bats taking flight from tree at Yolo Bypass Wildlife Area in Davis California

Bat Migration: Here’s What You Need to Know

California is home to more than 25 species of bats. Whether you are a bat enthusiast or have had bats roosting on your property, you may wonder about the migratory or hibernation behavior of these important pollinators and controllers of insect populations.

Why Do Some Bats Migrate?

Many but not all bat species will head south to destinations like Florida or Mexico’s northern border. Migrating bats do so because of their inability to withstand cold temperatures or because they have the physical size and stamina to fly long distances.

Hoary bats and other species that roost in trees will migrate to warmer climates because trees are simply not warm enough during California winters.

Why Do Some Bats Hibernate?

Some bats hibernate because their location may not provide a year-round supply of insects. In places where the temperature doesn’t drop below 35 degrees, which can be fatal, some bat species must hibernate.

For example, the Little Brown Bats that live in the Sierra Nevada Mountains will spend the winter in caves. In contrast, the Big Brown Bat, found everywhere in North America, is of a relatively large size. This allows it to be more active during winter months, but it’ll hibernate when temperatures drop below 30 degrees Fahrenheit.

Mexican Freetail bats that live in California don’t migrate out-of-state, but will travel to various roosts depending on the season. They prefer caves, one of their most famous roosts being New Mexico’s Carlsbad Caverns. However, these bats will also choose to roost under bridges, in attics, and in abandoned buildings.

What Happens During Bat Hibernation

Hibernating bats will start to consume large amounts of insects in mid-October to build body fat that will nourish and protect them during hibernation.

Once a bat has found its hibernacula, or winter hibernation spot, it will enter a sleep-like state. While in this state, the bat’s normal heart rate of 200-300 beats per minute will slow to just 10 beats per minute. As well, its body temperature and breathing rate will drop. Some hibernating bats will only breathe once or twice every several minutes.

All of these slowed biological processes occur to help the bat conserve its energy and fat metabolization.

White Nose Syndrome (WNS)

white nose syndrome

White nose syndrome, or WNS, is caused by the pseudogymnoascus destructans (PD) fungus. PD has been found in multiple species of hibernating bats in Southern California and across the United States. Infection occurs via close contact between roosting bats or from contaminated surfaces within the roost.

WNS appears as a white, fuzzy coating on the muzzles, ears, and wings. It spreads quickly and penetrates deep into skin tissues. WNS causes hibernating bats to wake more often, which accelerates the rate at which stored fat metabolizes. This can cause starvation.

The penetration of WNS into wing tissue can also cause significant damage that affects many critical functions, including water balance, blood circulation, and thermoregulation.

All of these factors are what make WNS capable of killing entire bat colonies. This is bad news for all bats, especially those designated as Species of Special Concern. In Los Angeles alone, 10 species have been given this designation.

Have You Seen Bats Flying at Your Property?

Mexican Freetail Bats

If you’ve seen bats exiting from the chimney, eaves, attic, or walls of your home or another structure at dusk, they’ve likely chosen to roost there.

Bat guano contains histoplasmosis, which can cause lung disease in humans and pets. If you’ve noticed a white and fuzzy appearance on bats, this can indicate WNS infection.

In either instance, it’s important to contact a professional. With over two decades of experience in safe and humane bat removal, Animal Capture Wildlife Control uses exclusion techniques that are designed to protect bat species; visit us to learn more about our bat removal tools and techniques.