Drag reduction by air release promotes fast ascent in jumping Emperor Penguins—a novel hypothesis

MEPS prepress abstract  -  doi: 10.3354/meps08868

Drag reduction by air release promotes fast ascent in jumping Emperor Penguins—a novel hypothesis

John Davenport*, Roger N. Hughes, Marc Shorten, Poul S. Larsen

*Email: j.davenport@ucc.ie

 

ABSTRACT: To jump out of water onto sea ice, emperor penguins must achieve sufficient underwater speed to overcome the influence of gravity when they leave the water. The relevant combination of density and kinematic viscosity of air is much lower than for water. Injection of air into boundary layers (‘air lubrication’) has been used by engineers to speed movement of vehicles (ships, torpedoes) through sea water. Analysis of published and unpublished underwater film leads us to present a hypothesis that free-ranging emperor penguins employ air lubrication in achieving high, probably maximal, underwater speeds (mean 5.3 m s^-1, SD 1.01 m s^-1), prior to jumps. Here we show evidence that penguins dive to 15-20 m with air in their plumage and that this compressed air is released as the birds subsequently ascend whilst maintaining depressed feathers. Fine bubbles emerge continuously from the entire plumage, forming a smooth layer over the body and generating bubbly wakes behind the penguins. In several hours of film of hundreds of penguins, none were seen to swim rapidly upwards without bubbly wakes. Penguins descend and swim horizontally at about 2 m s^-1; from simple physical models and calculations presented, we hypothesise that a significant proportion of the enhanced ascent speed is due to air lubrication reducing frictional and form drag, that buoyancy forces alone cannot explain the observed speeds, and that cavitation plays no part in bubble formation.

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Gentoo penguins in a colony: The bird in the middle watches over two chicks and carries a GPS-depth logger which was fixed to the plumage. The tape shows distinct signs of the animal’s most recent dive when the penguin was hunting in more than 100 metres depth. (Credit: Petra Quillfeldt)

How Seabirds Share Their Habitat

ScienceDaily (Jan. 13, 2011) — When different species of seabirds share a habitat with limited sources of food, they must differ in their feeding habits. This specialisation is known by biologists as an "ecological niche." Researchers at the Max Planck Institute for Ornithology in Radolfzell have investigated how flexible these ecological niches really are. They discovered that the preying habits of diving seabirds are very different, both in location and timing, within species as well as between different species.

Ecological niches are not inflexible; they are affected by different habitats and the need to avoid competition with neighbours or evade predators, and also lead to different forms of behaviour within a single species.
Seabirds are an excellent species for studying the question of how animals share the limited supply of food in their habitat. Seabirds must live on land during the breeding season, and over this period they have to share space and food with many other animals. The birds breed in nesting colonies, often in confined spaces that provide protection from predators -- the food supply, however, is widely distributed throughout the sea off the coast. The birds must leave the colony to find food and then return to the islands to feed their chicks.

The scientists wanted to know how several species, similar in their demands, are able to breed together on an island and what exactly the differences in their ecological niches are. Using GPS-depth loggers that allow scientists to track birds detailed in three dimensions, researchers in the past have discovered the hunting areas and depths of several diving seabirds, such as penguins and cormorants, but always only for sample colonies. Until now it has been unknown whether these data can be transferred to entire species.

On New Island, part of the Faulkland Islands in the southern Atlantic Ocean, scientists at the Max Planck Institute for Ornithology used GPS-depth loggers to comprehensively study complete a comprehensive study of the hunting habits of four diving seabirds: three species of penguins -- Gentoo penguins, Rock Hopper penguins and Magellan penguins -- and Imperial shags. In addition, the researchers compared two colonies of each of the three penguin species.

"The results were very surprising," says biologist Dr. Juan Masello. "Based on the ecological niche theory, we had expected especially strong differences between species. However, the data show that the spatial and temporal distribution of birds within the species can also differ greatly."

Magellan penguins, for example, used hunting areas about 40 kilometres apart from each other, whereas the two colonies on land were only two kilometres apart. In contrast, one of the Gentoo penguin colonies often hunted at night, while the other neighboured colony hunted only in the daytime. In this way, the colonies avoid an overlap in feeding areas and small-scale differences are used effectively." adds Dr. Petra Quillfeldt. In the colony of Imperial shags, the females and males hunt both at different times and places: in the mornings, the females go hunting near the coast, and in the afternoons, the males hunt in the open sea. Thus the different species of seabirds found different solutions to avoid competing with their own species for food.

