Been thinking about bats. I’ve been going out on the beach after dusk to spend time with them. As a kid, I threw rocks and watched them pick up my projectiles with their echolocation. They would veer to investigate and then let the rocks fall.
Now I just watch. In the near dark, distanced from other people but not from the world of waves and insects and barely visible bats that skitter like moths above, I’m goosebumps deep in a sense of night and flight and the pandemic.
I’m at the feet of a different universe.
I’ve been spending time with bats because it’s likely the coronavirus behind COVID-19 developed among bats before it moved, possibly through a secondary host, to humans. Bats have been tied to SARS and MERS as well.
A naturalist hates to fear anything in nature. We have been trained in the art of relationships and taught that coexistence can be had even with danger. If I’m going to change my feelings about bats, I’m going to do it by understanding as much as I can about them first.
It is hard to study bats. One of my friends on the peninsula remembers a bat researcher visiting and teaching her to catch them for study by putting rocks into pantyhose and firing the pantyhose into the air. Most bats catch their prey by netting it with their wing or tail membranes then snagging it with their claws. The pantyhose caught their claws.
Ten species are found around Puget Sound. Some of them migrate, some hibernate; some form medium-sized roosts, others roost alone. They use hollow trees, cracks in bark, streambanks, caves, barns, attics. They eat all manner of flying insects. Yet our basic knowledge of their lives is wildly incomplete. One of the most commonly seen bats in Washington is the little brown bat, Myotis lucifugus, and we do not know where it migrates to spend the winter.
Worldwide there are 1,400 species of bats, representing a fifth of all mammals — flight unlocks a lot of possibilities. Flight has led to other advantages as well.
Bats have long impressed physiologists. Flight is the most physically demanding activity in any mammal. While our own most intense activities might double or triple our metabolic rate, and a running rodent’s might rise sevenfold, a flying lactating female bat’s metabolic rate can be 15 times higher than her base rate.
When a body churns through food and energy so quickly, you would expect a fast accrual of damage from the toxins that are a byproduct of metabolism. You would expect bats, as the cost of flight, to have short lifespans. Yet they can live up to 40 years, the longest lifespan proportional to their size of any mammal.
Not only that, bats routinely survive viruses like Ebola without symptoms. They have been shown to survive rabies. An old classmate of mine, Cara Brook, is at the head of new research that suggests why.
Flight is so demanding at the cellular level that bats have developed what she calls a “perpetually primed antiviral system.” The exact strategy depends on the species, but their bodies work to stitch DNA back together, create proteins that interrupt the life cycles of viruses, and constantly warn their cells to guard against toxins. In most mammals, such a system would leave tissues so constantly inflamed that death would soon follow. Bats compensate in a number of ways, including dropping some of the genes responsible for inflammation. They’ve hit a sweet spot. Their superpower may be flight, but it is only possible because of an equally super-powerful immune system.
The side effect of this is that they are very resistant to viruses. When a virus enters a population of bats, Brook’s research shows, the virus compensates for being less deadly — faced as it is with an immune system no other mammal can boast — by evolving to transmit more quickly. So when the virus transfers from bats to another mammal, it is primed to wreak fast havoc.
On the other hand, the very capability that makes them reservoirs for powerful viruses also makes bats powerful eliminators of disease. Flight requires tons of energy, and insect-eating bats eat about 50% of their body weight each night. A lactating female may eat more than her whole body weight. Each night. That’s a lot of moths and mosquitoes. Bats significantly slow insect-borne diseases in people and insect-caused damage to agriculture.
Further, researchers are beginning to do genetic research on bats to better understand how their immune systems deal with viruses. This could lead to novel treatments. It will also help us work out how and why deadly diseases emerge and the strategies that will give bats what they need to live their lives without coming into contact with humans.
That’s really the rub. You cannot cast a fearful eye on bats without casting a far more critical eye on the human history that has tended to splinter their habitats and destroy their natural food webs. Bats may carry viruses, but we are going out of our way to create conditions for their transmission.
It’s hard as a naturalist not to look at the big picture — not to feel it in your goosebumps. Bats skitter above me. I’m jealous of flight, and there’s a dangerous thrill to being out in the night. It’s like I’m at the limits of where humans should go.
All of us in the global ecosystem have superpowers that are the double edges of the proverbial sword. By spending time with bats we’ll better understand their superpowers as well as our own. We’ll learn to have a relationship with danger, to respect it — to know the boundaries beyond which we’re asking for a sword fight.
BATS OF THE KP AND BEYOND
Eight species are likely to live around the Key Peninsula: big brown bat (Eptesicus fuscus), California myotis (Myotis californicus), hoary bat (Lasiurus cinereus), little brown bat (Myotis lucifugus), long-legged myotis (Myotis volans), silver-haired bat (Lasionycteris noctivagans), western long-eared myotis (Myotis evotis), Yuma myotis (Myotis yumanensis).
Bats are nearly impossible to identify visually in flight. But new technology can analyze recordings of a bat’s echolocation calls to identify the species, even though many calls are beyond the range of human hearing.
Bats are most active in late spring, summer and fall, when insects are abundant. Most of our species migrate elsewhere for the winter. A few, such as the long-legged myotis, hibernate within 100 miles of their summering grounds. Recently, however, naturalists have discovered that others actually emerge to forage on calm winter evenings, including the silver-haired bat and California myotis. Observations of bats in winter should be noted.
Patagium: the wing membrane, stretched between arm and finger bones.
Hibernaculum: a roost where bats hibernate during the winter.
Magnetoreception: bats’ ability to use Earth’s magnetic field to tell north from south.
Flittermouse: an old English word for bat.
Bats are rare in the fossil record. One of the oldest examples is from the Green River Formation in Wyoming, dating to the Eocene about 50 million years ago. This early bat had short wings, long hind limbs and a claw on every digit, suggesting it was just as adept at scrambling around trees as flying. Its small ear suggests that early bats developed flight before they developed echolocation.