The anti-icing tricks of #penguins

Date:

November 23, 2015

Source:

American Physical Society's Division of Fluid Dynamics

Summary:

Antarctic penguins live in a bitterly cold place, where the air temperature can drop to -40 degrees Celsius and the winds can hurtle at speeds of 40 meters per second. Although these birds routinely hop in and out of the water in sub-freezing temperatures, they manage to keep ice from coating their feathers. Now researchers have examined penguin feathers in extreme detail and think they know the penguins' anti-icing trick: a combination of nanostructures and a special oil make Antarctic penguin feathers ultra-water-repelling, or superhydrophobic.

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Diving penguins (Antarctica).

Credit: © alekseev / Fotolia

 

Antarctic penguins live in a bitterly cold place, where the air temperature can drop to -40 degrees Celsius and the winds can hurtle at speeds of 40 meters per second. Although these birds routinely hop in and out of the water in sub-freezing temperatures, they manage to keep ice from coating their feathers.

Now researchers have examined penguin feathers in extreme detail and think they know the penguins' anti-icing trick: a combination of nanostructures and a special oil make Antarctic penguin feathers ultra-water-repelling, or superhydrophobic. Droplets of water on the feathers bead up so much that's it's difficult for heat to flow out of the droplet, and the water will roll off before it has time to freeze.
The researchers will present their findings at the annual meeting of the American Physical Society's Division of Fluid Dynamics, held Nov. 22-24 in Boston, Mass.

Pirouz Kavehpour, a professor in the Department of Mechanical and Aerospace Engineering at UCLA, first got interested in penguin feathers while watching a nature documentary on the famous black and white birds. "I noticed the penguins were coming out of very cold water, and sitting in very cold temperatures, and it was curious that no ice formed on their feathers," he said.

Kavehpour got in touch with Judy St. Leger, a world expert on penguins, who confirmed that indeed no one had ever observed ice on the feather coat of healthy penguins. To find out what the penguins' anti-icing secret was, the two scientists and their colleagues studied penguin feathers, donated by San Diego SeaWorld, using Scanning Electron Microscopy.

They discovered that the feathers had tiny pores that trap air and make the surface hydrophobic. In addition, the penguins apply an oil, which is produced by a gland near the base of their tail, to their feathers. The combination of the nano-sized pits and the preen oil makes the feathers superhydrophobic.

On superhydrophobic surfaces, water droplets bead up and sit on the surface almost like spheres. Kavehpour and his colleagues propose that it's the sphere-like geometry that delays ice formation, since heat has a hard time flowing out of the water droplet if the droplet does not make much contact with the surface.

"Heat flow could be compared to traffic. If you have a freeway that turns into a tiny, two-lane road, the traffic will back up. Similarly, heat does not flow well from the large cross-section of the middle of the drop to the small cross-section where the drop makes contact with the feather," Kavehpour said.

The scientists looked most extensively at the feathers of the gentoo penguin, which lives in Antarctica and the southern-most parts of South America. They also compared the gentoo feathers to feathers from the Magellanic penguin, which lives in warmer climates farther north in Chile, Argentina and even Brazil. They found that the warmer weather penguins lacked the small pores on their feathers, and that the birds also produced a different type of preen oil that was not as hydrophobic.

Penguin's anti-icing solutions could help humans solve some of our own problems with ice. For example, ice on an airplane's wings, flaps and rudder can alter the aerodynamic properties of the plane and even cause it to crash. Airlines spend lots of time and money applying chemical de-icers to planes that fly in winter weather. Superhydrophobic surfaces inspired by penguins might be cheaper, longer-lasting and more environmentally friendly.

"It's a little ironic that a bird that doesn't fly could one day help airplane fly more safely," Kavehpour said.

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Story Source:
The above post is reprinted from materials provided by American Physical Society's Division of Fluid Dynamics. Note: Materials may be edited for content and length.

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American Physical Society's Division of Fluid Dynamics. "The anti-icing tricks of penguins." ScienceDaily. ScienceDaily, 23 November 2015. <www.sciencedaily.com/releases/2015/11/151123103844.htm>.

