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Brown Long-eared Bat - Plecotus auritus
Brown Long-eared Bat - Plecotus auritus

[Image: Brown-long-eared-bat-leaving-roost-in-hollow-tree.jpg]

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Chiroptera
Suborder: Microchiroptera
Family: Vespertilionidae
Genus: Plecotus
Species: Plecotus auritus

The brown long-eared bat or common long-eared bat (Plecotus auritus) is a fairly large European bat. It has distinctive ears, long and with a distinctive fold. It is extremely similar to the much rarer grey long-eared bat which was only validated as a distinct species in the 1960s.

An adult brown long-eared bat has a body length of 4.5-4.8 cm, a tail of 4.1-4.6 cm, and a wing length of 4-4.2 cm. The ears are 3.3-3.9 cm in length, and readily distinguish this from most other bat species.

They are relatively slow flyers compared to other bat species.

[Image: Brown-long-eared-bat.jpg]

It is found throughout Europe, with the exception of Greece, southern Italy and southern Spain. The UK distribution can be found on the National Biodiversity Network website and can be seen here.

This species appears to prefer caves as roosting sites, but roosts in trees holes, buildings and bat boxes, as well. The roosts in trees may be close to the ground.

It hunts above woodland, often by day, and mostly for moths, gleaning insects from leaves and bark. This is one of the bats for which eyesight is more important than echolocation in finding prey.

[Image: Brown-long-eared-bat-in-flight-chasing-moth.jpg]

Echolocation is used to find prey. The frequencies used by this bat species for echolocation lie between 27–56 kHz, have most energy at 45 kHz and have an average duration of 2.5 ms.

Bats' flight technique could lead to better drones

Date: May 4, 2016
Source: Lund University

[Image: 160504121446_1_900x600.jpg]
This is a photo of a flying bat.
Credit: Anders Hedenstrom / Lund University

Long-eared bats are assisted in flight by their ears and body, according to a study by researchers at Lund University in Sweden. The recent findings improve researchers' understanding of the bats' flying technique and could be significant for the future development of drones, among other things.

Contrary to what researchers previously assumed, Christoffer Johansson Westheim and his colleagues at Lund University show that long-eared bats are helped in flight by their large ears.

"We show how the air behind the body of a long-eared bat accelerates downwards, which means that the body and ears provide lift. This distinguishes the long-eared bats from other species that have been studied and indicates that the large ears do not merely create strong resistance, but also assist the animal in staying aloft," says Christoffer Johansson Westheim.

The findings entail a greater understanding of the flight technique of bats. They also highlight the evolutionary conflict between flying as efficiently as possible and eco-locating, i.e. discovering objects by sending out soundwaves and perceiving the resulting echoes.

Another discovery made during the experiments and never previously described in research is how the bats generate forward motion when flying slowly. The forward motion is generated when the wings are held high and away from the body at the end of each beat.

"This specific way of generating power could lead to new aerodynamic control mechanisms for drones in the future, inspired by flying animals," says Christoffer Johansson Westheim.

The experiments were conducted in a wind tunnel in which trained bats flew through thin smoke to reach a stick with food on it. Meanwhile the researchers aimed a laser beam at the smoke behind the bats and took pictures of the illuminated smoke particles. The researchers measured how the smoke moved to calculate the forces generated by each beat of the bats' wings.


Story Source: Lund University. "Bats' flight technique could lead to better drones." ScienceDaily. (accessed May 5, 2016).

Journal Reference:
L. Christoffer Johansson, Jonas Håkansson, Lasse Jakobsen, Anders Hedenström. Ear-body lift and a novel thrust generating mechanism revealed by the complex wake of brown long-eared bats (Plecotus auritus). Scientific Reports, 2016; 6: 24886 DOI: 10.1038/srep24886

Large ears enhance perception of echolocation and prey generated sounds in bats. However, external ears likely impair aerodynamic performance of bats compared to birds. But large ears may generate lift on their own, mitigating the negative effects. We studied flying brown long-eared bats, using high resolution, time resolved particle image velocimetry, to determine the aerodynamics of flying with large ears. We show that the ears and body generate lift at medium to cruising speeds (3–5 m/s), but at the cost of an interaction with the wing root vortices, likely reducing inner wing performance. We also propose that the bats use a novel wing pitch mechanism at the end of the upstroke generating thrust at low speeds, which should provide effective pitch and yaw control. In addition, the wing tip vortices show a distinct spiraling pattern. The tip vortex of the previous wingbeat remains into the next wingbeat and rotates together with a newly formed tip vortex. Several smaller vortices, related to changes in circulation around the wing also spiral the tip vortex. Our results thus show a new level of complexity in bat wakes and suggest large eared bats are less aerodynamically limited than previous wake studies have suggested.

