Bats cooperate for finding food


This 2014 video says about itself:

Secrets and Mysteries of Bats – Nature Documentary

This 48-minute documentary explores the world of bats and the scientists who study them — including the late Donald Griffin, a Harvard zoologist who was the first to describe their echolocation ability in the 1940s. Using 3-D graphics to recreate the bats’ acoustic vision and shooting with infra-red and high-speed cameras, this film offers an exhilarating “bat’s-eye” journey into the night.

From the University of Maryland in the USA:

Unpredictable food sources drive some bats to cooperatively search for food

December 13, 2018

Summary: With the help of novel miniature sensors, biologists have found that bat species foraged socially if their food sources were in unpredictable locations, such as insect swarms or fish schools. In contrast, bats with food sources at fixed locations foraged on their own and did not communicate with one another while foraging or eating.

Humans aren’t the only species that have dinner parties. Scientists have observed many animals, including bats, eating in groups. However, little was known about whether bats actively help each other find food, a process known as social foraging.

With the help of novel miniature sensors, an international group of biologists that included University of Maryland Biology Professor Gerald Wilkinson found that bat species foraged socially if their food sources were in unpredictable locations, such as insect swarms or fish schools. In contrast, bats with food sources at fixed locations foraged on their own and did not communicate with one another while foraging or eating. The results of the study were published in the November 19, 2018 issue of the journal Current Biology.

“We were able to show that bats who can’t predict where their food will be are the ones that cooperate with each other to forage”, Wilkinson said. “And I don’t think they are unique — I think that if more studies are done, we will find that other bat species do similar things.”

The researchers selected five bat species from around the world for the study — two species with unpredictable food sources and three with predictable food sources. They fit each bat with a small, lightweight sensor that operated for up to three nights. Because the sensor only weighed approximately 4 grams, it did not hinder the bat’s movements. The sensor recorded GPS data to log each bat’s flight path and audio in ultrasonic frequencies to document bat calls. The researchers recaptured each bat to download the data. In all, the researchers tracked 94 bats in this study.

Edward Hurme, a UMD biological sciences graduate student in Wilkinson’s laboratory and a co-lead author of the paper, tracked one of the bat species — the Mexican fish-eating bat, which lives on a remote Mexican island.

“We took a fishing boat to an uninhabited island where these bats live and camped there for a month at a time”, Hurme said. “Field work can be challenging. One time, a hurricane came and all we could do was hide in the tent. Fortunately, we survived and so did our data.”

After collecting data on all five bat species, the researchers charted the bats’ flight paths and analyzed the audio recordings. They listened for the distinctive, species-specific calls the bats make during normal flight and when trying to capture prey. The research team used this information to map where and when the bats found and ate food and whether other bats were nearby.

The results showed that the three species of bats that eat predictable food sources, such as fruits, foraged on their own. When they found food, they also ate alone. This makes sense, according to Wilkinson, because they didn’t need any help finding food. In fact, having other bats around could create harmful competition for food.

In contrast, the two species of bats with unpredictable food sources often flew together with other members of their species. Moreover, when a tracked bat found prey, other individuals nearby also began to forage. The findings suggest that these bats forage cooperatively and socially within their own species.

The researchers also found that socially foraging bats may eavesdrop on one another by staying close enough to hear each other’s feeding calls.

“We tested this hypothesis by playing recordings of white noise, normal calls and feeding calls for these bats to hear”, Hurme said. “We found that bats who heard normal calls became more attracted to the speakers than those who heard white noise. And when we played feeding calls, bats dive-dombed the speakers.”

The next step for this research is to investigate what strategies bats use in social foraging. In particular, Hurme hopes to discover whether these bats pay attention to the identity of their fellow foragers.

“We would like to know if socially foraging bats will follow any member of their own species or if they prefer specific individuals who are the most successful at finding food”, Hurme said. “There is some evidence that bats can recognize each other by voice, so we are working on ways to identify individuals by their calls.”

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Bats at Panama bird feeders


This video says about itself:

Bats Visit Panama Feeders in Middle of the Night – Nov. 13, 2018

Birds aren’t the only winged creatures you’ll find enjoying the offerings at the Panama fruit feeders. Watch here as a group of bats take turns foraging on sweet nectar in the middle of the night!