"Of course, food is not the only factor that determines the distribution of birds around the island," Dr. Quillfeldt explains. "In two of the penguin species, it was very clear that the animals avoided swimming near a seal colony where they could themselves become the prey. This dangerous zone also contributed to the spatial separation of the birds in the sea."

This is the first comprehensive study showing the ecological niches within a species, as well as between species, over the same period of time. It shows that seabirds of different species, as well as colonies of the same species, differ in their temporal and spatial distribution and that they search for food in different areas of the ocean, often far apart, and at different depths and temperatures. The ecological niches of the species studied are far less rigid than previously thought. Even small differences in habitat or in behaviour, or the need to avoid competition or predators, contribute to this specialisation.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Max Planck Institute for Ornithology, via AlphaGalileo.

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Journal Reference:

1. Masello, J.F., Mundry, R., Poisbleau, M., Demongin, L., Voigt, C., Wikelski, M. & Quillfeldt P. Diving seabirds share foraging space and time within and among species.. Ecosphere, December 20, 2010 DOI: 10.1890/ES/0-001031

Max Planck Institute for Ornithology. "How seabirds share their habitat." ScienceDaily 13 January 2011. 17 January 2011 <http://www.sciencedaily.com­ /releases/2011/01/110111132213.htm>.

That Controvery Over Flipper Bands

King Penguins. Flipper-banded penguins have a 16% lower survival rate and produce 39% fewer chicks than non-banded birds. (Credit: iStockphoto/Benjamin Goode)

Flipper Bands Hinder King Penguins

ScienceDaily (Jan. 16, 2011) — A team of researchers headed by Yvon Le Maho, CNRS researcher at the Institut Pluridisciplinaire Hubert Curien (CNRS / Université de Strasbourg) and member of the Académie des Sciences, has demonstrated that, over a ten year period, flipper-banded penguins have a 16% lower survival rate and produce 39% fewer chicks than non-banded birds. These results were obtained through electronic monitoring of one hundred king penguins on Possession Island in the southern hemisphere. As a precautionary measure, French researchers have stopped banding penguins since the 1990s.

Supported (1) by the Institut Polaire Français Paul-Émile Victor, this work was carried out in collaboration with Oslo and Tromsø universities in Norway, the Tour du Valat biological station and the Muséum National d'Histoire Naturelle and has been published on 13 January in Nature, also featuring on the cover of the journal.

Penguins are excellent indicators of the state of health of marine ecosystems and thus make it possible to better understand the impact of climate change on biodiversity. As a matter of fact, these top predators of the Southern Ocean are at the summit of the marine food chain. Their population dynamics is thus conditioned by the evolution of marine resources; any modifications arising in their survival and breeding success reflect to a large extent the impact of climate on lower links in the food chain (fish, zooplankton, etc.). Until now, most of the available data has been obtained by banding the animals being monitored. However, unlike other birds, it is impossible for anatomical reasons to fit bands to penguins' feet. Researchers therefore fit them to their flippers. These metal bands can be read at a distance, thus avoiding any stress involved in recapturing the penguins. The use of such flipper bands however raises serious questions as they can have deleterious effects on the animal. These effects include injuring flipper tissues or increasing energy expenditure while swimming or fishing due to the hydrodynamic drag effect on the flippers that the penguins use to propel themselves. Short-term studies (maximum one year) have concluded that banding has no impact. As a precaution, certain researchers, including French teams, have abandoned it but it is still used throughout the world. In addition, some scientists continue to rely on data from banded birds.

