Western yellow bats (Lasiurus xanthinus) are found in the southwestern region of the United States and northwestern Mexico. In the United States, members of the species live as far north as the southern tip of Nevada, through southern California and the southwest, and as far south as Big Bend National Park, in Texas. Their range continues into Mexico, where western yellow bats inhabit the western peninsula of Baja California and the whole western flank of the Sierra Madre Occidental. Western yellow bats are found throughout central Mexico as far south as Mexico City. Some individual bats are found to be present year-round, while other populations can be migratory. (Dixon, et al., 2004; Higginbotham, et al., 1999; Jones Jr., 1964; Leon-Tapia and Hortelano-Moncada, 2016; O'Farrell, et al., 2004; Stewart, 1969)
Western yellow bats are most commonly found in riparian woodland habitats that include an abundance of trees, including Fremont cottonwood (Populus fremontii), Arizona sycamore tree (Platanus wrightii,), and Arizona white oak (Quercus arizonica). The bats are associated with desert regions in the southwest United States where they occupy thorny, dry environments. They tend to be found in dry tropical forests but can occupy semi-tropical wet forests as well.
Whether it may be a broadleaf deciduous riparian tree in Mexico or a dagger yucca (Yucca gloriosa) in the United States, western yellow bats can hang as low as 2.2 meters from the ground, but will most often occupy the tallest nearby tree. They are found closer to the trunk of palm trees where their fur blends in with the dead fronds.
Western yellow bats are more common in tall trees of at least three meters high and in close proximity to bodies of water, like rivers or ponds. Their capture sites are often in open, grassy areas with water features, but it is unknown whether or not they forage above them. There have also been some reported captures in residential areas and orchards.
There have been no reports on the exact elevational range for these individuals. However, Williams et al. (2006) stated that it is rare for western yellow bats to occupy low elevations in southern Nevada. In the Arizona mountains, these bats can occur up to about 2,000 meters. There have also been mentioned captures at approximately 850 meters. (Higginbotham, et al., 1999; Leon-Tapia and Hortelano-Moncada, 2016; Ortiz and Barrows, 2014; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015; Williams, et al., 2006)
Western yellow bats have pale yellow fur with a light brown tint around their eyes. A dark ring outlines their relatively short ears. As their name suggests, these bats have a bright yellow color on the anterior half of their uropatagium (or tail membrane), while the posterior half is nearly hairless. This contrasts the color of their upper back. Older individuals may have small white and gray patches of fur. Although members of the genus are born furless, juveniles appear relatively similar to adult western yellow bats, with a well-furred yellow pelage. Weights at birth and growth rates have not been reported.
Western yellow bats typically have a mass of 9.2 to 22.5 g, a wingspan of about 33.5 to 35.5 cm, and length of around 100.7 to 110.6 mm. These measurements can vary depending on the location. In Mexico, these bats tend to be around 10 to 15 g. In Texas, there have been captures of adult males with masses between 12 and 19 grams.
Western yellow bats are sexually dimorphic, with females typically larger than males. Males have an average total length of 106.6 mm, forearm length of 43.3 mm, hind foot length of 10.6 mm, ear length of 13.1 mm, and weight of 12 g. Females have an average forearm length of 45 mm, hind foot length of 10.4 mm, ear length of 14.5 mm, and a weight of 19 g. The upper-jaw tooth row of female western yellow bats ranges from 5.5 to 5.9 mm. The dental formula of western yellow bats is i 1/3, c 1/1, p 1/2, m 3/3, and they possess a total of 30 teeth.
