Townsend’s Big-eared Bat
Species: Townsend’s Big-eared Bat – Corynorhinus townsendii
B.C. Status: Blue
The Townsend’s big-eared bat is also commonly known as the lump-nosed bat. Their ears and their nose are two defining features that can help to identify this species. With ears half the size of their body, they use echo-location to detect flying insects. Once they find their prey, they shut down their sonar so they become silent to their prey. Their nose is able to emit echolocation pulses almost as well as their mouths. The big-eared bats’ diet consists of 80% moths, and other small, flying, nocturnal insects.
These bats are year-round residents in the Pacific Northwest. In winter they hibernate in colonies typically in caves, abandoned mines, or cliffs. Their hibernation site needs almost complete darkness, some air movement, consistent temperature, and humidity. This is where Townsend’s big-eared bats mate, and where they rest until coming season when the insects are flying again.
Once spring emerges, so do they. The females form maternity colonies usually in a new site where they raise their young, while the males become solitary during the warmer seasons. Their roosts can be found in large trees, cliffs and buildings. These bats do not hide in crevices as do other bats, so this does make them more susceptible to humans’ activity.
If disturbed, the entire colony will leave their site to find another. This of course is incredibly energy intensive and if disturbance happens, especially in the winter or while they are raising their young, this can severely impact the survivability of the mothers and their young. On top of protecting the colony itself, it is also wise to avoid proximity to bat colonies because there are human health risks involved in getting too close; they are hosts of bacteria and parasites.
Despite their sociability, their colony sizes are relatively small compared to other bat species. In British Columbia, 16 hibernation sites have been discovered, and from data collected only 350 bats have been documented. The total known winter population is less than 100 bats. Of course, there likely are some sites that haven’t been discovered, but the population is very small – keep in mind that females reproduce only one young per year.
There are certain contributing factors which explain why their population numbers are so small and at risk. They are dependent upon insect populations and the land use near bat colonies can negatively affect them, such as, use of insecticide.
Disturbance is another huge risk to the big-eared bat population, as it effects the entire colony and effects survivability of young. Many of their roosting sites are not protected from human disturbance and when one site is affected, an entire colony is affected. Demolition of mines and deforestation are two major human activities that are directly impacting their habitat and foraging grounds. On the gulf islands, no maternity sites have been found, and nursery sites remain unknown. If you see any evidence of these bats, please report them to us!
Although no reports have been discovered for this particular species, White-nose syndrome, a fungal disease which has killed millions of bats in North America, thrives best in cold humid conditions typically found at the hibernation site of these bats and is a potential threat. This disease is more common in the east, but it is spreading across to the west. The big-eared bat is a species of concern.
Identification – what to look for?
- Huge ears, measuring about half of it’s body length (pointed forward while in flight)
- Dull brown to grayish fur colour
- Medium size species – wingspan around 30 cm in length
- Body length around 10 cm
- Short snout with long nostril slits
Where are they found?
- Year-round residents only in North America – from the Rockies to southern Mexico to southern B.C.
- Coniferous forests, montane ecosystems
- Places where there are warm and dry summers and not an extremely cold winters
- Caves, mines, large trees, cliffs
- In the summer months, they can and may live in buildings
- Often found foraging around moist ecosystems and wetlands
- As night-flyers they can be found among the shrubs and trees of the forests
- Bats are the only mammals that have evolved to truly fly
- Bats inhabit all continents except for Antarctica
- Townsend’s big-eared bats can live for up to 21 years! Mortality rate in young is high but decreases as they age
- In hibernation, their body temperature drops to around the same as the cave and their heart rate drops from 100 to 5 beats per minute! Indeed, it is important to leave them undisturbed especially in this time
- They are fairly sedentary species – their year-round range is within 20 to 30 km
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