 

 

Ice Loss Benefits Adélie Penguins—For Now

New research that may presage effects of climate change on this species looks back 22,000 years, finding robust growth in the East Antarctic population as melting followed the last ice age.

Over the past 14,000 years, Adélie penguin numbers in East Antarctica increased 135-fold because of disappearing glaciers and sea ice. The red staining is a mixture of mud and bird guano. Credit: Louise Emmerson

By Cody Sullivan 19 November 2015
 

Antarctic glaciers and sea ice may shrink as global temperatures rise, but Adélie penguins can thrive in a less icy Antarctic landscape, a new study indicates. By determining probable population levels of the birds as far back as 22,000 years ago, the research has revealed that the numbers of East Antarctic Adélie penguins swelled in the past 14,000 years.

The birds’ abundance grew pretty much in reverse proportion to the decline of Antarctic glacial and sea ice as the Earth thawed from its last ice age. Adélie penguins live along much of Antarctica’s coast, but over the past 14,000 years, the East Antarctic population increased 135-fold, reports Jane Younger, who was at the University of Tasmania, Australia, at the time of the study, and her colleagues. The team published its findings yesterday in BMC Evolutionary Biology.

Less Ice Means More Penguins

Adélie penguins need three environmental conditions to flourish: “They need ice-free terrain for their nests, they need open water access to their beaches, and they need a consistent food supply so they can forage and return to their colonies,” said Steven Emslie, an ornithologist from the University of North Carolina, Wilmington, who was not involved in this study. East Antarctica met those conditions as glacial ice retreated inland and sea ice melted from penguin foraging grounds. But regional variability meant that Adélie penguins in other parts of Antarctica didn’t benefit from climate change in the same way.

The many-fold increase in Adélie penguin numbers in East Antarctica isn’t constrained to the past few decades when humans ramped up their rate of forcing greenhouse gases into the atmosphere. The researchers used mitochondrial DNA from 56 living penguins to retrace the birds’ demographic history for the past 22,000 years. They determined that up until about 15,000 years ago, there were fewer than 1000 East Antarctic Adélie penguins. However, as conditions improved for the penguins there, other penguins from the Scotia Arc may have migrated over and bolstered the East Antarctic population. After that, the Adélie penguin population on East Antarctica increased in line with a general deglaciation trend as the Earth emerged around that same time from its last global glaciation.
In the past 30 years, as climate change ramped up and conditions continued to improve for the penguins, the Adélie population nearly doubled. Scientists estimate the current Adélie population at around 1.14 million breeding pairs, with 30% of them coming from the East Antarctic region.

Continued Growth Is Unclear

Even though the East Antarctic Adélie penguin population has grown abundantly, that doesn’t necessarily mean the population will continue to do so. Scientists don’t know how the penguin’s prey, Antarctic krill, will react to warming temperatures, and the temperatures might become too warm for the penguins themselves. “The warming trend does reach a threshold where it can be beneficial at first but then start having negative impacts,” said Emslie, who has already seen negative effects on Adélie penguins in his own research along the Antarctic Peninsula. The new study provides rare insight into how an animal population reacts to climate change on a millennial time scale, in contrast to a more recent decadal scale. “I think it’s important to realize that the climate change that’s happening now is not a short-term kind of thing. It’s a real change in the climate that’s going to last thousands of years,” said Younger, the study’s lead author, who is now at Loyola University in Chicago, Ill.

 

“If we want to really think about the effects of climate change on these animals, we need to think about not just how they’re going to be affected in the short term, but how they’re going to be affected in the long term as well. And that’s where these millennial-scale studies into the past can help.” —Cody Sullivan, Writer Intern

Citation: Sullivan, C. (2015), Ice loss benefits Adélie penguins—For now, Eos, 96, doi:10.1029/2015EO040059. Published on 19 November 2015.