Attached to this post:[Image: attach.png] Ear_body_lift_and_a_novel_thrust_generating_mechanism_revealed_by_the_complex_wake_of_brown_long_eared_bats__Plecotus_auritus_.pdf (1.84 MB)
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Winging it: How do bats out-maneuver their prey?

Date: July 5, 2017
Source: Society for Experimental Biology

[Image: 170705132911_1_900x600.jpg]
Brown long-eared bat swooping in for a tasty treat.
Credit: Prof Anders Hedenström

Bats catch food 'on the wing' without touching the ground, but how do they do it? A new study by Per Henningsson at Lund University, Sweden is the first of its kind to analyse the aerodynamics of bats performing manoeuvers during flight.

"This physically demanding feat requires the bat to pick up prey with high precision, while also coping with winds and air turbulence created by the foliage and branches surrounding them," explains Dr Henningsson. In order to handle these difficult flying conditions, bats must have incredible control over their wings to manoeuver around obstacles and through tight spaces to catch their prey.

By flying Brown long-eared bats in a wind tunnel and allowing them to chase after a tempting prey, Dr Henningsson and the team use a flow visualisation technique called particle image velocimetry (PIV) to analyse how the bat's wings move through the air.

"We let the bats perform a simple lateral manoeuvre in our wind tunnel so that we can study how the animals initiate, move through and terminate the manoeuvres before stabilizing again," says Dr Henningsson.

While these techniques have been used on bats and other flying animals before, this is the first time that the manoeuvring aspects of bat flight have been examined. Understanding how these bats have evolved to master their wing control to such a fine degree. "In particular the insect eating bats have to be very skilled at manoeuvring flight since they need to be able to capture their (sometimes evasive) prey in the air," says Dr Henningsson.

It's not just bats in the spotlight however, Dr Henningsson and his team are also conducting the same experiments with birds and insects in order to compare their ability to manoeuvre: "The wings of the three groups are rather different, so one might expect the aerodynamics to be very different, but we may find some interesting similarities."

Based on their short, broad and membranous wings, Dr Henningsson believes that the Brown long-eared bats are likely to have a high level of aerodynamic control for manoeuvring compared to the other animal groups, but concludes that "surprises should probably be expected!"

Story Source: Society for Experimental Biology. "Winging it: How do bats out-maneuver their prey?." ScienceDaily. (accessed July 6, 2017).
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The pros and cons of large ears

Date: November 10, 2017
Source: Lund University

[Image: 171110084634_1_900x600.jpg]
Credit: Anders Hedenström

Researchers at Lund University in Sweden have compared how much energy bats use when flying, depending on whether they have large or small ears.

Large ears increase air resistance, meaning that long-eared bats are forced to expend more energy than species with small ears. On the plus side, large ears generate more lift and provide better hearing.

Good hearing is a prerequisite for bats' ability to echolocate, i.e. sense the echo of the sound waves they emit in order to locate and home in on their prey.

The research results therefore show that large ears have both pros and cons. Christoffer Johansson Westheim, senior lecturer at Lund University, believes that evolution has made a compromise.

"The crux is being able to fly as efficiently as possible while also having optimal echolocation ability. Bats can't be the best at both these things at the same time," he says.

The research findings also support the hypothesis that birds migrate to a greater extent than bats, and over longer distances, because bats' ears create resistance that makes flying more energy-intensive.

"The bats' external ears act as a pair of brakes -- something that birds don't have," he says.

Previous research about the effect of ears on bat flight has been based on models. This is therefore the first time that researchers have quantified the effect of the ears when studying bats flying freely in a wind tunnel. The study was conducted by biologists in Lund together with a colleague from Denmark.

