New migration pattern described for ringed plovers: old theories fail as explanation

When finished breeding in south Sweden (study population is at Ottenby), males and females ringed plover depart to different wintering areas. But males go further south, to winter mainly on the Iberian peninsula, while females stay on average 800 km nearer to the breeding site. In birds it is usually the other way around, that males winter closer to the breeding site, often explained by the need of the territory-defending sex (usually male) that have a need to arrive early on the breeding ground and therefore stay the winter closer. In this new study, Linus Hedh and Anders Hedenström describe a new migration pattern, and add a new model that may explain the new findings. Read more at
https://authors.elsevier.com/a/1aG1j57im1nfX

New paper suggests bats save energy from flight in ground effect

In a new paper published in Current Biology, Animal Flight Lab members describe how Daubenton's bats save energy by flight near a surface, such as a water surface where these bats search for food. The saving s were of the order 30%, which is actually more than what was expected from a glider in ground effect.

Span efficiency of swifts

In a new paper by Per Henningsson and co-workers the span efficiency of swifts flying by flapping and gliding flight, respectively, are analysed. Somewhat counter to intuition the swifts were more efficient during flapping flight than during gliding flight. The reasons for this are discussed in the paper, which is published open access in Plos Biology.

New paper about Leading Edge Vortices in a moth

The first study of the flow above the wings of a freely flying insect, showing the structure of the lift boosting leading edge vortex, is published today by the Animal Flight Lab in Scientific Reports. The leading edge vortex is generally seen as a stable vortex, attached to the top surface of the wing, but this new study finds it to have a complex structure. At the inner wing the vortex has a single core, but mid wing and outwards the vortex is highly variable with multiple simultaneous cores. The highly variable flow may affect the aerodynamic control of the moth. In addition to the high complexity, the circulation of the vortex on the outer part of the wing is higher than the circulation measured in the wake behind the animal. This implies that the vortex accounts for the entire lift production at the outer wing and is in fact stronger than is necessary to generate the required lift force, which suggests a high aerodynamic cost of flight in the moths. These new findings will serve as a baseline comparison for past and future studies of the aerodynamics of insect flight based on tethered animals and mechanical flappers.

Composite image of a representative vector field, color coded by vorticity, showing the complex leading edge vortex above the wing on top of a photo of a Hummingbird hawkmoth (Macroglossum stellatarum)

Money money money

A great day for Animal Flight Lab as both Christoffer Johansson and Per Henningsson bagged research council grants for their research! This means excellent opportunities to carry out research of highest quality the coming 3-4 years. Per has just returned from a 3 year postdoc in Oxford, where he studied insect flight with Richard Bomphrey, will now get the opportunity to become established as a researcher. He will develop comparative studies of maneuvering flight between insects birds and bats, while Christoffer will aim at understanding more about the aerodynamic control of flight.

Congratulaitons!

Update from Brown about bat flight

Last Friday AFL alumni Rhea von Busse visited and gave a talk about her postdoc work at Brown University. Rye Waldman, also at Brown, also presented his work on flow visualization using dual plane light sheets and his work on the aerodynamics of compliant membranes. Rhea showed some really nice X-ray films of flying bats. These experiments nicely showed the movements of the wing skeleton during flight. Rhea also showed that bats can swim, but if they really liked it was not apparent from the footage.

Rye Waldman and Rhea von Busse.

Rye Waldman explains a wake.

New blue thing

As we are waiting to get the laser fixed a new shiny blue storing cabinet arrived. This will help us keep track of all the auxiliary equipment, such as lenses and manuals that now populate all other spaces in the control room to the wind tunnel. Here we can se it be assembled and put into place.

An intelligence test: the locking mechanism is put into function
Up to the right a female common scooter can be seen.

New paper on flight speeds of birds

When we wish to calculate how far a bird can migrate given a certain fuel load, or how fast a bird is expected to fly in a specific context (such as display, foraging or migratory flight), we often make use of flight mechanical theory. The backbone of this theory is the U-shaped relationship between power required to fly and the flight speed through the air (airspeed). The theory was developed/adapted for bird flight more than 40 years ago by the English scientist Colin Pennycuick. Over the years Colin has amended the theory by various experiments and measurements, often involving wind tunnels. Accurate predictions from this theory rely on a number of parameters that describe the aerodynamic properties of the avian body and the wings. Some of these parameters, the induced drag factor and the body drag coefficient, have now been explored in the light of new measurements of flight speeds using an ornithodolite. It turns out that birds are probably more efficient in generating the lift than previously assumed, and also that the body drag coefficient (describing how much drag the body is generating) may vary among species. The fieldwork for this study was carried out last autumn by CAnMove scientists together with Colin Pennycuick, who is at Bristol University, using a new ornithodolite consisting of a Vector range finder (a pairs of binoculars with a laser range finder), an anemometer for wind measurements and a computer for data recording. The fieldwork was carried out on the south east coast of Öland during the autumn migration period in 2012, where large numbers of a variety of species migrated. The paper is published in the Journal of Royal Society Interface, and is open access.