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Shrinking Antarctic glaciers could make Adélie penguins unlikely winners of climate change

November 17, 2015 

 

 

Adélie Penguins struggle to reach their nesting sites if there’s too much ice in the way. Jane Younger, Author provided

Author: Jane Younger

Postdoctoral research fellow, University of Tasmania

Disclosure statement

Jane Younger receives funding from the Australian Antarctic Division, the ANZ Trustees Holsworth Wildlife Research Endowment, the Sea World Research and Rescue Foundation, and the National Science Foundation.

Partners

University of Tasmania provides funding as a member of The Conversation AU.

Penguin numbers exploded in East Antarctica at the end of the last ice age, according to research published today in BMC Evolutionary Biology. Despite their image as cold-loving creatures, the increase in Adélie penguin numbers seems to be closely linked to shrinking glaciers, raising the possibility the these penguins could be winners from current climate change.

Adélie penguins are one of only two penguin species that live on the Antarctic continent. Their cousins, emperor penguins, may be the movie stars, but it is the Adélies that are the bigger players in the Southern Ocean. They outnumber emperors by more than ten to one, with a population of over 7.5 million breeding adults and counting.

Given the abundance of Adélie penguins and their crucial role in Southern Ocean ecosystems, there has been a great deal of interest in understanding how the species is likely to respond to future climate change.

There are more then 7 million of these guys in Antarctica. Jane Younger, Author provided

Sensitivity to sea ice

Breeding colonies have been monitored for decades to determine the effects of a changing environment on the penguins. A common finding of many of these studies is that Adélies are highly sensitive to sea ice conditions.

Unlike emperor penguins, Adélies do not nest on the sea ice, but they must cross it to reach their nests on land. As everyone knows, penguins are not the most efficient walkers, and in years with a lot of sea ice their journeys to and from the ocean to feed their chicks can become lengthy. With a longer wait between meals chicks are less likely to survive.

In an extreme case, extensive sea ice at one breeding colony had a devastating impact in 2014, and not a single chick survived.

Based on these observations over years and decades, there has been concern that changing sea ice conditions, including increases in certain parts of Antarctica, could have a serious impact on Adélie penguin numbers in the future.

Short-term vs long-term climate change

However, the climate change that is taking place now is not a decadal trend. Rather, the shrinking glaciers and ice sheets, changing sea ice conditions, and shifting currents and weather patterns represent a global change to a new climate.

We therefore set out to understand how Adélie penguins in East Antarctica were affected by the last big shift to a different climate: the ending of the last ice age.

Following similar methods to our previous study on emperor penguins, we used genetic data to uncover the trend of the Adélie population in East Antarctica over the past 22,000 years.

Researchers have been investigating penguins to see how they might respond to climate change. Laura Morrissey, Author provided

The end of the ice age

We found that, as for the emperor penguins, Adélies were far less common during the ice age. This is not at all surprising since most of their nesting sites would have been covered with glaciers and their feeding grounds encased in sea ice that never melted.

Following the end of the ice age 20,000 years ago, temperatures increased slowly, and after a few thousand years of warming the glaciers and ice sheets began to shrink. Fast forward to 10,000 years ago and the annual sea ice melting cycle that we see today was established.

Given the sensitivity of Adélie penguins to sea ice changes today, we predicted that Adélie numbers would remain very small until 10,000 years ago when sea ice conditions became similar to what they are now.

However, the penguins surprised us again. We found that the number of Adélies exploded by around 135-fold, but the expansion pre-dated the sea ice change by at least 3000 years.

Penguin numbers exploded at the end of the last ice age. Jane Younger, Author provided

Shrinking glaciers

The proliferation of Adélie penguins in East Antarctica began during a period of ice sheet and glacier retreat, which would have increased the amount of ice-free ground available for nesting.

A study of Adélie penguins at the Scotia Arc, on the opposite side of the continent, found that numbers in this region rose 17,000 years ago. That expansion was several thousand years before the growth of the East Antarctic population, but coincided with the shrinking of glaciers in the Scotia Arc. This lends further support to our conclusion that it was glacier retreat, rather than changing sea ice conditions, that caused the hike in Adélie penguin numbers after the last ice age.