Western yellow bats are similar to southern yellow bats (Lasiurus ega). Both have golden brown face masks, and short, triangular ears. However, southern yellow bats have a face mask that is a noticeably darker brown than western yellow bats. Southern yellow bats also lack the darker ring around their outer ears, a feature which western yellow bats possess. (Arroyo-Cabrales and Alvarez-Castaneda, 2017; Higginbotham, et al., 1999; O'Farrell, et al., 2004; Rainey and Brown, 2018; Stewart, 1969; Tipps, et al., 2011; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015)
Western yellow bats mate in the fall. After mating, the bats part ways and the females store the males' sperm. The duration in which females store sperm can vary, therefore the breeding season is unknown. Males and females will mate with multiple partners and are considered polygynandrous. Ortiz and Barrows (2014) report that male Lasiurus bats can secrete a thick and oily pheromone, which produces a strong odor. This pheromone is thought to be secreted from underneath their wings, with the purpose of attracting females during flight. Their ears also help them hear and sense their surroundings, including potential mates. (Ammerman and Citlally, 2015; Arroyo-Cabrales and Alvarez-Castaneda, 2017; Higginbotham, et al., 1999; Lacki, et al., 2007; O'Farrell, et al., 2004; Ortiz and Barrows, 2014; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015)
Western yellow bats are iteroparous, breeding once yearly. The males and females will mate in the fall, but females will hold on to the sperm for an indefinite amount of time. O'Farrell et al. (2004) state that females are pregnant between April and June, but the duration in which they store the sperm is not yet determined. Shump (1982) and Pierson et al. (1998) recorded that other species in the Lasiurus genus are typically pregnant for about 90 days, but the gestation period of western yellow bats is unknown. Females typically give birth in une and July. Two pups are usually born, but the size of the litter can vary from two to four pups. Embryo size can vary from about 13 to 17 mm by the end of the pregnancy. The birth size has not been recorded but pups from other Lasiurus species range from about 2.5 to 5 g. A specific age at which western yellow bats are sexually or reproductively mature has not yet been recorded, but it is predicted that both sexes are mature within their first year. (Ammerman and Citlally, 2015; Higginbotham, et al., 1999; O'Farrell, et al., 2004; Ortiz and Barrows, 2014; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015)
Males breed with females but do not have a parental role or further investment. While pregnant, females protect and care for their pups. The weaning period for L. xanthinus is typically around a month, and pups begin to fly after about three to four weeks. Once they learn how to fly, western yellow bats will typically stay with their mothers for a couple more weeks until they are fully capable of flying, foraging, and roosting by themselves. Their average time to independence is approximately 1.5 months. When offspring are very young, scent and echolocation are important, as mothers use it to communicate with pups if separated. (Ammerman and Citlally, 2015; Higginbotham, et al., 1999; O'Farrell, et al., 2004; Ortiz and Barrows, 2014; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015)
There are no sources that provide a published lifespan range for western yellow bats in the wild. Because these bats are not kept in captivity, there is no reported lifespan for captive members.
However, members of the genus Lasiurus have been reported to live for an average of 14 years in the wild. It is expected that western yellow bats have a similar lifespan to others in their genus. (Arroyo-Cabrales and Alvarez-Castaneda, 2017)
Western yellow bats are active year-round, suggesting that they do not hibernate. They are typically solitary tree-roosters, tending not to form clusters. There have been no confirmed colonies in human-occupied buildings and, although individual bats may accidentally fly indoors. They do exhibit a year-round residence and aggregate in breeding colonies once a year.
These bats are migratory and tend to move south in winter, when insects they feed on become scarcer. In Colorado, O'Farrell et al. (2004) hypothesized that the individuals that migrate southward probably take routes along muddy rivers. Areas with scattered palms and patches of trees would best provide them with viable foraging locations during their travels. They migrate northwards around April, when the weather gets warmer.
Western yellow bats are fully nocturnal during the summer and moderately nocturnal during the spring and fall months. In the winter these bats can be found either migrating to warmer climes, or remaining in colder regions and being less active. Western yellow bats can be active during the daytime in winter if the insects they eat are still available.
Pregnant females are more active from April to June. Lactation behaviors in females typically occur the first two weeks after birth. In northern states, males appear to be scarcer between April and June as parturition occurs and both sexes do not interact with each other. At this time, Lasiurus pregnant and lactating female bats form maternity colonies. The reason for this is undetermined.
Western yellow bats perceive their surroundings through vision during daylight hours and echolocation at night. They both communicate and navigate their environment using echolocation. (Higginbotham, et al., 1999; Higginbotham, et al., 2000; Jones Jr., 1964; O'Farrell, et al., 2004; Ortiz and Barrows, 2014; Rainey and Brown, 2018)
An area has not been specifically identified for the members of this species. Western yellow bats are not known to actively defend a territory. (Ortiz and Barrows, 2014; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015)
Western yellow bats, like other bat species, use both smell and hearing to communicate and perceive rather than just acoustic communication. Their eyesight is just as capable as that of humans during the daytime. Although they have good vision, they rely heavily on senses other than just eyesight to communicate socially. Mothers and pups use scent to find one another and touch as the pup feeds on milk. Touch is also necessary when mating.
Western yellow bats interpret chemical cues to determine what is around them and what they are about to eat. They also use their hearing to listen to calls from other bats and avoid collisions. Wester yellow bats utilize echolocation to forage, navigate, and communicate with other bats. O’Farrell et al. (2006) documented that western yellow bats have a higher frequency than other tree-roosting bats. In the genus Lasiurus, calls can begin as high as 60 kHz and can end as low as 32 kHz. There are some variations in call sequences and frequencies, but their average echolocation frequency is about 50 kHz.
