bats

bats-eat-the-birds-they-pluck-from-the-sky-while-on-the-wing

Bats eat the birds they pluck from the sky while on the wing

bats, Biology, birds, Ecology, hunting, Science / /

There are three species of bats that eat birds. We know that because we have found feathers and other avian remains in their feces. What we didn’t know was how exactly they hunt birds, which are quite a bit heavier, faster, and stronger than the insects bats usually dine on.

To find out, Elena Tena, a biologist at Doñana Biological Station in Seville, Spain, and her colleagues attached ultra-light sensors to Nyctalus Iasiopterus, the largest bats in Europe. What they found was jaw-droppingly brutal.

Inconspicuous interceptors

Nyctalus Iasiopterus, otherwise known as greater noctule bats, have a wingspan of about 45 centimeters. They have reddish-brown or chestnut fur with a slightly paler underside, and usually weigh around 40 to 60 grams. Despite that minimal weight, they are the largest of the three bat species known to eat birds, so the key challenge in getting a glimpse into the way they hunt was finding sensors light enough to not impede the bats’ flight.

Cameras, which are the usual go-to sensor, were out of the question. “Bats hunt at night, so you’d need night vision cameras, which together with batteries are too heavy for a bat to carry. Our sensors had to weigh below 10 percent of the weight of the bat—four to six grams,” Tena explained.

Tena and her team explored several alternative approaches throughout the last decade, including watching the bats from the ground or using military-grade radars. But even then, catching the hunting bats red-handed remained impossible.

In recent years, the technology and miniaturization finally caught up with Tena’s needs, and the team found the right sensors for the job and attached them to 14 greater noctule bats over the course of two years. The tags used in the study weighed around four grams, could run for several hours, and registered sound, altitude, and acceleration. This gave Tena and her colleagues a detailed picture of the bats’ behavior in the night sky. The recordings included both ambient environmental sounds and the ultra-frequency bursts bats use for echolocation. Combining altitude with accelerometer readouts enabled scientists to trace the bats’ movements through all their fast-paced turns, dives, and maneuvers.

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Bat colony checks in to hotel; 200 guests check out, unaware of rabies scare

bats, Exposure, health, infectious, rabies, risk, wyoming / /

Health officials in Wyoming are sinking their teeth into a meaty task.

Over 200 people who stayed in a hotel in Grand Teton National Park between May and July may have unknowingly been exposed to rabies, according to Wyoming Public Radio.

In an announcement on Friday, the National Park Service reported finding evidence of a bat colony in the attic. The discovery was made after there had been at least eight incidents in which guests encountered winged mammals inside the hotel.

Now, the Wyoming Health Department is trying to contact all guests who stayed in a block of rooms under the bat’s lair. Specifically, they’re reaching out to the over 200 who stayed in rooms 516, 518, 520, 522, 524, 526, 528, and 530 at the Jackson Lake Lodge between May 15 and July 27. It was on July 27 that the eighth bat run-in occurred and the hotel closed the eight rooms.

“Although there were a lot of people exposed in this incident, one positive about it is that we know who 100 percent of those people are,” Travis Riddell, director of the Teton County Public Health Department, told Wyoming Public Radio.

In Wyoming, bats are one of the two main carriers of rabies, the other being skunks. But bats are of particular concern because—unlike an extremely obvious skunk attack—people might not be aware of bat exposures.

Inconspicuous risk

The rabies virus generally transmits through saliva via bites and scratches, and bat bites and scratches are easy to miss. The most common bat in Wyoming is the small brown bat, which weighs less than half an ounce on average—though they can look larger due to their wide wings. These teeny bats, with their wee teeth, can leave bites and scratches that are not visible, do not bleed, and are not painful.

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bats-use-echolocation-to-make-mental-maps-for-navigation

Bats use echolocation to make mental maps for navigation

bats, Behavioral science, Biology, echolocation, navigation, neurobiology, Science / /

Bat maps

To evaluate the route each bat took to get back to the roost, the team used their simulations to measure the echoic entropy it experienced along the way. The field where the bats were released was a low echoic entropy area, so during those first few minutes when they were flying around they were likely just looking for some more distinct, higher entropy landmarks to figure out where they were. Once they were oriented, they started flying to the roost, but not in a straight line. They meandered a bit, and the groups with higher sensory deprivation tended to meander more.

The meandering, researchers suspect, was due to trouble the bats had with maintaining the steady path relying on echolocation alone. When they were detecting distinctive landmarks like a specific orchard, they corrected the course. Repeating the process eventually brought them to their roost.

But could this be landmark-based navigation? Or perhaps simple beaconing, where an animal locks onto something like a distant light and moves toward it?

The researchers argue in favor of cognitive acoustic maps. “I think if echolocation wasn’t such a limited sensory modality, we couldn’t reach a conclusion about the bats using cognitive acoustic maps,” Goldshtein says. The distance between landmarks the bats used to correct their flight path was significantly longer than echolocation’s sensing range. Yet they knew which direction the roost was relative to one landmark, even when the next landmark on the way was acoustically invisible. You can’t do that without having the area mapped.

“It would be really interesting to understand how other bats do that, to compare between species,” Goldshtein says. There are bats that fly over a thousand meters above the ground, so they simply can’t sense any landmarks using echolocation. Other species hunt over sea, which, as per this team’s simulations, would be just one huge low-entropy area. “We are just starting. That’s why I do not study only navigation but also housing, foraging, and other aspects of their behavior. I think we still don’t know enough about bats in general,” Goldshtein claims.

Science, 2024.  DOI: 10.1126/science.adn6269

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