For the first time, a French-Norwegian team has conducted a long-term study, the objective of which was to monitor, over a ten year period, one hundred king penguins with electronic tags implanted under their skin, half of which were also fitted with a flipper band. The penguins were identified individually by radiofrequency using antennas buried along their passageways, between the colony and the sea. This electronic monitoring system was developed in 1998 by Le Maho's team at the Institut Pluridisciplinaire Hubert Curien (CNRS / Université de Strasbourg). The researchers focused on two key parameters for monitoring the evolution of this penguin population: their mortality rate and their breeding success. Their results unequivocally prove the significant impact of flipper banding, which affects both the survival and breeding of these animals, in the medium and long term. The banded population's growth rate is a fortiori also affected. In fact, over the last decade, the 50 banded penguins produced 39% fewer chicks (from laying until the chicks can feed for themselves). In addition, their mortality was 16% higher than that of non-banded birds.

The banded birds arrive later at their reproduction sites and, after having been banded for 10 years, they continue to have a delayed breeding cycle on account of their longer foraging trips. This study thus refutes the theory that penguins get used to such bands after a certain time. Another very important result is that banded penguins do not react in the same manner as non-banded penguins to climatic variability (mainly sea temperature). This is why, depending on the year and the environmental conditions, the effect of banding is more or less perceptible. "In favorable periods, when the sea temperature is low and food resources are abundant, there is virtually no difference between banded and non-banded animals," explains Claire Saraux, the leading author of this article. "On the other hand, when the sea temperature is higher, the penguins need to forage further to find their food and banded birds then stay longer at sea." These results thus demonstrate the need for long-term studies to test the possible effects of methods used to monitor animal populations.

From an ethical point of view, this study calls into question the numerous banding campaigns that are still ongoing. These results are obviously specific to penguins and cannot be generalized to foot-banded flying birds. Furthermore, since banded and non-banded penguins do not react in the same way to changes in sea temperature, this study demonstrates that flipper banding introduces an important bias in the study of climatic effect on the dynamics of penguin populations. Since current knowledge of this effect is based to a large extent on data from banded birds, such information must therefore be considered with caution.

(1) This work benefited from the financial and/or logistical support of CNRS, IPEV, TAAFs, the Fondation Bettencourt-Schueller and the Fondation des Treilles.
Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by CNRS (Délégation Paris Michel-Ange), via AlphaGalileo.

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Journal Reference:

1. Claire Saraux, Céline Le Bohec, Joël M. Durant, Vincent A. Viblanc, Michel Gauthier-Clerc, David Beaune, Young-Hyang Park, Nigel G. Yoccoz, Nils C. Stenseth, Yvon Le Maho. Reliability of flipper-banded penguins as indicators of climate change. Nature, 2011; 469 (7329): 203 DOI: 10.1038/nature09630

CNRS (Délégation Paris Michel-Ange). "Flipper bands hinder king penguins." ScienceDaily 16 January 2011. 17 January 2011 <http://www.sciencedaily.com­ /releases/2011/01/110114155243.htm>.

Future Climate for Penguins Discussed

A pair of chinstrap penguins in Antarctica. New research suggests that, if carbon dioxide emissions continue on their current trajectory, Earth may return to a climate of tens of millions of years ago when the Antarctic ice sheet did not exist. (Credit: © UCAR, Photo by Andrew Watt)

Earth's Hot Past Could Be Prologue to Future Climate

ScienceDaily (Jan. 14, 2011) — The magnitude of climate change during Earth's deep past suggests that future temperatures may eventually rise far more than projected if society continues its pace of emitting greenhouse gases, a new analysis concludes.

The study, by National Center for Atmospheric Research (NCAR) scientist Jeffrey Kiehl, will appear as a "Perspectives" piece in this week's issue of the journal Science.
Building on recent research, the study examines the relationship between global temperatures and high levels of carbon dioxide in the atmosphere tens of millions of years ago. It warns that, if carbon dioxide emissions continue at their current rate through the end of this century, atmospheric concentrations of the greenhouse gas will reach levels that existed about 30 million to 100 million years ago, when global temperatures averaged about 29 degrees Fahrenheit (16 degrees Celsius) above pre-industrial levels.
Kiehl said that global temperatures may gradually rise over centuries or millennia in response to the carbon dioxide. The elevated levels of carbon dioxide may remain in the atmosphere for tens of thousands of years, according to recent computer model studies of geochemical processes that the study cites.
The study also indicates that the planet's climate system, over long periods of times, may be at least twice as sensitive to carbon dioxide than currently projected by computer models, which have generally focused on shorter-term warming trends. This is largely because even sophisticated computer models have not yet been able to incorporate critical processes, such as the loss of ice sheets, that take place over centuries or millennia and amplify the initial warming effects of carbon dioxide.
"If we don't start seriously working toward a reduction of carbon emissions, we are putting our planet on a trajectory that the human species has never experienced," says Kiehl, a climate scientist who specializes in studying global climate in Earth's geologic past. "We will have committed human civilization to living in a different world for multiple generations."
The Perspectives article pulls together several recent studies that look at various aspects of the climate system, while adding a mathematical approach by Kiehl to estimate average global temperatures in the distant past. Its analysis of the climate system's response to elevated levels of carbon dioxide is supported by previous studies that Kiehl cites. The work was funded by the National Science Foundation, NCAR's sponsor.

