394.

Gray Myotis

Myotis grisescens

French: Murin gris / German: Graues Mausohr / Spanish: Ratonero gris

Other common names: Gray Bat

Taxonomy. Myotis grisescens A. H. Howell, 1909,

“Nickajack Cave, near Shellmound, Marion County, Tennessee,” USA.

Subgenus Pizonyx; albescens species group (24 species). Monotypic.

Distribution. SE USA, in Missouri, Kansas, Oklahoma, Illinois, and Indiana S to Alabama and NW Florida, and E to W Virginia and W North Carolina.

Descriptive notes. Head-body c.47 55 mm, tail 33-41 mm, ear 13-16 mm, hindfoot 8-10 mm, forearm 40-6-45- 8 mm; weight 7-16 g. Dorsal fur ranges from slate-gray to russet brown; ventral fur is lighter than dorsum, with gray or buffy bases and slighter paler tips. Traditionally, two color morphs have been described: gray (most frequent in July-August) and russet (most frequent in females in May andJuly). Russet morph probably occurs when ammonia fumes in summer roosts fade slate-gray winter coat. Ears are comparatively short, extending forward halfway from eye to nostril, and tragus has bluntly pointed tip. Membranes are dark brown, and plagiopatagium is attached to foot at ankle. There is no keel on calcar. Skull is moderate in size (greatest length of skull 15-5-16- 4 mm), long, and broad; palate is broad; upslope profile of forehead is less pronounced than in other North American Myotis; occipital region is rounded dorsally; and sagittal and lambdoidal crests are present and well developed. Chromosomal complement has 2n = 44 and FN = 50, with four submetacentric and 17 acrocentric autosomes. X- and Y-chromosomes are submetacentric.

Habitat. Karst areas with limestone caves and deciduous forests.

Food and Feeding. Gray Myotis foraged among trees in riparian vegetation and over waterways, catching insects in flight c¢. 5 m off the water or at ground surface. Diet consists of several genera and at least six species of mayflies (Ephemeroptera) and other aquatic insects, such as caddisflies (Trichoptera) and midges ( Diptera). Other prey includes lepidopterans, coleopterans, orthopterans, hemipterans, homopterans, mecopterans, neuropterans, odonatans, plecopterans, thysanopterans, hymenopterans, and spiders.

Breeding. Gray Myotis are polygynous, and mating occurs in autumn shortly after they enter hibernation caves. Females store sperm all winter, and fertilization is delayed until they emerge in spring. Implantation of one embryo almost always occurs in the right uterine horn, which is larger than the left horn. Pregnancy lasts ¢.50-60 days in April-May. During this period, females roost in maternity caves, and adult males and subadults of both sexes roost in bachelor caves. Females give birth in June. Gray Myotis are born completely naked, with their eyes closed, and weigh 2-4- 3-4 g. Growth rates of young vary with temperature in maternity roosts; neonates in warmer roosts grow more rapidly. Weaning occurs at ¢.2 months old, but only a few females are still lactating at the end of July. Young begin to fly ¢.20-25 days after birth in August. Sexual maturity is late, and male and female reproductive cycles are asynchronous. Females do not mate until two years old. Spermatogenesis in males begins in May of their second year oflife and is completed by September, preceding ovulation by c¢.7 months.

Activity patterns. Gray Myotis are emerge from diurnal roosts at dusk, concentrating activity in the first four hours after sunset. A second peak of activity can occur just before dawn. Annual activity can be separated into spring migration (late March to late May); summer period (late May to late August), including a subunit, the maternity period (early June to early July); fall migration (late August to late November); and hibernation or winter period (late November to late March). Except for occasional reports of some individuals in an abandoned mines and buildings, Gray Myotis do not generally roost in trees or man-made structures, which leads to extremely restricted roosting opportunities. Due to its requirements for specific cave types, it can use less than 5% of available caves—95% ofthe total population hibernates in only nine caves in Tennessee, Missouri, Kentucky, Alabama, and Arkansas. It is one of the few bats that roosts in caves in winter and summer and is highly selective for caves providing specific temperatures and roost conditions. It prefers humid and warm (14-25°C) summer caves, usually with large streams running through them. These caves are within 1-2 km of a majorriver or lake. Winter caves often have multiple entrances, good airflow, and temperatures of 6-11°C.

Movements, Home range and Social organization. Gray Myotis move seasonally between summer and winter caves, and they make long movements between diurnal roosts and foraging areas. Individuals from a hibernaculum in Kentucky moved seasonally to ten caves in Kentucky, Illinois, and Tennessee, covering 16,905 km * and moving at least 164 km. Individuals from hibernaculum in northern Tennessee migrated 775 km to a summer roost in Florida. Reports for other regions indicate that average one-way migration is 200 km. Transit or stopover caves are used along the way. Foraging individuals have been found as far as 25 km from their summer roosts. In general, females are relatively sedentary at maternity caves; males moved among caves as far as 30 km in the vicinity of maternity caves. Gray Myotis are colonial and form aggregations of up to 250,000 individuals in winter caves. They hibernate during winter, and densities can reach more than 1500 ind/m?. Bachelor caves are 1-35 km away from maternity caves. Populations are divided into discrete colonies with strong roost philopatry.

Status and Conservation. Classified as Vulnerable on The IUCN Red List. Despite its large population size, the Gray Myotis is vulnerable to potential massive mortality from White-nose Syndrome, caused by an exotic pathogenic fungus (Pseudogymnoascus destructans). Spread of this pathogen in eastern North America is threatening several species besides the Gray Myotis . Up to the 1990s, population decline was greater than 50%, and current scenarios are not favorable for many populations. Considering a time period of three generations (30 years), including the past twelve years and 18 years in the future,it is likely to decline by more than 30% across its distribution. There are several recovery programs, but long-term results are unknown.

Bibliography. Baker & Patton (1967), Barbour & Davis (1969), Best, Milam et al. (1997), Decher & Choate (1995), Elder & Gunier (1978), Guthrie (1933a, 1933b), Hall, E.R. (1981), Hall, J.S. & Wilson (1966), Hoffmeister (1989), Howell (1909), Lacki et al. (1995), LaVal & LaVal (1980c), LaVal et al. (1977), Solari (2018l), Timmerman & McDaniel (1992), Tuttle (1975, 1976), Wilson & Ruff (1999).