Home & Garden Columns

Cal Day at the Museum of Vertebrate Zoology (MVZ) is a reliable venue for stories. Last year it was a conversation with a maybe eight-year-old naturalist about gopher snakes at the Berkeley Marina. This year I wound up talking to a young woman who was presiding over a tabletop display of dead bats. One in particularly caught my eye, a larger-than-average bat with a striking two-tone wing pattern: a hoary bat (Lasiurus cinereus). 

(That snickering in the back row will stop immediately. “Hoary” is a respectable Old English word connoting frost. In addition to the hoary bat, the hoary redpoll and the hoary marmot are members in good standing of North America’s fauna. So just cut that right out). 

What the Cal student told me was that hoary bats, unlike many of their kin, roost in trees and shrubs, and that UC’s grounds maintenance crew used to bring them to the MVZ a lot (whether dead or alive was not clear). I was intrigued enough to ask a friend who had recently retired as the university’s lead groundskeeper about bats in trees. He remembered dealing with Mexican free-tailed bats in the crevices of buildings, including the women’s faculty club, but not the larger hoarys. 

Still wondering what kind of shape those bats were in, I followed up with Patricia Winters, Education and Rehabilitation Director of the California Bat Conservation Fund, whose “BATMAM” license plate you may have noticed. I thought I recalled her talking about scrub-jay predation on tree-dwelling bats a few years ago, and she confirmed that it was frequent. Crows do it too.  

“They often come into our rehab centers with various injuries,” Winters said via email. “I presently have three hoary bats in captivity who were too badly injured to ever regain the ability to fly. They are fierce fighters when they first come in, but quickly learn to realize that we are not going to hurt them, and calm down. I have had one hoary female for eight years now. She was a marvelous school bat, going to hundreds of presentations with me, but she is now retired due to her old age. The other two hoarys, both female, are now getting ready to take her place.” 

Winters was kind enough to provide the accompanying photograph of the late Punkinhead, a male hoary bat who was in the rehab program for several years. How can you not love that face? As cuddly as they may appear, it’s not a good idea to pet them, should the opportunity arise. “Do not reach out and attempt to touch them,” Winters warns. “They will never attack people, but they will defend themselves and can give a nasty bite if they are handled.” Hoary bats will typically warn against such familiarities with what one book calls “a most startling rattling hiss accompanied by an impressive show of teeth.” 

Active late in the evening, hoarys have a strong direct flight. Their food habits are not well documented; in addition to the expected insects, one was observed attacking a western pipistrelle, a smaller species of bat. Unlike the high-pitched echolocation calls of most other bats, their in-flight chatter is audible to the human ear. 

These mostly solitary bats have a huge range, from the Canadian tree line into South America. Males and females seem to follow different northbound routes through California in spring, females in the lowlands and coastal valleys, males in the foothills and mountains. The sexes have been found together during fall migration, and may travel in small flocks. Up to 21 have been counted at the same time on South Farallon Island. 

But they haven’t stopped there. Humans aside, the hoary bat is the only land mammal to reach the Hawai’ian islands on its own. Island bats, known as ope’ape’a, have been classified as a separate subspecies and their fur is a bit redder, but otherwise they’re pretty much standard hoary bats. 

Which makes you think about the vagaries of evolution. Millions of years ago, the seed of a California tarweed reached Hawai’i probably clinging to the feathers of a migratory bird; its progeny include the bizarre yuccalike silversword plants of Haleakala Crater. An ancestor got out there some 3.5 million years ago and gave rise to a whole slew of red, yellow, and black songbirds with a dazzling array of bill shapes and functions: seed-crushers, tweezers, picks and probes. Some, like the beak of the extinct Lana’i hookbill, still have scientists scratching their heads. 

As recent work with the Darwin’s finches of the Galapagos Islands suggests, it could be that it’s somehow easier to rewire the developmental pathways that make a beak than for other body parts. Or the Hawai’ian bats may simply not have been there long enough for their own evolutionary radiation; the oldest known fossils are less than 100,000 years old. Time and chance, like the man said. 

Photograph by Patricia Winters, California Bat Conservation Fund: Punkinhead, a rehabilitated hoary bat.