Learning from Earth's past

Kiehl focused on a fundamental question: when was the last time Earth's atmosphere contained as much carbon dioxide as it may by the end of this century?
If society continues on its current pace of increasing the burning of fossil fuels, atmospheric levels of carbon dioxide are expected to reach about 900 to 1,000 parts per million by the end of this century. That compares with current levels of about 390 parts per million, and pre-industrial levels of about 280 parts per million.
Since carbon dioxide is a greenhouse gas that traps heat in Earth's atmosphere, it is critical for regulating Earth's climate. Without carbon dioxide, the planet would freeze over. But as atmospheric levels of the gas rise, which has happened at times in the geologic past, global temperatures increase dramatically and additional greenhouse gases, such as water vapor and methane, enter the atmosphere through processes related to evaporation and thawing. This leads to further heating.
Kiehl drew on recently published research that, by analyzing molecular structures in fossilized organic materials, showed that carbon dioxide levels likely reached 900 to 1,000 parts per million about 35 million years ago.
At that time, temperatures worldwide were substantially warmer than at present, especially in polar regions -- even though the Sun's energy output was slightly weaker. The high levels of carbon dioxide in the ancient atmosphere kept the tropics at about 9-18 degrees F (5-10 degrees C) above present-day temperatures. The polar regions were some 27-36 degrees F (15-20 degrees C) above present-day temperatures.
Kiehl applied mathematical formulas to calculate that Earth's average annual temperature 30 to 40 million years ago was about 88 degrees F (31 degrees C) -- substantially higher than the pre-industrial average temperature of about 59 degrees F (15 degrees C).

Twice the heat?

The study also found that carbon dioxide may have at least twice the effect on global temperatures than currently projected by computer models of global climate.
The world's leading computer models generally project that a doubling of carbon dioxide in the atmosphere would have a heating impact in the range of 0.5 to 1.0 degree C watts per square meter. (The unit is a measure of the sensitivity of Earth's climate to changes in greenhouse gases.) However, the published data show that the comparable impact of carbon dioxide 35 million years ago amounted to about 2 degrees C watts per square meter.
Computer models successfully capture the short-term effects of increasing carbon dioxide in the atmosphere. But the record from Earth's geologic past also encompasses longer-term effects, which accounts for the discrepency in findings. The eventual melting of ice sheets, for example, leads to additional heating because exposed dark surfaces of land or water absorb more heat than ice sheets.
"This analysis shows that on longer time scales our planet may be much more sensitive to greenhouse gases than we thought," Kiehl says.
Climate scientists are currently adding more sophisticated depictions of ice sheets and other factors to computer models. As these improvements come on line, Kiehl believes that the computer models and the paleoclimate record will be in closer agreement, showing that the impacts of carbon dioxide on climate over time will likely be far more substantial than recent research has indicated.
Because carbon dioxide is being pumped into the atmosphere at a rate that has never been experienced, Kiehl could not estimate how long it would take for the planet to fully heat up. However, a rapid warm-up would make it especially difficult for societies and ecosystems to adapt, he says.
If emissions continue on their current trajectory, "the human species and global ecosystems will be placed in a climate state never before experienced in human history," the paper states.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by National Center for Atmospheric Research/University Corporation for Atmospheric Research.