This is an important finding, as it suggests that the effects of climate change on a species over thousands of years can be quite different to the effects over years or decades. Given the long-term nature of contemporary climate change, we suggest that it is critical to consider millennial-scale trends alongside decadal ecological studies when predicting the effects of climate change on a species.

Could penguins benefit from future climate change?

Glaciers and ice sheets in Antarctica will continue to shrink. As this happens, ground that was previously covered in ice will become suitable for Adélie penguin nesting. In regions with adequate food supplies and where sea ice conditions remain favourable, Adélie penguin numbers may continue to grow.

A recent study using satellite images showed that one breeding colony in the Ross Sea grew by 84% between 1983 and 2010, as a direct result of a glacier shrinking by 543 m and uncovering new nesting sites.

While it seems that East Antarctic Adélie penguins might come out on top as climate change winners, it is important to keep in mind that for penguins to flourish their food supplies must be plentiful enough to meet the demands of a growing population. Whether this will be the case in the future remains to be seen, as Adélie penguin prey species, such as Antarctic krill, are threatened by both climate change and commercial fisheries.

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The dinosaur ankle re-evolved amphibian-like development in birds

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Date:

November 13, 2015

Source:

Universidad de Chile

Summary:

In the 19th century, Darwin's most vocal scientific advocate was Thomas Henry Huxley, who is also remembered as a pioneer of the hypotheses that birds are living dinosaurs. He noticed several similarities of the skeleton of living birds and extinct dinosaurs, among them, a pointed portion of the anklebone projecting upwards onto the shank bone (aka drumstick). This "ascending process" is well known to specialists as a unique trait of dinosaurs. However, until the late 20th century, many scientists were doubtful about the dinosaur-bird link. Some pointed out that the ascending process in most birds was a projection of the neighbouring heel bone, rather than the anklebone. If so, it would not be comparable, and would not support the dinosaur-bird link. 

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Like modern amphibians, the remote ancestors of birds once had three bones in their upper ankle. When these evolved into landegg-laying animals, only two bones were present in this region. In dinosaurs, one of these, the anklebone, presents a pointed upward projection, the "ascending process". This trait is also present in birds, which are living dinosaurs. A new detailed embryological study in birds reveals that their ankle has re-evolved an amphibian-like developmental pattern, with three separate elements, one of which becomes the dinosaurian ascending process

Credit: Image courtesy of Universidad de Chile

 

In the 19th century, Darwin's most vocal scientific advocate was Thomas Henry Huxley, who is also remembered as a pioneer of the hypotheses that birds are living dinosaurs. He noticed several similarities of the skeleton of living birds and extinct dinosaurs, among them, a pointed portion of the anklebone projecting upwards onto the shank bone (aka drumstick). This "ascending process" is well known to specialists as a unique trait of dinosaurs. However, until the late 20th century, many scientists were doubtful about the dinosaur-bird link. Some pointed out that the ascending process in most birds was a projection of the neighbouring heel bone, rather than the anklebone. If so, it would not be comparable, and would not support the dinosaur-bird link.

Some argued that in bird embryos, the ascending process develops from the anklebone in dinosaur-like fashion, while others considered that its development in birds is unique and different from dinosaurs. Nowadays, the dinosaur-bird link is mainstream science, thanks to new methods of data analysis, and a dense series of intermediate fossils (including feathered dinosaurs). However, the disagreements about the composition and embryology of the avian ankle were never clarified fully. A new study in Nature Communications by Luis Ossa, Jorge Mpodozis and Alexander Vargas, from the University of Chile, provides a careful re-examination of ankle development in 6 different major groups of birds, selected specifically to clarify conditions in their last common ancestor. It also utilizes new techniques that allow three-dimensional analysis of fluorescent embryonic skeletons, using advanced spin-disc confocal microscopy and software.

