International Bat Appreciation Day

In case you missed it, International Bat Appreciation Day was April 17. It’s easy to overlook, crammed up against Earth Day on April 22 (today, in fact). The bat appreciation celebration was founded by Bat Conservation International (BCI) in 1982 to recognize the importance of protecting them. And they truly do deserve our appreciation. Far from the bad reputation they get from being associated with vampires, bats help control crop-damaging insect pests and create fertilizer. They pollinate fruit and flowers. They’re the only mammals ever to have evolved sustained flight. They echolocate. They’re cute.

By the numbers. With about 1,400 species, or 20% of all described mammals, bats form the second-largest group after rodents. They live everywhere on the planet except for the poles. Bats come in two types. They are the Megabats (“Yinpterochiroptera”) – big bats that look like flying chihuahuas and eat fruit and pollen. They are (usually) larger than their cousins the Microbats (“Yangochiroptera”), which are primarily insectivorous. Their difference in diet has led to the development of echolocation in the Microbats, which they use to track their prey as it flies. How they do that is pretty cool, sending out a signal and tracking the pulses generated back by even a tiny moth in midair swerving to evade its pursuer.

The Egyptian fruit bat or Egyptian rousette (Rousettus aegyptiacus), one of the few Megabat species that can echolocate. Photo: Eggybird 2006.

But because nothing in nature is tidy, it turns out that there’s a group of bats, the rousette bats, that have re-evolved the ability to echolocate, after they lost it, following the split away from their common ancestor with the Microbats. But instead of generating ultrasound with their larynx like the Microbats, the rousette bats use their tongues to make the clicks, called “vocal echolocation”. This example of re-evolution is fascinating because it’s very rare (imagine if dolphins re-evolved the ability to walk on land). Presumably it helps them navigate the caves they inhabit.

Benefits to ecosystems. Bats play varied roles in the ecosystems in which they live. For one thing, Microbats are voracious hunters. While some consume fish, frogs, scorpions, and even blood, their principle diet is an enormous variety of insects. Different species specialize on different kinds of insects, but the group as a whole chows down on whatever flying insect is there, including moths, flies, leaf hoppers, beetles, and grasshoppers. They consume 25% – 70% of their body mass of insects each night and with lactating females it’s 100%. And while they’re foraging, they also become prey to other animals like owls, hawks, falcons, snakes, raccoons, opossums, and even crocodiles. Larger bats will also prey on smaller ones.

Flying foxes in their nightly fly-over of Sydney Habour on their way to foraging grounds. Photo: Naddsy 2006.

The Megabats focus on fruit and flowers and, as a result, can play important roles in pollination and seed dispersal. Bat pollination occurs in more than 528 species of 67 families and 28 orders of flowering plants worldwide. These bats aren’t usually dependent on pollen as their only food source. Most pollenivorous bats are primarily fruit eaters. And as they travel they disperse the seeds of the fruit they eat. Considering that 50–90% of trees and shrubs in the tropics produce fleshy fruits for adapted for consumption and seeds that pass through the guts of vertebrates unharmed, frugivorous bats play an enormous role in maintenance and regeneration of the rainforest biome. And the same guano that disperses the seeds also fertilizes the soil. A colony of one million Brazilian free-tailed bats can contribute to 22kg of nitrogen-rich guano nightly. Bat guano supports a diverse community of organisms including bacteria, fungi, lichens, and invertebrates of many types.

Mexican free-tailed bats exiting Bracken Bat Cave. Photo: USFWS/Ann Froschauer

Benefits to us. Bats provide major and often neglected economic benefits to us. Foraging Microbats only eat the nutritious abdomen of the insect, greatly increasing the number consumed by each bat. Based on fecal sample analyses, a single colony of 300 evening bats Nycticeius humeralis in Indiana consumes an estimated 6.3 million insects annually. Loss of bats in the United States would lead to agricultural losses estimated at from $3.7BN to $53BN per year, mostly from the Midwest. But it’s not just crop pests. A colony of 30,000 bats called the southeastern myotis Myotis austroriparius in Florida eats more than 15 tons of mosquitoes within its annual diet of 50 tons of insects. Think of that next time you’re by the pool.

Although insects pollinate most plants, many of those for which bats perform this service are economically important. Durian, a large spiky fruit that smells infamously like a locker room, opens its flower at dusk to be pollinated almost exclusively by flying foxes Pteropus vampyrus, another Megabat. This fruit is ubiquitous in Southeast Asian cuisine and the crop is worth more than $230 million annually. Bananas and agave are also principally pollinated by bats. In 2005 it was estimated that the value of world food crop production aided by fruit bats was $200 billion, or 9.5% of global production. The value of their role in seed dispersal helping to revegetate rainforests denuded by logging is incalculable, when you consider the effect of declining forest cover on climate change.

Scanning electron micrograph of a bat hair colonized by Pseudogymnoascus destructans, the fungus that causes white nose syndrome. Photo: Gudrun Wibbelt et al. 2011.

Bats are in trouble. Despite the obvious benefits of bats, they’re often persecuted and many are under considerable threat. Bat Conservation International recently released the 2023 State of the Bats report that stated that 52% of Bat Species Across the Continent are at risk of severe population decline. Threats to bats include climate change, habitat loss, wind energy, and disease. When these issues are compounded, they make the bats especially vulnerable.

In particular, the fungal disease “white-nose syndrome” is devastating to hibernating bats in the United States and Canada. Three species are especially susceptible – little brown bats Myotis lucifugus, northern long-eared bats Myotis septentrionalis, and tricolored bats Perimyotis subflavus. Ninety percent of the populations of these species – hundreds of millions of bats – have been wiped out. Destruction and disturbance of bat roosts is a major threat, especially for bats in caves. Interestingly, climate change which is spelling disaster for so many species, may help bats with survival of white nose syndrome. The fungus that causes the disease, Pseudogymnoascus destructans, is a cold-loving species. As the climate warms, researchers suggest that bats may become less effected. (This is in contrast to amphibians, where rising temperatures has been found to be linked to the occurrence of chytrid-related disease, caused by another devastating fungus sending many frog and salamander species to the brink of extinction.)

Little brown bats in a bat box. Photo: Darrin Samborski, US Forest Service

How to help bats? Fortunately there are things we can do help them. A few months ago, I wrote a post about creating wildlife habitat in your garden. BCI has released a basic guide which will get you started attracting bats to your backyard and supporting them once you do. It all amounts to keeping your garden as natural as possible, dark at night, with the house cats firmly tucked up inside. If you’re especially ambitious, you can make a bat house and a guide to doing that is here.

I’m glad there’s a day devoted to celebrating bats. Bats’ order, Chrioptera, is only one of thousands of orders in the animal kingdom, so there can’t be a day for everything. But they touch so many other parts of our ecosystem’s function and create such benefits to our daily lives, that they truly deserve it. Happy International Bat Appreciation Day. And happy Earth Day.

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