Key Identification Features and Natural Histories of California Myotis and Yuma Myotis
Maggie Shirley
May 1, 2018
NRM 3202 – Wildlife Identification & Natural History
Introduction
It can be difficult for the layman to tell the differences between the California Myotis bat (Myotis californicus) and the Yuma Myotis bat (Myotis yumanensis). The purpose of this document is to detail the visible differences used to distinguish between the two species, and to provide general natural history information for each.
California Myotis bat (Myotis californicus)
Description
This bat is reddish-brown to goldish-brown, with a dark face. It is relatively small within the myotis genus (average weight ~3-5 g). Only the tip of the tail extends beyond the uropatagium between the legs. There is no distinct sexual dimorphism, however females are, on average, larger than males. Young are born blind and hairless, but resemble adults within two weeks. Ears extend beyond the nose when pushed forward.
Distribution
Occurs widely along the Pacific coast and within the American southwest.
Diet
They are insectivores, foraging for flying insects 2 to 3 meters above ground.
Habitat
These bats are associated with oak woodlands along the Pacific coast and pinion-juniper communities of the deserts. They prefer lower elevations and are not common in mountainous conifer forest.
Reproduction
Mating happens in the fall, but females retain sperm for several months, so that ovulation and fertilization do not immediately occur. Early in the summer, a female joins a maternity colony where she gives birth to one offspring, between late May to early July.
Other Habits
Roosts in buildings, caves, and mine shafts. Somewhat solitary, roost alone or in small groups.
Of Interest
Recovery of banded individuals reveals that this species may live up to 15 years in the wild. White-nose syndrome was detected in this species in 2007.
California Myotis bat (Myotis californicus)
Yuma Myotis bat (Myotis yumanensis)
Description
This bat is gray, tan, or brown; it is relatively small within the myotis genus (average weight ~6 g). Only the tip of the tail extends beyond the uropatagium between the legs. There is no sexual dimorphism. Young are born blind and hairless, but resemble adults within two weeks.
Distribution
Occurs widely throughout California, Oregon, and Washington. Its range extends from British Columbia to the north, central Mexico (including Baja California) to the south, and Texas to the east.
Diet
They are insectivores, foraging for flies, small moths, and beetles over bodies of water.
Habitat
These bats are associated with wooded canyon bottoms and are obligates to riparian areas, hunting for insects over streams and ponds.
Reproduction
Mating occurs in the fall, but females retain sperm for several months, so that ovulation and fertilization do not immediately occur. Early in the summer, a female joins a maternity colony where she gives birth to one pup, between late May to early July.
Other Habits
They will use tail membranes to snare prey that is too large for their mouths. They are social; roost in colonies year around.
Of Interest
In May of 2017, white-nose syndrome was recorded for the first time in this species, in Washington state.
Yuma Myotis bat (Myotis yumanensis)
Differentiating California Myotis from Yuma Myotis
Because obvious morphological features, such as fur coat color, can be variable in both of these species, specific measurements are the most reliable way to differentiate them. Foot length and forearm length are the most reliable morphological features to identify between these bats.
Search call identification
An important key identifying feature of bats is actually something you cannot detect using human senses, ultrasonic calls. Bats emit calls in a 12,000 Hz to 160,000 Hz frequency range, whereas humans can only hear within the 20 to 20,000 Hz frequency range. With the help of a relatively simple device that converts echolocation ultrasound signals to audible frequencies, these calls can be used to identify bats.
All bats will use different types of calls for a given activity, such as search calls, feeding buzz, social calls, etc. Search calls are used for general navigation and searching the landscape; these calls are considered ‘diagnostic’ meaning species search calls are clearly distinguishable from one another.