Some other bat species secrete chemicals from their interaural (inner-ear) gland to provide information about themselves and their colony, but no recent studies have confirmed this for western yellow bats. (Higginbotham, et al., 2000; Jones Jr., 1964)
Western yellow bats are insectivores, and it has been suggested that they primarily consume beetles (order Coleoptera). Through observation, it is believed that juvenile bats consume ichneumonids (order Hymenoptera). Fecal analysis from one individual bat in Texas included insects from a diverse set of orders: Hemiptera (true bugs), Diptera (true flies), Hymenoptera (ants, bees, sawflies), Lepidoptera (moths), Coleoptera (beetles), and Orthoptera (grasshoppers).
Western yellow bat pups depend on their mothers for nourishment until they are able to fly. (Higginbotham, et al., 1999; O'Farrell, et al., 2004; Rainey and Brown, 2018; Zabriskie, et al., 2019)
Western yellow bats have known predators that include barn owls (Tyto alba), domestic dogs (Canis lupus familiaris), and domestic/feral cats (Felis catus). Other similar roosting bats have predators like roadrunners (Geococcyx californianus). Raccoons (Procyon lotor) have been found disturbing tree-roosting bat species but do not directly harm them. Raccoons and roadrunners disturb other bat species with similar behaviors to western yellow bats, making researchers believe that they can potentially be harmful to western yellow bats as well.
L. xanthinus have yellow-brown fur that helps them stay camouflaged when hanging in trees. Their hearing and sense of vibration helps them listen for potential predators. (Ortiz and Barrows, 2014; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015)
Lacki et al. (2007) explain that western yellow bats play an essential ecological role in their riparian woodland habitats as they eat beetles (Order Coleoptera) and moths (Order Lepidoptera). Predators like barn owls (Tyto alba), domestic dogs (Canis lupus familiaris) and domestic/feral cats (Felis catus) eat them.
Parasite studies are minimal for western yellow bats. A single individual in Arizona was tested for multiple parasites associated with tick-borne diseases, but the results were negative. Bradshaw and Ross (1961) suggest that these bats could potentially host species of soft ticks in the genus Ornithodoros (e.g. Carios stageri and Ornithodoros rossi). (Bradshaw and Ross, 1961; Lacki, et al., 2007; O'Farrell, et al., 2004; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015; Zabriskie, et al., 2019)
Ortiz and Barrows (2014) assert that ecotourists in the United States go hiking with the intention of finding unique bat species such as western yellow bats.
It is thought that these bats eat and reduce insect communities, including in human-occupied environments. However, there is no specific evidence that confirms that western yellow bats control any particular species or species group. (O'Farrell, et al., 2004; Ortiz and Barrows, 2014)
There is an inconvenience presented by these bats when they inhabit attics and other human habitations. Efforts to remove bats from homes can be expensive.
Western yellow bats are known to carry rabies, providing another negative economic impact on human health.
In Arizona, one individual was tested for tick-borne pathogens. Although the examined individual tested negative, the results suggest that these bats could host tick species that can negatively affect humans. (Ortiz and Barrows, 2014; Pierson and Rainey, 1998; Venters, et al., 1954; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015)
Western yellow bats are listed on the IUCN Red List as species of "Least Concern." They have no special status on the US Federal List, CITES, and State of Michigan List.
There have been few recognized threats to the survival of western yellow bats. In the United States, cosmetic trimming of palm fronds is the primary threat to these bats. Trimming fronds affects their habitat and can harm their roosting sites. Using excessive amounts of pesticides can also be a reason for decline, unnaturally decreasing insect communities on which these bats feed. In Mexico, humans have not been found directly killing western yellow bats, but they set up barbed wire fences and burn down forests that disturb their habitat. Even with these potential threatening actions, the bats currently maintain stable populations.
With currently stable populations for these bats, not many conservation efforts have been put in place. Although they are not threatened, minimizing direct or indirect habitat destruction remains a viable conservation measure. Western yellow bats may also benefit from reduced pesticide use and the planting of ornamental palm fronds. An unintentional conservation measure may include maintaining bat foraging corridors. Ortiz and Barrows (2014) found that occupancy patterns of western yellow bats were highest when foraging corridors were defined and protected, suggesting that such corridors may be a viable conservation measure. (Ammerman and Citlally, 2015; Arnett, et al., 2016; Arroyo-Cabrales and Alvarez-Castaneda, 2017; Lacki, et al., 2007; Ortiz and Barrows, 2014; Pierson and Rainey, 1998; "Western Yellow Bat (Lasiurus xanthinus) (WYBA) Basic Conceptual Ecological Model for the Lower Colorado River", 2015)
Emily Cardoso (author), Radford University, Lauren Burroughs (editor), Radford University, Logan Platt (editor), Radford University, Karen Powers (editor), Radford University, Galen Burrell (editor), Special Projects.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
An animal that eats mainly insects or spiders.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
reproduction that includes combining the genetic contribution of two individuals, a male and a female
mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
uses sound above the range of human hearing for either navigation or communication or both
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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