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Journal Reference:

1. Jeffrey Kiehl. Lessons from Earth's Past. Science, 2011; 331 (6014): 158-159 DOI: 10.1126/science.1199380

National Center for Atmospheric Research/University Corporation for Atmospheric Research. "Earth's hot past could be prologue to future climate." ScienceDaily 14 January 2011. 17 January 2011 <http://www.sciencedaily.com­ /releases/2011/01/110113141607.htm>.

Fossil Hunt in Antarctica

Hom

Photo Credit: Patrick O'Connor Paleontologists led by Ross MacPhee look for fossils on Snow Island in the South Shetland Islands off the Antarctic Peninsula. MacPhee is particularly interested in marsupial fossils that could fill out the picture of their dispersal through the Southern Hemisphere.  Reverse course Paleontologists seek evidence that marsupials arose in Antarctica By Peter Rejcek, Antarctic Sun Editor Posted January 14, 2011   Ever see the logo for the Sherwin-Williams Company? It shows a bucket of paint tipped over above the planet. The paint covers the Northern Hemisphere, oozing and dripping south. Ross MacPhee thinks it’s a perfect metaphor for the disrespect the Southern Hemisphere receives from some of his colleagues regarding the evolution and distribution of mammals tens of millions of years ago when Antarctica was part of a larger continent called Gondwana. This austral summer he’ll make a fourth attempt to find mammalian fossils that at least prove some kinds of these land animals were present on the continent long before Antarctica finally separated from other land masses and started to go into a deep freeze 40 million years ago. Before then, Antarctica was sandwiched between South America and Australia, all remnants of the former supercontinent Gondwana. MacPhee is particularly interested in the history of Australian marsupials, believing that their ancestors emerged in South America and traveled across Antarctica to Australia sometime in the neighborhood of 80 million years ago. “It was relatively easy, not only for the small guys like the marsupials, but also bigger ones like some of the southern ungulates [hoofed animals] to get across the land bridge connecting Antarctica and South America and settle down until Antarctic winter came in permanently about 40 million years ago,” MacPhee said during an interview at the American Museum of Natural History, where he is a curator in the mammalogy department. Photo Credit: Patrick O'Connor Fossilized wood found on James Ross Island. The problem is that fossil record from Antarctica is spotty at best, especially considering most of the continent is entombed in ice. “That leaves you with a few little windows of seasonally bare ground on the Antarctic Peninsula and nearby islands,” MacPhee noted. One of the better windows is on Seymour Island off the tip of the Antarctic Peninsula. Almost 30 years ago, U.S. scientists in the journal Science described the first fossil land mammal found in Antarctica, belonging to the extinct marsupial family Polydolopidae. The fossils were recovered from rocks about 45 million years old. The find strengthened the theory that Australian marsupials originated from South American species that dispersed across Antarctica prior to about 65 million years ago, MacPhee said. Marsupials are mammals that are distinguished by the pouches many of them use to carry their young — the most well-known examples being kangaroos. More recently, a study published last summer in the online journal PLoS Biology uses DNA data to suggest that Australian marsupials evolved from a common South American ancestor well before the end of the Cretaceous period 65 million years ago when the dinosaurs famously met their end. Photo Credit: AMNH Ross MacPhee MacPhee, “wildly” but enthusiastically speculating on what he might find during his upcoming expedition, said the possible discovery of marsupial fossils on Seymour or neighboring islands as primitive as those in South America could indicate that the divergence (or origin) of Australian marsupials actually began in Antarctica rather than South America proper. “It would be damn interesting. It implies that Antarctica has been more than a superhighway for species to occasionally traverse,” he said. “It means that during times like the late Cretaceous, when it was much warmer than today, important episodes in mammal evolution might have happened there.” Antarctica of 80 million years ago would hardly resemble the frozen wasteland of today. Some regions would have sported highly diverse vegetation, based on paleobotanical evidence. That means a temperate climate, which favors mammals. “Since there was a great variety of plants, that implies there would have been a commensurately great variety of arthropods and insects, which means there would have been all kinds of available niches for mammals — small mammals, in particular — that eat insects,” MacPhee said.

