Hoary bat

The hoary bat is widely distributed across North America, probably occurring in all 50 states, and is the only land mammal native to Hawaii. Despite their wide distribution, hoary bats are seldom encountered by people. They are nocturnal, obviously, but come out later at night than most bats, after the sky is dark. They rarely use human structures as shelter, as they prefer to roost among the thick foliage of trees (often 10-15 feet above ground) or sometimes in cavities created by other animals. And hoary bats – like their cousins, the red bats – are solitary rather than colonial, making it easy to go unnoticed. They seem to prefer roosting in trees along the edges of clearings, as well as those in and along city parks. Hoary bats will forage around street lamps for the abundant insects attracted to the light.

Hoary bats are a migratory species, and many travel as far as South America for the winter. Their migration is underway by early fall. The bats will band together for the journey and may be seen before dark, among flocks of birds heading in the same direction. Some do remain north in winter, where they hibernate in insulated spaces like hollow trees, rock crevices, leaf litter, and sometimes even basements.

Hoary bats, like all NJ bats, are insect-eaters. They often forage over water and in forest clearings for moths, mosquitos, dragonflies, beetles, and other insects. They may form hunting groups at night. Interestingly, hoary bats have been seen eating vegetation and even shed snake skin. They have even been observed attacking smaller bat species.

Hoary bats use echolocation to navigate and find their prey. They emit rapid call pulses while flying. The returning echoes reveal the size, shape, distance, and trajectory of insects, enabling the bats to hone in on their prey and ultimately snatch them from the air. Hoary bats are the largest bats in NJ and their calls are the deepest; they are even audible to some people when dipping to frequencies as low as ~16 kHz.

Hoary bats mate in autumn before, during, or after migration.  Females store sperm over winter and become pregnant in the spring when they ovulate. This delayed fertilization strategy is shared by the other bats in our region. While female hoary bats generally have litters of two pups, they can have up to four and are equipped with four mammary glands to accommodate them. The pups are born between May and early June. They are nursed by their mother, clinging to her while she is in the roost and holding onto branches while she hunts each evening. The young bats begin to fly and feed on their own after about 30 days.

The average lifespan of hoary bats is very short, by bat standards. They may live just two years in the wild. Natural predators of the hoary bat include hawks and owls, and occasionally climbing animals like snakes.

As solitary “tree bats” seldom encountered by people, hoary bats have evaded the persecutions sometimes faced by bats which dwell in buildings or caves. Their preference for roosting in the open tree canopy also gives them a wider range of options than bats which depend on dead/dying trees or other specific habitats. And since hoary bats do not typically hibernate below ground, they are not susceptible to the devastating effects of White-nose Syndrome.

However, hoary bats and other migratory species are taking massive hits from wind farms along their migration routes. Recent studies estimate that around 500,000 bats (mainly red bats, hoary bats, and silver-haired bats) may now be killed annually by wind turbines in the U.S.  Researchers believe that bats are drawn to the turbines as places to perch, hunt for insects, or engage with mates, or simply for curiosity’s sake. Bats are either struck by the fast-moving blades or killed by barotrauma – the damage to air-containing organs caused by rapid pressure change. A working group called the Bats and Wind Energy Cooperative (BWEC) was formed in 2003 to tackle this emerging issue. Solutions include seasonal adjustments to turbine cut-in speeds (wind speed at which the blades start spinning), acoustic and/or light deterrents, and avoiding turbine development in high-risk locations.

In 2013, the New Jersey Endangered and Nongame Advisory Committee recommended a Special Concern status for this species, but no formal rule proposal has been filed to date.

Learn about the work being done to research and protect NJ’s bats at our Bat Project webpage.