401.

Silver-upped Myotis

Myotis albescens

French: Murin poudré / German: Silberspitzen-Mausohr / Spanish: Ratonero cenizo

Taxonomy. Vespertilio albescens E. Geoffroy Saint-Hilaire, 1806,

“ Paraguay.” Based on neotype selection,restricted by R. K. LaVal in 1973 to “Yaguaron, Paraguari, Paraguay.”

Subgenus Pizonyx; albescens species group. Monotypic.

Distribution. Widely distributed in Neotropics, from S Veracruz in Mexico, S through Central and South America to Peru, Bolivia, S Brazil, Paraguay, Uruguay, and N Argentina.

Descriptive notes. Head-body c¢. 46— 49 mm, tall 35-46 mm, ear 9-14 mm, hindfoot 6-9 mm, forearm 32-2-39- 5 mm; weight 4-8 g. South American populations show a trend toward increasing size southward. Fur is silky and long (dorsal fur 4-9 mm; ventral fur 3-8 mm). Dorsal hairs are bicolored, with dark brown bases and antique brown tips (one-fifth of total length), giving golden appearance; yellowish tips are less evident in a few specimens, in which dorsal fur can be nearly unicolored. Ventral hairs are strongly bicolored, with dark brown bases and generally white tips (one-third the length), giving frosted appearance; ventral fur often becomes progressively paler (whiter) from upper thorax to pelvic region. Ears are comparatively short, extending forward halfway from eye to nostril. Antitragal notch is barely evident. Tragus is long and slender, tapering slightly at tip. Membranes vary from cinnamon-brown to mummy brown; in some individuals, wing membrane has translucent brown appearance. Plagiopatagium is attached to feet by a broad band of membrane; fringe of hairs along trailing edge of uropatagium is present; and upper and lower surfaces of uropatagium are barely covered with hairs. Skull is moderate in size (greatest length of skull 13-1-15- 2 mm); parietal is normally inclined forward; occipital region is generally rounded posteriorly; braincase is globose; sagittal crest is generally absent, but when present,it is very low; lambdoidal crests are generally present, with low to medium development; forehead slopeslittle; rostrum is narrow relative to braincase; postorbital constriction is great relative to width of braincase. P° is generally aligned with P* and is visible in profile; hypocone on M' and M? is absent or poorly developed. Bacula is large, and individual variation is mostly in depth, not shape. Bacular measurements are length 0-85-0-90, depth 0-30-0-41, and width 0-37-0-50. Chromosomal complement has 2n = 44 and FN = 50, with four metacentric pairs and 17 acrocentric pairs of autosomes. X- and Y-chromosomes are submetacentric.

Habitat. Tropical rainforests, savannas, Chacoan scrublands, thorn scrub lowlands, evergreen forests, open habitats (e.g. wetlands and grasslands), and also secondary forests, agricultural landscapes, and semi-urban areas from sea level up to elevations of ¢. 1500 m (most commonly below 500 m). The Silver-tipped Myotis is apparently more abundant in areas that are flooded at least part of the year.

Food and Feeding. The Silver-tipped Myotis forages in forested areas and over water. Diets include various insects, especially Coleoptera, Diptera, Hemiptera, Homoptera, Hymenoptera, Lepidoptera, Neuroptera, Trichoptera, and other arthropods, such as spiders ( Araneae). Fish scales also have been reported in stomach contents. It has a trawler foraging style,flying a few centimeters above water orflat surfaces, using highintensity echolocation calls to detect, track, and assess targets, and capturing prey with its feet. In the Brazilian Amazonia, it predominantly forages in forest canopies and subcanopies, but in riparian forest or near water bodies, it mostly uses space closest to the ground or water surface.

Breeding. The Silver-tipped Myotis is polyestrous, and mating occurs 2-3 times annually. In Paraguay, spermatozoa were present in reproductive tracts of females at the beginning of the reproductive season in May; ovulation,fertilization, and implantation occurs c¢.1-3 months after copulation, indicating possible sperm storage and delayed fertilization; first parturition peak occurs in October, followed by copulation and second pregnancy, and possible third pregnancy in January-March. First gestation lasts c.3 months, and second and third gestations might be shorter. Following third peak, reproductive activity declines until beginning of a new annual cycle. Lactation lasts c.1 month, and lactating females were collected in Paraguay in October-December but also May-June during second and third breeding periods. Pregnant females have been reported in January in Mexico, January and July in Central America, June-September in northern South America, and December—February in south-eastern Brazil and northern South America. In Peru, parturition occurred during dry and wet seasons in eastern lowlands and only during dry season on the Pacific slope. Females have one young per pregnancy. Lactating females also were reported in February-April and November in northern South America; October in south-eastern Brazil; and September— November in southern South America. Individuals reach sexual maturity at c.1 year of age, but females can mate at c¢.2 months.

Activity patterns. Silver-tipped Myotis are nocturnal, emerging soon after sunset. Activity peaks occur immediately after dusk and just before dawn, periods that correspond with greatest abundance offlying diurnal and nocturnal insects. Natural roosts include hollow trees, under bark of trees, trunks, cracks, and crevices in rocks, and rocky cliffs. It is frequently found in human buildings, including attics, under roofs, under palm logs and roofs of palm-thatched huts, and in locations with some natural light and exposure, such as outer walls of buildings or open-sided attics. Captures and roosts are associated with areas near or around water. Wing morphology and echolocation frequency are typical of aerial insectivore that uses using cluttered spaces. Echolocation calls show FM initial component terminating with short CF component. Mean call parameters in South America are start frequency of 92.7 kHz (84-8-100-8 kHz), end frequency of 51-4 kHz (47-4-56-5 kHz), peak frequency of 64 kHz (57-3-72-6 kHz), bandwidth of 41-3 kHz (34-1-48 kHz), and call duration of 2-4 milliseconds (1-9-3 milliseconds).

Movements, Home range and Social organization. The Silver-tipped Myotis forms small or large groups in roosts; solitary individuals are uncommon. Colonies are mixed-sex. It can cohabit the same roost with Argentine Serotines ( Eptesicus furinalis), Common Black Myotis ( M. nigricans), Riparian Myotis (M. riparius), Sinaloan Mastiff Bats (Molossus sinaloae), Dwarf Dog-faced Bats (Molossops temminckii), and Black Bonneted Bats (Eumops auripendulus), among others.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Silvertipped Myotis is widespread and presumably has a large population.

Bibliography. Arias-Aguilar et al. (2018), Ascorra et al. (1996), Barquez, Diaz, Samudio & Arroyo-Cabrales (2016), Braun et al. (2009), Fenton & Bogdanowicz (2002), Gamboa & Diaz (2019), Kalko et al. (1996), LaVal (1973b), Lopez-Gonzélez et al. (2001), Marques et al. (2016), Moratelli & Morielle-Versute (2007), Moratelli & Oliveira (2011), Moratelli, Dewynter et al. (2015), Moratelli, Gardner et al. (2013), Myers (1977), Simmons (2005), Whitaker & Findley (1980), Wilson (2008b).