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Jennifer Krauel

Exploring aeroecology and life in the night sky

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  • About me
    • CV
    • Publications
    • Reflections
  • Aeroecology
  • Research
  • Blog
  • Media
  • Contact
  • Search
Photo: free-tailed bats clustered in a crevice under a bridge

Free-tailed Bats

Photo: free-tailed bat held in a handMuch of my research has involved the Brazilian free-tailed bat, Tadarida brasiliensis, which is found across the southern US and all the way down into southern South America. These are the bats you can see streaming out at dusk from caves and under bridges in the US southwest to eat moths. The colony at Bracken Cave in Texas may be the largest aggregation of mammals in the world with many millions of individuals each summer, and it’s even visible on weather radar. These bats are also famous for their consumption of agricultural pests, preventing damage to crops and saving farmers millions of dollars in reduced pesticide use. They even contribute to the suppression of insect pesticide resistance by consuming insects emerging over fields of GMO crops.

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The ultimate aeroecology predator

I’m particularly interested in these bats because they fly very fast and very high, making them an ideal candidate for studying high-altitude predator-prey interaction. But there are so many other fascinating things about them! For example, males stake out territory and sing complex songs to attract females. In summer female bats gather in colonial maternity roosts, and when they return from foraging to nurse their pups they find them among masses of 400-500 pups per square foot by recognizing their calls and scent. They’ll happily use bat houses if caves aren’t available. Probably because they live in huge colonies, they are not very aggressive compared to other bat species. Freetails are sweeties!

Brazilian or Mexican? You might see these bats referred to as Mexican free-tailed bats elsewhere. They’re the same species! I prefer to use the name Brazilian because that makes it more clear that it’s all one species throughout the new world.

Long-distance migration

We know quite a bit about these bats because they are colonial. Before we learned that it was harmful to the bats, many hundreds of thousands were captured in caves and banded and some of those bands were recovered in remote places. That’s how we know that some of them travel thousands of kilometers during migration.

Their migratory behavior is complex. Some individuals migrate long distances, such as the females that move between central Mexico and as far north as Oklahoma. Scientists used to think that freetails migrated along corridors, and they might, but genetic tests don’t support this idea. An increasing number of bats are choosing to over-winter in Texas rather than returning to Mexico, but we don’t know why. Others, such as those in the eastern US are thought not to migrate. Their range in the eastern US is expanding, however, and they are now routinely found in Virginia and Tennessee. Migration in the US west and elsewhere in their range is very poorly understood. Even though these bats are relatively well-studied compared to most species, we still know very little about how and why they migrate.

Conservation

Photo: close-up of a free-tailed bat faceFor the moment, at least, these bats do not appear to be declining. However, as insectivores and consumers of migratory insects, they will be affected by global declines in insect diversity and abundance as well as predicted shifts in wind and temperature due to climate change. The fungus responsible for WNS has been found in Texas but the impact on free-tailed bat colonies is unknown. Finally, these bats are often killed at wind turbines and the proliferation of wind energy especially around maternity caves is an ongoing threat.


Questions? Comments? There’s more information in the blog entries below, but please feel free to start a conversation with me on Twitter: Tweet to @batgrrl

Screenshot: Rapid range expansion of the Brazilian free-tailed bat

Free-tailed bats coming your way?

October 17, 2018

Free-tailed bats coming your way?Read More

Screen shot: Free-tailed bats adjust foraging behavior in response to migratory moths

Bats adjust foraging behavior in response to migratory moths

May 1, 2018

Bats adjust foraging behavior in response to migratory mothsRead More

Screen shot of a radar showing echos of bats and insects

The Batscan!

April 12, 2018

The Batscan!Read More

Screen shot: Predator-prey interaction reveals local effects of high-altitude insect migration

Bats eat migratory moths! Lots of them!

February 11, 2018

Bats eat migratory moths! Lots of them!Read More

Screenshot: Patterns of Bat Distribution and Foraging Activity in San Francisco

Bats in the city

October 16, 2017

Bats in the cityRead More

Screen shot: Weather-driven dynamics in a dual-migrant system: moths and bats

The answer is: cold fronts.

September 13, 2015

The answer is: cold fronts.Read More

Map of fronts, high and low pressure, and wind over the US

A river of life flowing overhead in the dark

October 6, 2013

A river of life flowing overhead in the darkRead More

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Your AeroEcoTour Guide:

mmHi, I'm Dr. Jennifer Krauel. I’m an ecologist who's fascinated by animal migration, especially when it comes to bats and insects and at high altitudes. My research is driven by a deep desire to conserve and protect biodiversity. Read more »

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Aeroecology

What is aeroecology? »
  • bat migration
  • conservation
  • free-tailed bats
  • insect migration
  • nocturnal aeroecology
  • predator-prey interaction
  • radar aeroecology
  • tools
  • why does it matter?
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