Hummingbird aerodynamics

Todays lab meeting was fully devoted to hummingbird aerodynamics. Firstly, Marta Wolf, who has just returned from a 2-year postdoc in the flight lab at Berkeley University presented her fascinating results from studies of Anna's hummingbird. We learned a lot about how it is to work with hummingbirds, which seems to be easy on one hand but also difficult as birds mass is only about 4.5 g (like a rather lean goldcrest) and they can rapidly loose weight and may have to be released. Marta showed PIV data on the hovering wake, as well as nice illustrations about hummingbird hovering in a box.
Second on todays agenda was the paper from the Altshuler lab about the hovering wake in hummingbirds, which was published i Experiments in Fluids during the last week. The authors claim their data show that the wake consists of bilateral vortex loops, one shed from each wing. In this sense the hummingbird wake show similarities to the typical wake of bats. However, we had some difficulties on seeing what the authors could see in their smoke visualization movies, while we will have reason to return to these data.

Cleaning up and some nostalgia

An old TV monitor is removed

Organization is restored

The old optic rail

Laser optics from MG

Space under test section where the PIV
laser used to live

Yesterday, Friday,  all Lundian members of the lab spent most of the day cleaning and tidying up in the wind tunnel. The reason is that we will soon get new PIV equipment and we need to free space around the test section in order to accommodate the new laser and camera set-ups. We also took the opportunity to clean out and organize the "control room" (the wind tunnel lab office), where lots of computers and monitors have accumulated over the years, which are not used anymore. The biggest operation was the removal of our first PIV laser, a 10 Hz rep rate pulsed laser from Spectra Physics. This laser has served us well and was instrumental to our first custom-built PIV system  that resulted in the first DPIV study of a live animal in free flight (Spedding, Rosén and Hedenström 2003, J Exp Biol). The same laser stayed with us when we replaced the two-camera system with one camera, which we used for our first PIV study of bat flight (Science 2007). After that we have used a stereo-PIV system and Litron laser of 200 Hz. Now it is time to get the 3rd PIV laser to the Lund wind tunnel, and we are grateful to the old equipment that has worked so well over the years. Especially the Spectra Physics laser has been very reliable, but at 10 Hz it is time for retirement. We also removed the rail of mirrors and light sheet optics from Melles Griot, which has been replaced by modern optic arms attached directly to the laser.

Flight Lab 2013 initial efforts

The transition into 2013 has involved a well deserved holiday for members of the Animal Flight Lab, and we have now gathered  gain to resume activities. The Tuesday lab meetings are now populated by two more people than has been the rule the last year. Marta Wolf has returned back from her postdoc at Berkeley, California, and will now join us again, initially on her repatriation funds. Anders attended the annual meeting of the KTH Linnaeus FLOW centre, where he gave a talk about the research we have carried out over the last decade or so. After the meeting he visited the low turbulence windtunnel at the Department of Mechanics (see picture), where research on flow transition is a current point in focus.

Today the entire group made a joint effort to move the boxes containing the laser for our new PIV system. As last time we encountered some problems in getting the large and heavy wooden boxes into the wind tunnel building, but we completed with success. The image shows when we rejected the first method of getting the power supply in through the side door, an attempt that was abandoned in favour of the more direct route through the basement floor after having unpacked the box.

Kinematics and wing shape in flying bats: new paper from the lab

In a new study, originating from Rhea von Busse's PhD thesis, the kinematics and wing shape changes are analyzed in great detail in flying bats, Leptonycteris yerbabuenae. The movements of a great number of morphological landmarks on the wings were analyzed and interpreted with respect to aerodynamic output by the wings. For example, the wing area, angle of attack and camber of the wing all decrease as flight speed increases. This is reflecting the declining demands on the wings as force generating devices. It appears that kinematics change in ways to preserve a favorable flow regime around the wings. However, it remains to investigate how the bats gauge the flow above the wings and use that information to control the motor output, something that we hope to address in future experiments. The paper is published in the open access journal Biology Open.

Animal Flight Lab meets Prof. Marianna Braza

The lab was visited by Prof. Marianna Braza from the Institut de Mécanique des Fluides de Toulouse, France, who presented her research on smart wings and turbulence of airplane landing gears. Marianna has become interested in biomimetics, i.e. obtaining design solutions from nature, with special emphasis on bird wings and ailerons. We presented out work on animal flight and dissuasions were initiated about possible future projects involving bird-inspired aerodynamic solutions, hopefully some that can become useful for future airplane designs.

Autumn lab meetings have started

The members of the Animal Flight Lab at Lund are gathering for the autumn term, which is filled with activities. Our Tuesday morning meetings have resumed and on the last occasion a new paper from the Brown bat flight group was discussed. This paper, by Iriarte-Diaz et al, published in PLoS One, was about "Kinematics plasticity during flight in fruit bats: Individual variability in response to loading", showed that individual bats of the same species has different ways of modulating wing shape and kinematics to achieve increased lift as a response to loaded flight. There are many ways how to achieve increased lift coefficient, such as changing flap frequency, amplitude, wing area and camber, to mention a few. The Brown paper showed that three bats used different combinations of lift enhancing modulation. The group found this paper very interesting!