The researchers have studied and compared two species of bat, one with large ears and one with small ears. The study involved using high-speed cameras to photograph laser-illuminated smoke particles in the air as the bats fly. By studying the air movements, the researchers then calculated the forces and the energy needed for flying.

Christoffer Johansson Westheim is not surprised by the results, although they have raised questions about what evolution is optimising.

"When we are studying flying animals, we know that it's the most energy-costly form of movement per time unit, and therefore we think it would be important for evolution to minimise energy consumption for the sake of flying. However, what we see here is that other characteristics, such as efficient echolocation, can be just as important in certain circumstances. Consequently, evolution makes a compromise."

Could the bat research help to improve the flying capability of drones?

"If you are going to have things sticking out of the fuselage, you can try to design them so that they generate aerodynamic lift -- in much the same way as large bat ears," he says.

Watch bat flying: 

Story Source: Lund University. "The pros and cons of large ears." ScienceDaily. (accessed November 10, 2017).

Journal Reference:
Jonas Håkansson, Lasse Jakobsen, Anders Hedenström, L. Christoffer Johansson. Body lift, drag and power are relatively higher in large-eared than in small-eared bat species. Journal of The Royal Society Interface, 2017; 14 (135): 20170455 DOI: 10.1098/rsif.2017.0455

Bats navigate the dark using echolocation. Echolocation is enhanced by external ears, but external ears increase the projected frontal area and reduce the streamlining of the animal. External ears are thus expected to compromise flight efficiency, but research suggests that very large ears may mitigate the cost by producing aerodynamic lift. Here we compare quantitative aerodynamic measures of flight efficiency of two bat species, one large-eared (Plecotus auritus) and one small-eared (Glossophaga soricina), flying freely in a wind tunnel. We find that the body drag of both species is higher than previously assumed and that the large-eared species has a higher body drag coefficient, but also produces relatively more ear/body lift than the small-eared species, in line with prior studies on model bats. The measured aerodynamic power of P. auritus was higher than predicted from the aerodynamic model, while the small-eared species aligned with predictions. The relatively higher power of the large-eared species results in lower optimal flight speeds and our findings support the notion of a trade-off between the acoustic benefits of large external ears and aerodynamic performance. The result of this trade-off would be the eco-morphological correlation in bat flight, with large-eared bats generally adopting slow-flight feeding strategies. 
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  • Claudiu Constantin Nicolaescu
Unique study shows how bats maneuver

Date:  November 8, 2018
Source:  Lund University

[Image: 181108134132_1_900x600.jpg]
Long-eared bat flying (stock image).
Credit: © Geza Farkas / Fotolia

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.
"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 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.
Watch bat in flight: 

Story Source: Lund University. "Unique study shows how bats maneuver." ScienceDaily. (accessed November 8, 2018).

Journal Reference:
  1. Per Henningsson, Lasse Jakobsen, Anders Hedenström. Aerodynamics of manoeuvring flight in brown long-eared bats (Plecotus auritus). Journal of The Royal Society Interface, 2018; 15 (148): 20180441 DOI: 10.1098/rsif.2018.0441
In this study, we explicitly examine the aerodynamics of manoeuvring flight in animals. We studied brown long-eared bats flying in a wind tunnel while performing basic sideways manoeuvres. We used particle image velocimetry in combination with high-speed filming to link aerodynamics and kinematics to understand the mechanistic basis of manoeuvres. We predicted that the bats would primarily use the downstroke to generate the asymmetries for the manoeuvre since it has been shown previously that the majority of forces are generated during this phase of the wingbeat. We found instead that the bats more often used the upstroke than they used the downstroke for this. We also found that the bats used both drag/thrust-based and lift-based asymmetries to perform the manoeuvre and that they even frequently switch between these within the course of a manoeuvre. We conclude that the bats used three main modes: lift asymmetries during downstroke, thrust/drag asymmetries during downstroke and thrust/drag asymmetries during upstroke. For future studies, we hypothesize that lift asymmetries are used for fast turns and thrust/drag for slow turns and that the choice between up- and downstroke depends on the timing of when the bat needs to generate asymmetries.
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