Watch LIVE 24/7 with highlights and viewing resources at http://allaboutbirds.org/panamafeeders

The Panama Fruit Feeder Cam is a collaboration between the Cornell Lab of Ornithology and the Canopy Family.

How bats fly, unique new study


This 8 November 2018 video says about itself:

Unique study shows how bats manoeuvre

For the first time, researchers have succeeded in directly measuring the aerodynamics of flying animals as they manoeuvre in the air. Previously, the upstroke of the wings was considered relatively insignificant compared to the powerful downstroke but, in a new study, biologists at Lund University in Sweden have observed that it is on the upstroke of the wings that bats often turn.

From Lund University:

November 8, 2018

“Until now, we have not known very much about what animals actually do when they fly, since we have focused on steady flight. Steady flight is in fact not very common for animals flying out in the wild. We have now conducted direct aerodynamic measurements on bats and we can see how flexible they are. They turn in several different ways depending on where they are in the wing-beat”, explains Per Henningsson, a biologist at Lund University.

“It is really fascinating to see how complex and elegant the pattern of movement is, and how the bats choose the best solution just as they decide to start a manoeuvre,” he continues.

For the bats, flight technique with fast manoeuvres at high speed is important to successfully capture insects in flight, as well as to avoid collision with various obstacles such as trees and buildings.

The results could be significant in the development of the next generation of drones.

“One of the main challenges for the industry is about control and stability and enabling drones to avoid obstacles easily. In that context, our results are very relevant”, says Per Henningsson, who does not exclude the possibility of future drones being equipped with flapping wings.

The study was conducted on two [brown] long-eared bats that were trained to fly in a wind tunnel. As prey, the researchers used mealworms attached to a device that could be moved laterally. By moving the device to the right or to the left, the researchers made the bats turn to follow the direction of the prey. The researchers visualised the air flow and filmed the animals with high-speed cameras. This allowed them to link the aerodynamics to the movements.

The researchers behind the study are biologists from Lund University and the University of Southern Denmark.

How moths evade bats


This 5 July 2018 video says about itself:

Watch how battles with bats give moths such flashy tails

Long tails fool bats into striking in the wrong place.

Read more here and here.

From the Acoustical Society of America in the USA:

Moths survive bat predation through acoustic camouflage fur

November 6, 2018

Moths are a mainstay food source for bats, which use echolocation (biological sonar) to hunt their prey. Scientists such as Thomas Neil, from the University of Bristol in the U.K., are studying how moths have evolved passive defenses over millions of years to resist their primary predators.

While some moths have evolved ears that detect the ultrasonic calls of bats, many types of moths remain deaf. In those moths, Neil has found that the insects developed types of “stealth coating” that serve as acoustic camouflage to evade hungry bats.

Neil will describe his work during the Acoustical Society of America’s 176th Meeting, held in conjunction with the Canadian Acoustical Association’s 2018 Acoustics Week, Nov. 5-9 at the Victoria Conference Centre in Victoria, Canada.

In his presentation, Neil will focus on how fur on a moth’s thorax and wing joints provide acoustic stealth by reducing the echoes of these body parts from bat calls.

“Thoracic fur provides substantial acoustic stealth at all ecologically relevant ultrasonic frequencies,” said Neil, a researcher at Bristol University. “The thorax fur of moths acts as a lightweight porous sound absorber, facilitating acoustic camouflage and offering a significant survival advantage against bats.” Removing the fur from the moth’s thorax increased its detection risk by as much as 38 percent.

Neil used acoustic tomography to quantify echo strength in the spatial and frequency domains of two deaf moth species that are subject to bat predation and two butterfly species that are not.

In comparing the effects of removing thorax fur from insects that serve as food for bats to those that don’t, Neil’s research team found that thoracic fur determines acoustic camouflage of moths but not butterflies.

“We found that the fur on moths was both thicker and denser than that of the butterflies, and these parameters seem to be linked with the absorptive performance of their respective furs”, Neil said. “The thorax fur of the moths was able to absorb up to 85 percent of the impinging sound energy. The maximum absorption we found in butterflies was just 20 percent.”

Neil’s research could contribute to the development of biomimetic materials for ultrathin sound absorbers and other noise-control devices.

“Moth fur is thin and lightweight,” said Neil, “and acts as a broadband and multidirectional ultrasound absorber that is on par with the performance of current porous sound-absorbing foams.”