We will continue to publish updates about lab activities at this site, so stay tuned and you will receive interesting news coming soon, such as reports from field work that starts next week.

Birds Best Bats In Flying Game

The scientific news site LiveScience wrote a cool piece on one of our recent publications (Comparing Aerodynamic Efficiency in Birds and Bats Suggests Better Flight Performance in Birds, PLoS ONE). The title of the piece is 'Birds Best Bats In Flying Game', and particularly their summary is entertaining: 'The bats may be trading some of their flying efficiency to carry extra echolocation equipment aboard'.

You can find the article here.

New publicatiions from the wind tunnel

Two new publications have recently been published from members of AFL. They are:

Johansson LC, Engel S, Baird E, Dacke M, Muijres FT, Hedenström A (2012) Elytra boost lift, but reduce aerodynamic efficiency in flying beetles. J R Soc Interface: doi:10.1098/rsif.2012.0053

Muijres FT, Johansson LC, Bowlin MS, Winter Y, Hedenstrom A (2012) Comparing Aerodynamic Efficiency in Birds and Bats Suggests Better Flight Performance in Birds. PLoS ONE 7(5): e37335. doi:10.1371/journal.pone.0037335

The first shows how the elytra and functional wing in a species of large African dung beetle interact, and potentially reduce flight efficiency. The second paper is also about efficiency, but comparing birds with bats to show that birds are more efficient at cruising flight than bats, while bats may be better adapted for slow maneuvering flight using leading edge vortices.

Informal seminar in Animal Flight Lab

Yesterday, on 14 May 2012, we were visited by long-term collaborator Geoff Spedding and PhD student Shanling Yang, both at USC, Los Angeles. Shanling presented their recent work on low Re aerodynamics of wings, Marco Klein Heerenbrink presented his work on gliding flight and Jonas Håkansson showed the hovering wake of a bat. The wind tunnel was inspected, as was the usual lunch pizza place.

Flycatchers boost lift by Leading Edge Vortex

In a new study, published online today (14 March 2012) in Biology Letters, our lab shows that the high-lift mechanism Leading Edge Vortex (LEV) appear to be common to most animal flyers, as it appears in slow flying pied flycatchers. These birds hover and fly slowly when foraging on aerial insects, and they have a powerful downstroke when the LEV boost the lift by 100%. This is much stronger than found in for example hummingbirds, but that could be explained by the fact that the flycatcher has a feathered (inactive) upstroke. As flycatchers catch insects they need to be equally good at maneuvering in the air, and the LEV helps them to achieve the required turn radii. This mechanism was thought to be restricted to insects, as it was key to explaining why e.g. a bumblebee can fly, and subsequently our group has found this in slowly flying bats. Now, we extend the set of animas using LEV in slow flight to include also normal hoverers (i.e. animals having an inclined stroke plane and inactive back-/upstroke) in this spectacular study.

New wake study of a bat from Brown university

In a new study, published on-line in the Journal of the Royal Society Interface, the Brown University group report on wake measurements from the Brazilian free-tailed bat (Tadarida brasiliensis), using the PIV technique in a wind tunnel (Hubel et al.). This species differs in morphology and ecology from previously studied bat species, having higher aspect ratio wings and mainly flying in he open airspace when feeding on insects. So, does that make it's wake and aerodynamic properties different from other bats? The answer is "no"! Even if the authors argue that the Brazilian free-tailed bat has a wake very similar to that of the swift (Apus apus), it shows all of the characteristic wake features previously observed in bats. These include wing-root vortices and revers-vortices shed at the end of the upstroke. According to the authors when comparing the new data with previously studied bats: "the structure of their wakes is remarkably similar". Hence, it seems as if the notion of a typical "bat wake" receives support from this new study. Further studies will hopefully answer what features of the bat design make bat wakes different from those of birds.

Sized by the wingbeat

The heaviest bat has a body mass of about 1.5 kg, which is about 10 times lower than the largest living bird species. Why this is so has puzzled scientists working on flight mechanics, since the power requirements increase approximately equally much for bats and birds. The solution lies in the muscular capacity in generating forces that beat the wings in active flight. While birds have one major depressor muscle responsible for a forceful downstroke, bats have several smaller muscles doing that same job. But the total muscle mass is smaller in bats, resulting in a lower maximum wingbeat frequency. When plotting scaling relationships for expected power required to fly, and power available from the flight muscles, it turns out that the power available curve (calculated on the basis of wingbeat frequency) does not increase as steeply as that of power required for flight. Where the two curves cross when plotted against body mass, you have the point of maximum mass for sustainable flight. In bats, this is about 1.5 kg, as shown in a new paper by Ulla Lindhe Norberg and Åke Norberg, of Gothenburg university, published in Journal of Experimental Biology. The same analysis was made earlier by Colin Pennycuick, which fixed the upper size sustained bird flight at about 12 kg. It seems as if birds have more muscle power allowing bigger size than bats. A question that follows is whether the basic bat design, having many flight muscles, prevent evolution of large size than about 1.5 kg, or if there are some additional factors limiting size?