This work has revealed that the ascending process does not develop from either the heel bone or the ankle bone, but from a third element, the intermedium. In the ancient lineage of paleognath birds (such as tinamous, ostriches and kiwis) the intermedium comes closer to the anklebone, producing a dinosaur-like pattern. However, in the other major avian branch (neognaths), which includes most species of living birds, it comes closer to the heel bone; that creates the impression it is a different structure, when it is actually the same. "It puts the final nail in the anti-dinosaur coffin" says Jacques Gauthier, a vertebrate paleontologist and professor at Yale University "The dinosaurian ascending process is retained in all birds, though it has changed its association from ankle to heel bones in neognath birds."

More remarkably, however, this finding reveals an unexpected evolutionary transformation in birds. In embryos of the landegg-laying animals, the amniotes (which include crocodilians, lizards, turtles, and mammals, who secondarily evolved live birth) the intermedium fuses to the anklebone shortly after it forms, disappearing as a separate element. This does not occur in the bird ankle, which develops more like their very distant relatives that still lay their eggs in water, the amphibians. Since birds clearly belong within landegg-laying animals, their ankles have somehow resurrected a long-lost developmental pathway, still retained in the amphibians of today -- a surprising case of evolutionary reversal. The study also presented fossil evidence from juvenile specimens of toothed birds from the Cretaceous period. These show that, at this early stage of bird evolution, the ascending process already developed separately.

Evolutionary reversions have always generated much discussion among scientists, because ancient traits can occasionally re-appear in a highly transformed context. A recent paper in BMC Evolutionary Biology (Diaz and Trainor, 2015) has revealed that chameleons also re-evolved an independent intermedium, in the specialized functional context of a climbing reptile. The reappearance of this long-lost developmental pattern in highly evolved organisms like birds and chameleons could be compared to finding primitive clockwork gears inside your latest smartphone. These intriguing discoveries are bound to renew discussion about the interplay between the evolution of new functions and the resurrection of old developmental patterns.

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Story Source:
The above post is reprinted from materials provided by Universidad de Chile. Note: Materials may be edited for content and length.

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Journal Reference:

1. Luis Ossa-Fuentes, Jorge Mpodozis, Alexander O Vargas. Bird embryos uncover homology and evolution of the dinosaur ankle. Nature Communications, 2015; 6: 8902 DOI: 10.1038/ncomms9902

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Universidad de Chile. "The dinosaur ankle re-evolved amphibian-like development in birds." ScienceDaily. ScienceDaily, 13 November 2015. <www.sciencedaily.com/releases/2015/11/151113105924.htm>.

Flying under the radar: Seabirds hold the key to healthy fisheries

Seabirds are being severely threatened by fisheries, pollution and invasive species. Scientist and conservationalist Ross Wanless explains to DW why the birds of the sea could be pivotal for survival of the planet.

The African-Eurasian Waterbird Agreement (AEWA) met in Bonn, Germany, November 9 through 13 to discuss conservation of seabirds. In addition to aiming for an agreement from AEWA member countries on changing fishery management to benefit migratory seabirds, researchers and conservationists also worked together on managing other seabird threats.

DW caught up with Ross Wanless of BirdLife International toward the end of the conference in Bonn.

DW: What is the state of seabirds globally?

Ross Wanless: Seabirds are among the most threatened group of birds in the world, in fact their conservation status has decreased faster than any equivalent group of birds, so they are really not in good shape.

What is the biggest threat to seabirds?

There are two main threats, one is fisheries and a whole range of things within that - so accidental mortality and overfishing - and the other is invasive species on islands.

About 30 years ago, people discovered that when they counted up the number of birds that had been caught up in tuna longline fishing hooks and extrapolated that to the whole fishery, they realized that one or two birds on each boat every day translated into tens of thousands of albatrosses. That broke open a huge issue that we have been battling with ever since: how to stop birds from being caught on longlines.

Solving the problems of seabird conservation, Wanless says, is not an easy job

What, if any, solution exists to address the impact of fisheries on sea birds?

There are many solutions, some of them are quite simple and straightforward, don't cost a lot and allow fishing to continue really essentially unchanged. Like just minor modifications to their gear, or how fishers work.

