Bats as Climate Change Canaries

Illustration by Edward Steed

The impact of changing weather patterns becomes particularly evident when looking at the interrelationships of animal life cycles based on season. When it comes to habitat, conservationists are winning some battles, but climate change will require longer range goals.

The Changing Climate Inside the World’s Largest Bat Colony

The migration patterns of the Bracken Cave bats are changing, adapting to the rapid rate of warming, but experts say these adaptations won’t be enough to counter the effects of climate change.

On July 23rd, another group of scientists published an article, in the journal Nature Communications, titled, “Adaptive Responses of Animals to Climate Change are Most Likely Insufficient.” There now exists plenty of evidence that animal behavior is changing, adapting to the rapid rate of warming. These adaptations include, most clearly and systematically, as in the case of the Bracken Cave bats, an alteration in the timing of seasonal behaviors like reproduction, hibernation, and migration. But over all, the authors found, these changes won’t be enough to counter the effects of climate change; in some cases, animals’ adaptations might harm them more than help them. The Columbian ground squirrel, for example, has begun emerging from hibernation later, and has been weaker as a result. What this means, of course, is that animals, which are already going extinct at a rate tens to hundreds of times higher than they have in the past ten million years, primarily because of the rapid increase in human population and development, are going to have an even harder time surviving as climate change advances. As a sweeping United Nations report on biodiversity, published in May, concluded, accelerating climate change is a “direct driver” of species extinction and biodiversity destruction, and is “increasingly exacerbating the impact of other drivers.”

Stepanian and Wainwright are now using their radar analysis to track the spectacular emergence of mayflies in the Upper Midwest every summer. Although they haven’t published their findings yet, their data suggests that the number of mayflies has decreased significantly over the past few years. Stepanian is also now using radar to study the migration patterns of Australian bats, specifically gray-headed flying foxes—one of the largest types of bat in the world, with wingspans that can reach three feet. Last November, a heatwave in northern Australia killed one-third, or twenty-three thousand, of the nation’s spectacled flying foxes (also known as spectacled fruit bats) in just two days. Unable to survive the temperatures, which exceeded a hundred and seven degrees Fahrenheit, they fell dead from the sky.

At Bracken Cave, the Mexican free-tailed bats’ shifting migration habits “very likely is due to prey availability, Stepanian told me. The bats survive on insects, which they eat all night as they fly across southern Texas. Insects are very sensitive to temperature, and if it is cold they cannot fly. So hotter winters in Texas mean, in theory, more insects, which means that the bats don’t have to make the long trip south and back to find food in the winter. “A positive spin on this is that the bats are adapting as their environment changes,” Stepanian told me. “The question is, How long can they sustain that adaptation?

Read the entire article here.

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