Smaller Vespertilionid Bats
Y – Canyon Bat (Parastrellus hesperus)
Key features: Smallest North American bat (body length: 60-70mm); forearm 25-30mm; dark facial mask; unique (blunt) tragus (unlike Myotis); keeled calcar; one tiny premolar – Myotis have two – however, this is an in-hand trait only.
Y – Little Brown Bat (Myotis lucifugus)
Key features: Rare in SLO, MON, and SBA counties. Small bat; body length 80-95mm; forearm length 36-40mm; wingspan 220-270mm; fur darker on dorsum than ventrum; feet w/long toe hairs that extend to tips of toes.
Y – Fringed (fringe-tailed) Myotis (Myotis thysanodes)
Key features: Body length 75-105mm; relatively long ears (16-20mm); often with notable facial mask; only Myotis w/fringe of (stiff) hairs along edge of interfemoral membrane.
Y – Long-legged Myotis (Myotis volans)
Key features: Body length 95-103mm; forearm 36-42mm; underwing furred near body from knee to elbow; obvious keel on calcar.
Y – Long-eared Myotis (Myotis evotis)
Key features: Body length 75-95mm; forearm 36-41mm; extremely long ears for a Myotis (18-25mm); also, ears black, shiny, and hairless.
Y – California Myotis (Myotis californicus)
Key features: All-around small bat – body length 65-90mm; forearm 32-38mm; base of hairs typically much darker than tips; foot is very small (5-8mm); forearm is small (< 35mm); calcar is keeled.
Y – Small-footed Myotis (Myotis ciliolabrum; IUCN considers the western race a distinct species, M. melanorhinus (the “dark-nosed small-footed myotis”). There is little consensus for this designation)
Key features: Rare or absent along coast. Similar to California myotis: Small size (body length 65-85mm); forearm 30-35mm; foot similarly small (5-8 mm), calcar is keeled; dorsal surface of interfemoral membrane furred on anterior half; skull flattened; ears black; typically has distinctive black facial mask.
Y – Yuma Myotis (Myotis yumanensis)
Key features: Noticeably two-toned (darker on back, lighter on underside); small bat (body length 85-90mm); forearm 32-36mm; large feet (≈10 mm); short ears (13-15mm), lacks keel on the calcar.
Y – Western Big-eared Bat (Corynorhinus townsendii pallescens)
Key features: Just slightly larger than large Myotis species (body length 90-115mm); forearm 39-44mm; large ears (30-40mm); distinct horseshoe-shaped lump on nose.
Molossid (free-tailed) Bats
Y – Mexican (Brazilian) Free-tailed Bat (Tadarida brasiliensis)
Key features: A small bat (body length 90-105mm) with long narrow wings (extremely fast flier); forearm 36-46mm; tail extends out from the interfemoral membrane; long hairs extend from toes; unlike mastiff bat, ears don’t meet in the middle of forehead; notably wrinkled lips.
Y – Western Mastiff Bat (Eumops perotis)
Key features: Rare in SLO, MON, and SBA counties. Largest U.S. bat; body length 140-185mm; forearm 72-82mm; long, narrow wings; approx. half of tail is free from the membrane between hind legs; large ears join at the midline of forehead, noticeable underbite.