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Julia Clarke, as associate professor in the Department of Geological Sciences at the University of Texas at Austin, led a team five years ago that reported that close relatives of at least one order of modern birds co-existed with dinosaurs.
The new species, Vegavis iaai, was collected in 1992 by scientists from Argentina on Vega Island off the Antarctic Peninsula. Clarke and her U.S. and Argentine team re-examined the material more than a decade later.
It offered some of the best fossil evidence to date that linked modern bird divergence, the spread of today’s species, before the K-T boundary — when geologic time turned the page from the Cretaceous to the Tertiary period after the mass extinction of the dinosaurs.
MacPhee said such evidence about the Vega waterfowl helps turn the Sherwin-Williams model upside down. “It does suggest the southern end of the world is not as biogeographically irrelevant as it’s been previously — inadvertently perhaps — thought to be.”

Photo Credit: Wikipedia Commons

Map of the South Shetland Islands.

Clarke will join MacPhee and several other paleontologists, including dinosaur fossil experts, on this latest expedition to the islands near the Antarctic Peninsula in February 2011.
“I’m really excited to have the opportunity after looking at all of the Antarctic material to go down there,” Clarke said. “I’ve never been to Antarctica, and I’m very excited to see what we’ll find.”
MacPhee hopes the fourth time is the charm. His first try in 2007 was largely frustrated by heavy snow on the ground that made finding the small fossils he would expect to find nearly impossible. The ancient marsupials would be about the size of modern shrews, up to 100 grams in weight — something that could easily fit in the palm of your hand. [See previous article: Bridge to the past.]
A freak storm in 2008 wrecked the team’s field camp, forcing an early end to their season. Last year, sea ice conditions prevented the research vessel carrying the scientists to access the islands except for two days. [See previous article: A big blow.]
Despite the setbacks, MacPhee is willing to commit another two months to his search for mammalian fossils.

Photo Credit: N. Adam Smith

Julia Clarke

“I feel it’s important. People have to be willing to put up with some pain and suffering if they have any expectations of being successful,” he said philosophically. “Antarctica is not going to be kind. We already know that with regard to how hard it has been to collect mammalian or indeed any vertebrate fossils.”
The team hopes to begin its search on Vega Island, where Clarke’s avian fossils were found.
Other likely expedition sites include nearby Seymour and James Ross islands, where others have found fossils from younger geological periods. In fact, Argentinean scientists recently uncovered ancient turtle fossils on Seymour Island dating from roughly 45 million years ago that don’t belong to any species known to live in the region during that time period.
The scientists expect to spend long hours on their hands and knees, crawling along the ground hoping to spy interesting-looking bits.
“I’m somewhat sanguine, although you have to recognize the realities. That next rock that you needed to kick over to find that tooth that was going to explain all of this might be the very rock that you ignore,” he said.
“For my purposes it’s worth doing, because I think the Antarctic part of mammalian divergence and diversification story in the latter part of the Cretaceous is the part that we know least about. Virtually any evidence would suggest new possibilities.”

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Indian, Australian joint team studying penguin evolution

Sydney, Jan 7 (IANS) A joint team of Indian and Australian scientists is studying molecular changes in Adelie, a penguin species commonly found along the entire Antarctic coast, triggered by global warming.
The experts are also looking at the larger issue of whether climate change drives evolution.

Australian team leader David Lambert is collaborating with Siva Swaminathan, who leads the Indian side, under the aegis of the Australia-India Strategic Research Fund (AISRF).

The AISRF was established in 2006 to facilitate and support science and technology research cooperation between the two countries.

'When global temperatures change (up or down), many animals do not biologically adapt to that change, but simply move to where things are warmer or cooler,' Lambert said.

'With global warming, Adelie penguins are not able to move to a cooler place since they already live in the coldest place on earth. So, they have no option but to adapt,' he said.

In yet another collaborative programme, Arnold Dekker from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) led an Australian team at a recent workshop with Indian researchers to monitor ocean health through remote sensing.

Dekker said researchers use satellite-based observation of earth's coasts and oceans to monitor ocean colour, which arises from changes in algae, suspended and dissolved organic material.

'Ocean colour helps us understand the interactions between aquatic ecosystems, climatic factors and human impacts,' he said.

The experts at the workshop agreed that understanding these interactions can help in forming better policies for protecting coastal reefs and ecosystems from potentially harmful disturbances caused by human activity and environmental stresses.

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Happy New Year!