Published: June 2013
Author(s): Gerald Hayes and Gary J. Wiles
Bats are the only mammals capable of true flight, and are second only to rodents in the number of species worldwide. They are found on every continent except Antarctica, with 47 species present in the United States. Washington is home to 15 bat species: the big brown bat, California myotis, canyon bat, fringed myotis, hoary bat, Keen's myotis, little brown myotis, long-legged myotis, pallid bat, silver-haired bat, spotted bat, Townsend's big-eared bat, western long-eared myotis, western small-footed myotis, and Yuma myotis.
Bats are the primary vertebrate predators of night flying insects and play an essential role in ecosystem function and human economies. In North America, bats provide an estimated benefit of nearly $4 billion annually to the agricultural industry by preying on agricultural pests. None of the bat species that occur in Washington are listed as endangered or threatened under federal or state law, but two species, Keen's myotis and Townsend's big-eared bat, are classified as state candidate species. They will be reviewed in the future for potential state listing as endangered, threatened or sensitive. Significant information gaps on population status and trends exist for most of the 15 species that occur in the state.
This is the first conservation plan written for the bats of Washington. It summarizes information on the biology and habitat requirements of the species present, discusses factors affecting populations, and outlines conservation activities for maintaining viable bat populations in the state. Brief accounts with background information, photos, and distribution maps are provided for each species.
All 15 bat species in the state have largely insectivorous diets and forage at dusk, night, and dawn. Echolocation is used to capture prey and navigate. All species give birth once per year in the summer, with most having a litter size of one pup. Most species make use of torpor (i.e., the body temperature and metabolic rate are greatly reduced, allowing animals to become inactive during periods of harsh weather and food shortage) during winter hibernation or on a daily basis during other seasons. Two species, the hoary bat and silver-haired bat, are long-distance migrants that overwinter in southern North America, although some silver-haired bats remain in Washington year-round. A number of other species are believed to be short-distance migrants that change elevations as they move to winter roosts with temperatures suitable for hibernation.
The most important habitats for Washington's bats are those used for roosting and foraging. A variety of roost types are occupied to meet daily and seasonal needs, including trees, snags, caves, mines, cliffs, talus, buildings, and bridges. While hoary bats roost almost exclusively in trees, nearly all other bat species in Washington use a variety of roost structures. Some of the state's bat populations make widespread use of cavities and crevices in trees and snags as roosts, with a strong preference for large trees and snags in the early to intermediate stages of decay. Microclimate plays a large role in roost selection, with bats seeking locations having optimal temperatures for saving energy, development of fetuses, and rearing young. Suitable densities of roost sites, especially snags and trees, are important for maintaining viable bat populations.
Adequate foraging habitat is a second primary requirement of bat populations. A number of bat species in Washington concentrate their feeding near fresh water (especially in riparian areas) and along edge habitats, where insect availability is commonly high and vegetational clutter is reduced. Overall activity is typically higher in open sites, including clearcuts, meadows, and forest gaps, than in dense forest. Most of the bat species in Washington make greater use of older, more open forests for foraging than younger forests with denser vegetation. In shrub-steppe and grassland habitats, some bat species favor foraging in riparian zones, while others feed more broadly across both habitats. Availability of drinking sites is another key component of bat foraging habitat, especially in drier regions of the state where water sources may be limited.
Habitat loss and human disturbance are two of the main factors that can negatively impact bat populations in Washington. Habitat loss and alteration affect the availability of both roosting and foraging habitat of bats in the state. Logging and other forest management practices have resulted in younger and often denser forests across the state, causing a general decline in the number of large snags and decadent trees for roosts and also negatively impacting foraging habitat. Regulations requiring the retention of some snags and trees, and buffers around riparian zones have helped reduce this threat, but the issue remains an important concern for forest-dwelling bat species. Agricultural land conversion, urbanization, and mine closures have also reduced roosting and foraging habitat for bats. Human disturbance of bats roosting in caves and other structures is a concern at some sites, but overall is not considered a major threat to most species in the state. Various environmental contaminants also potentially impact some bat populations in the state. Three additional factors (wind energy, disease, and climate change) may increase in importance in the future. Bats are susceptible to being killed at wind energy facilities. Hoary bats and silver-haired bats comprise almost 98% of the bats killed by wind turbines since commercial wind energy production began in Washington in 2001. In 2011, an estimated minimum of 2,419 bats were killed at operational wind projects in the state. Significant expansion of this industry is expected in Washington in the coming decades and even with pre-construction surveys and proper siting, will likely continue to cause mortality to bats. A fungal disease, white-nose syndrome, has recently emerged as a major killer of cave-hibernating bats in eastern North America and is spreading westward. An estimated minimum of 5.7 to 6.7 million bats have died from white-nose syndrome. It is unknown whether the disease will reach Washington or what impacts it may have on bat populations in the state. Species that form tight clusters during hibernation are usually the most vulnerable. Lastly, climate change is likely to alter the future availability of roosting, foraging, and drinking resources for bats, and may have other unforeseen impacts.
The bat conservation plan identifies seven conservation objectives, with strategies and tasks to achieve those objectives. Objectives are:
- Collect baseline inventory data and monitor bat populations to assess trends.
- Safeguard bats from sources of mortality and disturbance.
- Manage habitat to maintain and enhance bat species diversity and abundance.
- Conduct research to determine requirements for bat populations.
- Conduct conservation planning to benefit bats.
- Establish partnerships with agencies, landowners, and other groups to achieve bat conservation.
- Develop and implement public outreach and education programs for bats.
Obtaining basic information on distribution, abundance, and ecological requirements is one of the primary needs for bat conservation in Washington. This information will contribute to an improved understanding of the conservation needs for the 15 species of bats in the state. Addressing threats and maintaining healthy populations of bats will require cooperation and partnerships among government agencies, private resource management entities, non-governmental organizations, tribes, and the public. Partners can also work together to secure funding for implementing priority bat conservation strategies and tasks identified in the plan.
Hayes, G. and G. J. Wiles. 2013. Washington bat conservation plan. Washington Department of Fish and Wildlife, Olympia, Washington. 138+viii pp.