspecies are poorly delimited and might not persist after assessment with modern techniques. Four subspecies recognized.

Subspecies and Distribution.

M.c.californicusAudubon&Bachman,1842—SWCanada(SEBritishColumbia),WUSA(EWashington,EOregon,Idaho,W&NCMontana,NEUtah,NE,C&SWCalifornia,EArizona,NewMexico,andWandarecordfromNTexas),andNMexicoincludingBajaCalifornia.

M.c.caurinusG.S.Miller,1897—SWCanada(SWBritishColumbia,includingHaidaGwaiiandVancouverI)andNWUSA(extremeSWAlaska,WWashington,WOregon,andNWCalifornia).

M.c.mexicanusSaussure,1860—CtoSWMexicoandCGuatemala.

M. c. stephensi Dalquest, 1946 — SW USA (Nevada, SE California, S & E Utah, SW Wyoming, W Colorado, and Arizona) and NW Mexico.

Descriptive notes. Head-body 38-48 mm, tail 32-45 mm, hindfoot 5-7 mm, ear 11-15 mm, forearm 31-35 mm; weight 3-3-5- 4 g. Fur of the California Myotisis dull rather than glossy. Dorsal pelage varies by region, ranging from pale yellow in southwestern deserts to dark chestnut-brown in Pacific Northwest (hairs always with darker bases); venter is paler. Face, ears, and membranes are blackish, being paler at bases of ears and around eyes. Ears are medium-sized; tragus is narrow and pointed. Tail extends no more than 1-2 mm past uropatagium, which is haired below knees but lacks fringe at posterior margin. Feet are very small; calcar is keeled. Skull has short rostrum, low coronoid processes, and small sagittal and lambdoidal crests. California Myotis can be differentiated from the Western Small-footed Myotis ( M. ciliolabrum) by its more rounded skull, narrower rostrum, and lower coronoid process. Chromosomal complement has 2n = 44 and FN = 50.

Habitat. Riparian woodlands, semiarid deserts and desert scrub, south-western arid grasslands, temperate forests (Pacific Northwest), and humid coastal forests and montane forests (California and Mexico).

Food and Feeding. California Myotis hunt by aerial hawking and are generally slow fliers that frequently change direction in pursuit of prey. Diet is composed primarily of Diptera and Lepidoptera, with smaller amounts of Coleoptera and Hemiptera, based fecal and stomach samples in Oregon. Feces contained primarily Trichoptera and some Coleoptera in British Columbia and primarily Diptera, Lepidoptera, Neuroptera, and Hymenoptera on Vancouver Island. They forage mostly in forest and canopy edges, above water, and well aboveground in open areas. Where sympatric with the Western Small-footed Myotis, California Myotis forage over or near water rather than rocky bluffs, avoiding competition. Foraging generally occurs higher than 3 m aboveground or water’s surface. They are less likely to forage when there are strong and gusty winds.

Breeding. California Myotis breed in late autumn in much of the northern part of the distribution where they hibernate, but they breed in early spring in California and southern parts of the distribution. In northern regions, females store sperm over winter until ovulation and fertilization in spring. Females gather into maternity colonies in narrowcrevices in spring and summer to give birth and raise a single young. Females were pregnant in late April and early May in south-western California. Maximum reproductive life span is 15 years.

Activity patterns. California Myotis roost primarily in narrow crevices on rocky hillsides, under bark, or in buildings and other man-made structures, but they can also be found in small desert shrubs and rock outcrops and on the ground. Depending on ambient temperatures at night, they have a bimodal or unimodal foraging pattern. At less than 15°C, they have a unimodal activity, with foraging times of 4-5 hours in the early night. At greater than 15°C, they have bimodal activity, foraging just after sunset and just before sunrise. They can foraging in temperatures as low as —8°C. In British Columbia, peak activity periods were 22:00-23:00 h and 01:00-02:00 h. Average minimum body temperature at which flight occurs is 26-3°C (range 22-4-29-6°C). Body weight is maximum weight in January and declines progressively until August. In autumn, storage of brown fat increases rapidly for winter. They remain active in winter but only for short periods before returning to hibernation. Calls are steep FM sweeps, with average start frequency of 68-3 kHz for males and 77 kHz for females, end frequency of 45-7 kHz for males and 51 kHz for females, peak frequency of 49-9 kHz for both sexes, and duration of 3 milliseconds for males and 2-1 milliseconds for females in Arizona.

Movements, Home range and Social organization. California Myotis roosts alone or in small groups, and females form small maternity colonies during reproductive season. They do not appear to be territorial and have been observed hunting in groups. They switch roosts often but apparently rarely return to a used roost.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The California Myotis is widespread and common throughout much of its distribution and does not appear to face any major threats.

Bibliography. Ammerman et al. (2016), Arroyo-Cabrales & Perez (2017), Baker & Patton (1967), Barclay & Brigham (2001), Bogan (1974), Brigham, Vonhof et al. (1997), Constantine (1998), Duke et al. (1979), Falxa (2007), Fenton & Bell (1979), Fenton, Merriam & Holroyd (1983), Fenton, van Zyll de Jong et al. (1980), Findley (1972), Gannon et al. (2001), Kellner & Harestad (2005), Krutzsch (1954), O'Farrell & Bradley (1970), O'Farrell & Schreiweis (1978), O'Farrell et al. (1967), Platt et al. (2018), Reeder (1949), Rodriguez & Ammerman (2004), Simpson (1993), Stadelmann et al. (2007), Straney et al. (1976), Studier et al. (1977), Whitaker et al. (1981), Woodsworth (1981), van Zyll de Jong (1984).