The Yuma myotis (Myotis yumanensis) is one of the smaller members of the family Vespertilionidae, and one of several Myotis bats found in the Park Service's Mojave Desert Network parks: Joshua Tree National Park, Lake Mead National Recreation Area and Mojave National Preserve. This profile draws on a piece by Scientists in Parks intern Sofia Elizarraras.
At a glance
| Body length | 1.5–1.9 inches |
| Weight | Under half an ounce |
| Wingspan | About 9.4 inches (23.9 cm) on average |
| Fur | Dark to light brown above, pale brown below; glossy dark brown ears |
| Named for | Fort Yuma, California, across the Colorado River from Yuma, Arizona, where it was first recorded in 1864 |
| Lifespan | About 8 years in captivity, sometimes over 10; one captured male was documented at 14 |
| Conservation status | "Least concern" (IUCN); listed as of special concern by some states |
Where it lives
Though first found on the Arizona–California border, the Yuma myotis ranges across western North America, from southwestern Canada into Mexico, in forests, streamside zones, deserts and grasslands. Water is the constant: it hunts best over rivers, streams and lakes.
It prefers to roost in buildings and bridges, but also uses caves and abandoned mines, in colonies of up to 10,000. Bachelor males sometimes move into old swallow nests.
It likes warmth and hibernates through winter in cool caves and crevices. Its hibernation is little studied, but it probably spends part of the time in torpor — lowered activity, body temperature and metabolism — and likely does not migrate far. At Lake Mead, it has been recorded flying on warmer winter nights.
How it lives
- Hunting. It comes out at dark and finds insects by echolocation, bouncing moderate-length calls off its prey. Its wings are wide for its size, making it very agile.
- Diet. It feeds mostly over water on whatever insects are plentiful — moths, beetles, mosquitoes, midges and flies.
- Breeding. Mating happens in autumn, and the species is polygynandrous: males and females each mate with several partners. Reproduction takes place between spring and summer, with each female bearing a single pup in maternity colonies that can hold several thousand bats. Because they breed slowly, healthy populations are crucial.
The threats
Habitat loss. Hotter, drier conditions shrink the pools the bats drink from and the insect swarms they feed on around water.
White-nose syndrome (WNS). This fungal disease has spread across the country since 2006, killing 90–100% of some bat populations. The fungus, Pseudogymnoascus destructans (Pd), leaves a powdery white coating on the muzzle and can damage the wing tissue bats need to fly. Infected bats wake from hibernation too often or too early and fly out into freezing weather with little or no food to find.
A bat with the white fungal growth of white-nose syndrome around its nose. NPS / von Linden.
The Yuma myotis was among the first western species confirmed with WNS, when dead bats were found in Washington State in 2017. Myotis bats are especially vulnerable, and cave-dwelling species most of all, since caves are where most bats pick up the disease.
What the Park Service is doing
Setting a mist net to capture and monitor bats in Parashant National Monument. Credit: National Park Service.
- Monitoring. The Mojave Desert Inventory and Monitoring Network tracks bat abundance and diversity across its parks and swabs bats once a year for the WNS fungus. WNS has not been found in Nevada, California or Arizona, where it monitors, but Pd is presumed present in its parks, based on low levels of fungal DNA possibly detected in 2021. Elsewhere, the disease has appeared one to several years after the fungus was found, so monitoring continues.
- Closures. Park managers may close caves or areas to protect hibernating bats.
- Decontamination. Some parks require visitors to clean their shoes entering and leaving cave tours.
- Education. Interpreters and science communicators teach visitors about WNS and protecting bat habitat.
Why bats matter
WNS is not known to infect people, but losing bats still affects us. Bats are a leading natural pest control — all those mosquitoes eaten mean fewer bites for campers — worth an estimated $3.7 billion to $53 billion a year in the United States. Many bat species are also important pollinators.
A bat's flight traced against the Milky Way at Johnson Lake, Great Basin National Park. NPS / Gretchen Baker.
Sources
Based on "Yuma Myotis Bat," by Scientists in Parks intern Sofia Elizarraras, Mojave Desert Inventory and Monitoring Network, published by the National Park Service; rewritten in hubnx's own words.
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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