There are other, probably more problematic solutions, such as reduction in fishing and area closures to fishing. There is a whole suite of things that can be done.

If we focus on your home country, South Africa, what would you say is needed there to help seabirds?

BirdLife South Africa has done some amazing work in preventing bycatch, or the incidental catching of seabirds in our fisheries, and our fisheries are some of the best in the world in terms of having solved these enormous problems almost completely.

But, we're really grappling with the problem of the lack of food and the role that fisheries play in causing the collapse of, for example, African penguin populations. So, while we have been good at solving some problems, we are still really coming to grips with some of the other problems.

Through your work, you have initiated some large-scale conservation programs to help the African penguin and other seabirds at risk of low trophic level fisheries impacts, what has that entailed?

Low trophic level fisheries, or forage fisheries, are fisheries that target the small things in the sea, like krill, or sardine or anchovy. They tend to be at the base of the ecosystem, the base of the food chain, so if you overfish those stocks, everything else that feeds on them - the whales, the dolphins, the seals, the seabirds, the other fish that are also commercially exploited - all take strain. It's a real problem and that's the kind of fishing we have to manage very carefully, and that is what we think is behind some of the African penguin collapse.

We need to look at seabirds to understand how other marine life are faring, says Wanless

There is no question that overfishing happened in our waters in the 1960s. The stocks of fish have changed dramatically, and the penguin numbers collapsed along with that.

How can people live harmoniously with seabirds? 

I think to many people, there is a false dichotomy. It's not seabirds or fisheries - actually, fisheries should be using seabirds. We believe that penguins, for example in the southwestern part of Africa, are a real sentinel: They are a signal that the marine system is under stress and that if we don't pay attention, the fisheries could collapse.

What we are trying to convince people is: Use the penguins, the information they are telling you is valuable, and you should maybe think seriously about changing your fishing practices.
Pitting penguins or other seabirds against fisheries is really the wrong way to look at it. When the penguins recover, you will probably have a healthy ecosystem again.

I challenge you to answer the question "how many fish are in the sea" with any degree of accuracy - but I can tell you exactly how many penguins there are in southern Africa. We have really good data that we can use, and if we could just change our mindset about that, I think everyone would be in a better space.

The average person may possibly say "seabirds don't concern me" - why should we care about them? 

Seabirds in many respects are an important tool for helping manage our impact on the marine environment. The interconnectedness of the ocean is dynamic and different from terrestrial environments, and we don't really have a good understanding or ability to mange it. If we let the seabirds go, if we forget about them and say we don't care, we can live without them - maybe we are right, maybe we are wrong. If we are wrong, have we lost something we can never recover, and everyone suffers at the end of the day? We are playing a high-risk game by ignoring critical components of ecosystems such as seabirds.

If we destroy those species, future generations will never forgive us - we have a responsibility to look after those things.

Fishers, government and individuals need to work together to ensure seabird survival, Wanless tells DW

What recent developments have been made to protect seabirds? 

Seabirds are probably the most international birds of all birds, because the high seas occupy about 60 percent of the surface of the Earth. No one owns the high seas, so they are not in any one country's waters for much of their lives. So we have to be joined up and work collaboratively to protect them.
We have created the World Seabird Union, which brings together 90 percent of seabird

conversationalists and researchers, and that gives us a united voice where we can discuss and plan around issues and hold conferences. This allows us to pull things together in a joint way that is so much more powerful than people or countries working individually.

What has come out of the Bonn conference?

The conference has really shown the willingness of countries to grapple with issues and to find effective, efficient ways of addressing problems - not duplicating existing initiatives or existing programs - and that is really encouraging.

That means we are not throwing money at problems. Everyone is really conscious of finding ways where an agreement can be used to do things that no one else is doing, and we don't need to bother with where others are doing them - that, to me, is a really encouraging sign.

Dr. Ross Wanless is the Africa Coordinator for the BirdLife International Marine Programme, and the Seabird Conservation Programme manager for BirdLife South Africa.

