389.

Riparian Myotis

Myotis riparius

French: Murin des ruisseaux / German: Ufermausohr / Spanish: Ratonero ripario

Taxonomy. Myotis simus riparius Handley, 1960,

“Facarcuna Village, 3,200 fi. [= 975 m], Rio Pucro, Darién, Panama.”

Subgenus Pyzonix; ruber species group. Phylogenetic reconstructions using mitochondrial and nuclear genes indicated the distinction of M. riparius from M. simus and other congeners. Marked geographical variation occurs in cranial and external morphology. Monotypic.

Distribution. Widely distributed in Neotropics, occurring from S Honduras, Nicaragua, Costa Rica, and Panama S into all South American countries, except Chile; also on Trinidad I.

Descriptive notes. Head-body ¢. 43-45 mm, tail 28-48 mm, ear 10-14 mm, hindfoot 6—10 mm, forearm 32-3-39- 8 mm; weight 4-7 g. The Riparian Myotis is morphologically similar to its Neotropical congeners. Fur is long (dorsal fur 5-9 mm; ventral fur 4-8 mm) and woolly. Dorsal hairs are unicolored, without contrast between bases and tips. Ventral hairs are bicolored, with dark brown bases, yellowish tips, and strong contrast between bases and tips. Specimens from Central America and Amazon Basin generally have reddish brown or cinnamon-brown dorsal fur, with a few individuals having brownish or blackish dorsal fur. Most individuals from south-eastern Brazil, Paraguay, and Argentina have brownish or blackish dorsal fur, with a few reddish brown or cinnamon-brown individuals. Ears are comparatively short, extending forward halfway from eye to nostril. Antitragal notch is barely evident. Tragus is pointed,slightly curving outward above and convex below, with small triangular lobule at outer base (length 4-11 mm). Membranes are mummy brown; plagiopatagium is broadly attached to foot at bases oftoes. Fringe of hairs along trailing edge of uropatagium is absent; upper and lower surfaces of uropatagium are barely covered with hairs. Baculum is narrow and shallow, with pointed shaft, but widens suddenly near proximal end. Skull is mediumsized (greatest skull lengths 13-2-15- 2 mm); parietalis inclined forward; occipital region is generally flattened posteriorly; sagittal crest is generally present, ranging from low to high; lambdoidal crests are always present, ranging from low to medium; P? is generally aligned with P* and P*, and visible in profile view but might be displaced lingually, being visible or not. Height ofskull crests and P* position vary geographically. Most individuals from Central America, Amazon Basin, and Guiana Shield have medium to high sagittal and lambdoidal crests, and occipital region is flattened posteriorly. Populations from south-eastern Brazil, Paraguay, and Argentina tend to have low to medium sagittal and lambdoidal crests, and occipital region is slightly rounded. P? is either crowded lingually or positioned in tooth row but not visible labially, more frequently in individuals from northern localities. In individuals from south-eastern Brazil, P? is generally in tooth row and visible labially. Chromosomal complement has 2n = 44 and FN = 50, with three large and one small metacentric and 17 acrocentric pairs of autosomes. X-chromosomeis medium submetacentric, and Y-chromosome is small acrocentric.

Habitat. Wide variety of habitats such tropical rainforests, savannas, xerophytic formations, primary forests, and areas with different levels of human disturbance, including agriculturalfields, from sea level up to elevations of¢. 2000 m.

Food and Feeding. The Riparian Myotis forages in forested areas and over water. Its diet includes a large variety of insects, particularly Coleoptera, Diptera, Lepidoptera, and Orthoptera, caught in flight.

Breeding. In Costa Rica, the Riparian Myotis is considered seasonal monoestrous, with high prevalence of pregnant females in April-June. Pregnant females were observed in August in Peru. Birth of one young was observed in November in Uruguay. One pregnant female, with one embryo of 7 mm crown-rump length, was collected in February in Panama. Most births seem to be associated with rainy and warm seasons in South American rainforests.

Activity patterns. The Riparian Myotis emerges just before sunset. In rainforest areas in south-eastern Brazil, its activity is concentrated in two periods: first five hours after sunset and last two hours before sunrise. In Argentina, colonies roosted under tree bark of Schinopsis (Anacardiaceae) and in a house roof in a rural area. In Brazil, they were found in caves and crevices in rocky outcrops. Echolocation calls have strongly FM initial components, terminating with short CF components. Mean call parameters in South America are start frequency of 102-7 kHz (98-6-106-4 kHz), end frequency of 61-6 kHz (60-5-63-1 kHz), peak frequency of 66-6 kHz (64-4-70-2 kHz), bandwidth of 41-2 kHz (36-9-44-7 kHz), and duration of 4-4 milliseconds (3:8-5-4 milliseconds).

Movements, Home range and Social organization. Short recapture distances in Costa Rica indicate small home ranges. The Riparian Myotis uses lower forest strata, although it also explores forest canopies. It roosts in colonies of up to 50 individuals and with other bat species such as Common Black Myotis ( M. nigricans), Silver-tipped Myotis ( M. albescens), and Pallas’s Mastiff Bats (Molossus molossus).

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Riparian Myotis is widespread, apparent has large populations with no decline, and occurs in several protected areas.

Bibliography. Arias-Aguilar et al. (2018), Barquez, Mares & Braun (1999), Barquez, Perez et al. (2016c¢), Bernard (2001), Dias & Peracchi (2007), Handley (1960), Kalko & Handley (2001), Kalko et al. (1996), LaVal (1973b), LaVal & Fitch (1977), LaVal & Rodriguez-Herrera (2002), Lépez-Gonzaélez et al. (2001), Moratelli & Morielle-Versute (2007), Moratelli et al. (2013), Novaes, Souza & Moratelli (2017), Simmons (2005), Simmons & Voss (1998), Wilson (2008b).