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1. Fur uniformly black, and many of the
hairs are distinctly silver-tipped, especially on dorsal
(back) surface...........................Lasionycteris
noctivagans
Silver haired Bat
1a. Not as above; fur variously colored..................................................................2
2. Tail extending conspicuously (more than
30 mm) beyond edge of interfemoral membrane (membrage
stretching between tail and hindlegs) .................................................3
2a. No extension of tail beyond edge of interfemoral membrane.....................................4.
3. Forearm more
than 70 mm. ..................Eumops
perotis Western
Mastiff Bat
3a. Forearm less than 55 mm. .......Tadarida
brasiliensis Mexican
Free-tailed Bat
4. Ears more than 20 mm in height from notch to crown
.
....................................5
4a. Ears less than 20 mm in height from notch to crown .............................
.............6
5. Ears widely separated; hair yellow next to skin, forearm
(radius) more than 46 mm .......................................................Antrozous
pallidus Pallid Bat
5a. Ears close together at anterior base; hair plumbeous (blackish
gray) next to skin: Forearm less than 46 mm. ........................Plecotus
townsendi
Townsend's Big-Eared Bat
6. Upper surface of interfemoral membrane bare, or if slightly
furred, hairs of back not tipped with white....................................................................................................9
6a. Upper surface of interfemoral membrane densely furred
............
8
8. Forearm more than 45 mm, silver-tips
on some hairs...Lasiurus
cinereus
Hoary Bat
8a. Forearm less than 45mm, brick red fur....................Lasiurus
blossvillii
Red Bat
9. First visible tooth behind upper canine about 1/2 as high
as the canine and in contact with it at base (see
diagram-link at right)......................................................................10
9a. 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..............................................11
10. Forearm more than 40 mm, tragus pointed,
.......Eptesicus fuscus
Big Brown Bat
10a. Forearm less than 40 mm, tragus < 5
mm, blunt and club-shaped: ................................Pipistrellis
hesperus Western
Pipistrelle
11. 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
11a Dorsal anterior surface of interfemoral membrane without
dense fur, foot > 8.5 mm .....12
12. Ear when genly laid forward extending > 2 mm beyond
tip of nose; ear more than 16 mm from notch
to tip.....................................................................................13
12a. Ear when gently laid forward, extends < 2 mm beyond tip
of nose; ear less than 16 mm...14
13. With a conspicuous (to naked eye) fring of hairs on posterior
edge of the interfemoral membrane ..........................................
Myotis thysanodes
Fringed Myotis
13a. Without a conspicuous fringe of hairs on edge of interfemoral
membrane, Ears pitch black, opaque,
ears 20-25 mm..............................Myotis
evotis - Long-eared
Myotis
14a. Calcar (spur from heel lying on edge of interfemoral membrane)
with definite keel ..
.16
14. Calcar without keel................................................................................15
15. Skull < 14 mm, total length, fur not brassy-glossy.Myotis
yumanensis -
Yuma Myotis
15a. Skull > 14 mm, fur usually brassy-glossy......Myotis
lucifugus
Little Brown Bat
16. Forearm 37 mm or more. .........................Myotis
volans
Long-legged Myotis
16a. Forearm 35 mm or less.........................Myotis
californicus
California Myotis
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Some definitions
of terms...and links to pictures and drawings that might help.
Notch
in ear = base of tragus (see below).
Forearm:
longest bone in arm, with hook-like thumb at one end.
Total length
= from nose tip to tail tip.
Tragus
= projection surrounded by external ear flap, often stiffened with
cartilage. Ours is a little blunt one, in front, center of ear,
forming front of entrance to ear canal.
Click here to
see diagram of gap behind canine.
Click here to
see "club" shape
of tragus.
Click here to
see diagram of fringe on M. thysanodes.
Click here to
see diagram of keel and calcar on
tail of these bats.
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