Rediscovering the Western Mastiff Bat
A bat struggling to survive in Los Angeles
Western Mastiff Bats in Los Angeles
The western mastiff (Eumops perotis) bat has been a long time beneficial resident of Southern California, with research on this bat dating back to the early 1900s. This bat is the largest in North America and has a wingspan of up to 2 feet. Due to its large size and narrow wing to body ratio, it requires a high roost in order to achieve flight, making it rely on long bodies of water to drink from and high structures to call home. As a result of urbanization, western mastiff bats have been displaced from their typical cliffside or tree habitats into man-made structures such as houses and bridges.
At one time, they were found locally in colonies of up to 70 bats, but not long ago, they were thought to have been eradicated from the Los Angeles basin, with remnant populations only surviving in bordering open spaces such as the western Santa Monica Mountains. These bats were rediscovered in 2012 at the Los Angeles Zoo in Griffith Park by biologists Ted Weller and Miguel Ordenana via a US Forest Service acoustic monitoring project. At that time, scientists feared that Griffith Park was the extent of the western mastiff bats' range within LA’s urban core.
Thanks to research conducted by The Backyard Bats program at the Natural History Museum of Los Angeles (NHMLA), it was discovered that the mastiff bat is still present in the Los Angeles basin. The map below shows sightings of the mastiff in the 1900s, compared to modern-day sightings from NHMLA's Backyard Bats partnership with community scientists..
Why are the mastiff bats disappearing?
There are many factors that have contributed to the decline of the mastiff population including: urbanization, loss of drinking sites, wide use of pesticides and other human activities including deliberate eradication, that have played a role in the reduced numbers of the western mastiff. When their natural roosts were removed to build human structures, the mastiffs adapted and found new homes in buildings and bridges. Despite their resilience and attempt to adapt to these changes, they continued to be persecuted and killed.
"Previously, the bats had occupied the attic, but their noise was such a nuisance that the ventilators were covered with netting and the twenty or thirty bats thus imprisoned were caught and killed." — A. Brazier Howell
Multiple bat species are native to Los Angeles, and play a vital role to the natural ecology and balance in our environment. Bats act as natural pest control, as their primary source of nutrition is feeding on insects. Unlike other bat species with thriving local populations, like the Mexican free-tailed (Tadarida brasiliensis) bat (see map below), the mastiff bat is struggling to survive in Los Angeles.
Sightings of Mexican free-tailed bats
How can I support my local bats?
NHMLAC and FOLAR conducting an educational bat river walk at the Brews and Bats event.
Although all bats deserve our attention and conservation efforts, the mastiff needs to be further researched and conservation efforts increased if Los Angeles wants to see this native bat return to its former glory.
The Backyard Bats Survey , led by Miguel Ordeñana at the Natural History Museum of Los Angeles County, tracks bats across Los Angeles. Acoustic sensors in understudied neighborhoods collect data on bat activity, allowing scientists like Miguel to understand bat populations in urban areas. The maps in this story were created using the data from Backyard Bats Survey sensors.
You can volunteer to host a sensor in your own backyard or just attend one of the many events that the Backyard Bats team hosts throughout the year, such as their Roost Counts in the summer or the Bats and Brews events held in collaboration with Friends of the L.A River (FOLAR). Becoming informed and learning more about bats is the first step in helping conserve our bat population.