A Key to the Bats


1a. Interfemoral membrane lightly furred; fur uniformly black but many of the hairs are distinctly silver tipped, especially on dorsum; and face NOT distinctly lighter than back, then

Lasionycteris noctivagans – Silver haired Bat

1b. If fur not as above; fur variously colored, go to #2

2a. Tail extending (usu.>30mm) beyond edge of interfemoral membrane, go to #3

2b. If no extension of tail beyond edge of interfemoral membrane, go to #4

3a. If forearm more than 70mm, then

Eumops perotis – Western Mastiff Bat

 3b. If forearm less than 55mm, then

 Tadarida brasiliensis – Mexican Free-tailed Bat

4a. If ears more than 20mm in height from notch to crown, go to #5

4b. If ears less than 20mm in height from notch to crown, go to #6

5a. If ears widely separated; hair yellow next to skin; forearm (radius) more than 46mm; and large-eyed, then

Antrozous pallidus – Pallid Bat

5b. If ears close together at anterior base, hair dark gray next to skin, and forearm less than 46mm, then

Corynorhinus townsendii pallescens – Townsend’s Big-Eared Bat

6a. Upper surface of interfemoral membrane bare, or if slightly furred, hairs of back not tipped with white, go to #8

6b. Upper surface of interfemoral membrane densely furred, go to #7

7a. Forearm more than 45 mm; silver-tips on some hairs, then

Aeorestes cinereus – Hoary Bat

7b. Forearm less than 45mm, brick red fur, then

Lasiurus frantzii – Western Red Bat

8a. First visible tooth behind upper canine about 1/2 as high as the canine and in contact with it at base, go to #9

8b. First visible tooth behind the upper canine less than 1/3 as high as canine, or if 1/2 as high, then separated from the canine by a noticeable gap, go to #10

9a. Forearm more than 40 mm; tragus pointed, then

Eptesicus fuscus – Big Brown Bat

9b. Forearm less than 40 mm; tragus < 5 mm, blunt, and club-shaped, then

Parastrellus hesperus – Canyon Bat

10a. Dorsal surface of interfemoral membrane only furred on anterior half; foot <8 mm; dorsal fur glossy; wings and tail membrane black

Myotis ciliolabrum – Small Footed-Myotis

10b. Dorsal anterior surface of interfemoral membrane without dense fur, foot > 8.5 mm, go to #11

11a. Ear when laid forward extending > 2 mm beyond tip of nose; ear more than 16mm from notch to tip, go to #12

11b. Ear when laid forward extending < 2 mm beyond tip of nose; ear less than 16mm, go to #13

12a. With a fringe of stiff hairs on posterior edge of the interfemoral membrane, then

Myotis thysanodes – Fringed Myotis

12b. Without a conspicuous fringe of hairs on edge of interfemoral membrane; ears pitch black, opaque, 20-25mm, then

Myotis evotis – Long-eared Myotis

 13a. Calcar with distinctive keel, go to #15

 13b. Calcar without keel, go to #14

 14a. Skull < 14 mm, total length, fur w/dull luster; body two-toned (darker on back, lighter on underside), then

 Myotis yumanensis – Yuma Myotis

 14b. Skull > 14 mm; fur usually glossy, then

 Myotis lucifugus – Little Brown Myotis

 15a. Forearm 37 mm or more, then

Myotis volans – Long-legged Myotis

15b. Forearm 35 mm or less, then

Myotis californicus – California Myotis