The interview was conducted by Jessie Wingard.

source

Shape of bird wings depends on ancestors more than flight style

Date:

November 5, 2015

Source:

University of Texas at Austin

Summary:

In a finding that could change the way scientists think about bird evolution, researchers have found that the shape of bird wings is influenced more by how closely related species are to one another than by flight style.The research challenges scientific beliefs that assume the way a bird species flies -- whether it primarily dives, glides or flaps, for instance -- plays the primary role in the evolution of its wing shape.

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Samples of the dorsal (middle column) and ventral (left column) sides of wings from bird specimens analyzed by the researchers. The right column depicts a consensus wing shape generated by analyzing the wing shape of 105 bird taxon (figure f), a figure depicting how various wing shapes differed from the consensus wing (figure g), and the magnitude of variation across different parts of the consensus wing ( figure h). Credit: Xia Wang.

In a finding that could change the way scientists think about bird evolution, researchers have found that the shape of bird wings is influenced more by how closely related species are to one another than by flight style.

The research challenges scientific beliefs that assume the way a bird species flies--whether it primarily dives, glides or flaps, for instance--plays the primary role in the evolution of its wing shape. It also indicates that it may be more difficult than previously thought to infer flying behaviors of early birds and the first flying dinosaurs from fossils alone.

Julia Clarke, an associate professor in the Department of Geological Sciences at The University of Texas Jackson School of Geosciences, conducted the work with Xia Wang, a post-doctoral researcher who led the study. Their research was published in the journal Proceedings of the Royal Society B: Biological Sciences in October.

Bird wings, unlike stiff airplane wings, are flexible and change shape during flight. So, their geometry and wing outline may not tell the whole story of a particular flight style or environment, Clarke said. "We've taken a lot for granted. Birds are not airplanes," Clarke said.

By comparing geometry across species and clades -- groups of organisms that evolved from a common ancestor -- the researchers found that birds that are closely related evolutionarily have similar wing structures, even if the birds show very different flight styles. For example, albatrosses, penguins and loons, despite looking very different from one another, all belong to the clade Aequornithes and have a wing shape that is very similar.

The study is the first to analyze wing geometry across all major groups of birds. Researchers
analyzed over 100 photographs of wings from different bird species.

In general, the analysis of species from across nine major avian clades showed that wing shape became more varied as different clades diverged from early ancestors, Clarke said. The researchers found an interesting exception to this trend in the wings of Passerines --a clade that includes songbirds. Instead of a wing shape that resembles more closely related relatives, their shape resembles that of Galliformes, a distantly related order that includes birds, such as chickens and turkeys, whose direct ancestors were among the first birds on the planet. "Those little songbirds share aspects of wing geometry, especially the relative length of the covert feathers, with some of early bird species but have very different body sizes, ecologies and flight styles," Clarke said.

Clarke and Wang also studied covert feathers in these birds. They found that across clades these feathers, which cover the base of the flight feathers, are about the same length whether they are on the top or underside of a wing. The similarity of covert feathers both on a single wing and across clades, brings into question their function, Clarke said.

It's been proposed that some of the upper coverts may play a sensory role, and the lower or underwing coverts, a role in aerodynamics. But the similarity in the distribution and organization of covert feathers on both sides of the wings suggests that such distinct roles may not be the case, Clarke said. "There's no existing hypothesis to explain that pattern," Clarke said. "So a question now is why the length of these feathers tends to be similar and why they show similar trends across birds. We could be looking for a developmental explanation or a functional one."

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Story Source:
The above post is reprinted from materials provided by University of Texas at Austin. Note: Materials may be edited for content and length.

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Journal Reference:

1. Xia Wang, Julia A. Clarke. The evolution of avian wing shape and previously unrecognized trends in covert feathering. Proceedings of the Royal Society B: Biological Sciences, 2015; 282 (1816): 20151935 DOI: 10.1098/rspb.2015.1935

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University of Texas at Austin. "Shape of bird wings depends on ancestors more than flight style." ScienceDaily. ScienceDaily, 5 November 2015. <www.sciencedaily.com/releases/2015/11/151105103041.htm>.