Western Yellow Bat (Lasiurus xanthinus)

Protection Status Notes
Based on recent records from west Texas and Nevada, L. xanthinus seems to expand its range to the east and north. It was speculated that global warming might play a role. However, since southwestern yellow bats have not been studied, their status remains unknown.
L. xanthinus and L. ega cannot reliably be distinguished from each other morphologically, but their ranges do not overlap. Yellow bats can be distinguished from other bat species by the combination of yellow coloration, size (forearm = 45‑50 mm), and short ears.
Life History
Some populations may be migratory, although some individuals appear to be present year-round, even in the northernmost portion of the range. Western yellow bats probably do not hibernate; activity has been observed year‑round in both the southern and northern portions of the range. Capture sites are often associated with water features (e.g. stock tanks, ponds, streams, and rivers) in open grassy areas and scrub, as well as canyon and riparian situations. Captures are also reported over swimming pools, lawns in residential areas, and orchards. In northern areas, seasonal segregation between the sexes during parturition may occur, as males are scarce from April through June. In the U.S., pregnant females are known from late April through June, with lactation occurring during June and July. The number of embryos carried by pregnant females varies from one to four, with no apparent geographic trend. Reported predators include barn owls, domestic dogs and domestic cats.

Yellow bats are insectivorous. Very limited diet data from Mexico suggest the primary prey is beetles, but no information is available from the southwestern United Sates.
Western yellow bats are thought to be noncolonial. Individuals usually roost in trees, hanging from the underside of a leaf. They are commonly found in the southwestern U.S. roosting in the skirt of dead fronds in both native and non‑native palm trees.
Recent genetic work argues strongly that the southern yellow bat, formerly considered to be Lasiurus ega, should be considered two distinct species, Lasiurus ega and Lasiurus xanthinus. The western yellow bat has a primarily Mexican and Central American distribution, but extends into the southern portions of California, Arizona, and New Mexico, and into the western portion of Texas. Western yellow bats are associated with dry, thorny vegetation on the Mexican Plateau, and are found in desert regions of the southwestern United States, where they show a particular association with palms. They are known to occur in a number of palm oases' but are also believed to be expanding their range with the increased usage of ornamental palms in landscaping. L. xanthinus occurs up to ca. 6500 feet in the mountains in Arizona.
Threats and Reasons for Decline
Few threats to the survival of yellow bats have been reported. Probably one of the primary threats in the U.S., however, is the cosmetic trimming of palm fronds. The use of pesticides in date palm and other orchards may also constitute a threat to both roosting bats and the insects upon which they forage. Domestic cats, whether pets or feral, may be a significant source of predation, as they are for many lizards, songbirds, and rodents.
Ongoing Recovery
Since western yellow bats have not been studied, their status, conservation, and management needs remain unknown. It has been speculated that widespread introduction of California and Mexican fan palms as ornamentals may have provided here-to-for unavailable roosts in Southern California.
The following areas need more investigation to accurately determine the status of and conserve the Western yellow bat in the U.S.: distribution, migration habitat requirements, activity patterns (both daily and seasonally), and threats including palm frond trimming and pesticide use in orchards.