Posts Tagged ‘Modern penguins’
Today a neat new study was published demonstrating that it is possible to determine what a penguin was eating from its bones. The article appeared in Journal of Avian Biology, and was written by two of my favorite penguin collaborators, Dr. Daniel Thomas and Dr. Ewan Fordyce (recent winner of the Hutton Medal) and their colleague Keith Gordon. They applied a method called Raman spectroscopy to measure the chemical composition of penguin bones from museums in New Zealand. Raman is a cool technique. Basically, they blast the bones with a low-powered laser, and the way energy is scattered back gives a good estimate of what elements are prevalent in the bone. Raman spectroscopy is really useful because it does not damage the bone. Other methods for determining chemical composition usually require a bit of bone to be vaporized, which many museums don’t want to see happen.
So what does this have to do with penguin diet? Well, there is an old saying: You are what you eat! It is true at the finest scales. Different species of penguins like to eat fish, squid, or krill. These prey have different concentrations of elements in their bodies due to the different ways the metabolize food and pull oxygen from the water. Krill are very rich in the element fluoride, which they tend to concentrate in their hard carapace. You may be familiar with fluoride as a key ingredient in toothpaste! It is actually toxic, which is why it helps fight the bacteria that cause cavities. However, it is not dangerous at very low concentrations. Our toothpaste has only a tiny, tiny fraction of fluoride, enough to zap a microbe but not enough to hurt us. Fluoride in toothpaste also alters the mineralogy of our tooth enamel, making it harder and less susceptible to dissolving when contacted by acids (like those in soda). Penguins digest their prey in such a way that most of the fluoride stays in the bones or carapaces and gets passed away harmlessly. They do keep some though – think of it like shrimp flavored toothpaste for animals without teeth.
In the new study, the Raman data showed a big difference in the bones of krill-loving penguins compared to fish-loving penguins. Two species that eat large quantities of krill, the Emperor Penguin and the Adélie Penguin, showed higher spectra bands than the other four species included in the study (Humboldt, Little Blue, Yellow-eyed, and Fiordland Penguins), which eat almost no krill. This proves the method works, and it give penguin scientists a new tool to look at how feeding patterns have changed in penguins over time. Actually, there are other ways to reveal diet from long-passed penguins too, including isotopes in eggs and guano (penguin poop).
With all these techniques, it is possible to look at old museum specimens from one hundred years ago or more to see if the diet of penguins has changed along with the growth of fisheries or changes in climate. Indeed, some of this work is already going on. We will return to the topic later.
Reference: Thomas, D.T., R.E. Fordyce and K.C. Gordon. In Press 2013. Evidence for a krill-rich diet from non-destructive analyses of penguin bone. Journal of Avian Biology 44.
This week I am working on some fossil penguin bones from South Africa, and was reminded of the antics of Black-footed Penguins I have seen in zoos. Like most penguin species, they are surprisingly good jumpers, and this ability is subject to active research by marine biologists.If you have ever watched penguins swimming at eye level through glass walls at an aquarium, you may have noticed bubbles streaming from their feathers. It’s great fun to observe these birds zipping past like living Alka-Seltzer tablets. However, there is a point behind the bubbles, and a new study shows that releasing air at the right time helps penguins launch themselves out of the water.
Air has lower viscosity than water, so adding a layer of air around an object can help it cut through the sea more efficiently. Engineers have even applied this concept to make speedier torpedoes. Scientists studying film of diving penguins found that Emperor Penguins store air in their plumage, which gets compressed as they dive. Moving from deep water to shallow water lowers the pressure on the air, just like when one takes the cap off a bottle of soda. As the penguins near the surface, they are able to shift their feathers so as to release the air, which escapes in bubble form. This creates a smooth layer over much of the penguins plumage, which cuts down on friction and drag, allowing the penguin to build up a serious speed. An Emperor Penguin can reach velocities of up to 3 meters per second as it jumps out of the sea onto land. This may seem like fun and games, but when a bird needs to emerge from a hole in a thick sheet of ice or make it up a steep cliff, high speeds are critical. Check out some leaping penguins in action:
You can also read the original scientific article for free here.
Reference:Davenport, J., R.N. Hughes, M. Shorten and P. S. Larsen. 2011. Drag reduction by air release promotes fast ascent in jumping emperor penguins—a novel hypothesis. Marine Ecology Progress Series 430: 171-182.
David Stephens at National Geographic snapped this picture of a rare white penguin on the Aitcho Islands. This Chinstrap Penguin (Pygoscelis antarcticus) is not albino, it is leucistic. Albino animals lack pigment, typically because of a flaw in an enzyme involved in producing melanin. You may remember learning a little about penguin melanin in the fossil penguin Inkayacu. Leucistic animals are able to form melanin, but generally have a mix of cells that produce melanin and cells that cannot. This results in a “washed out” appearance in cases like the penguin below. Whatever triggered the condition (typically a gene mutation is involved), the penguin ended up with light brownish coloration on its back instead of the black coloration of normal Chinstrap Penguins. Notice, though, that the beak and part of the feet are still black. Leucism often affects a particular area of a bird rather than the entire individual. White penguins turn up in the wild every year. However, it appears that either the mutations associated with leucism are recessive or the condition harms the penguins by ruining their counter-shading camouflage, because second generations have never been documented.
It is penguin raising season again at the Central Park Zoo. One of the really neat things about the zoo is that they keep their penguins on Southern Hemisphere time. As the austral calender rolls on, the penguins go through their yearly cycle of molting, pairing, and nesting. This adds extra value to your zoo membership, as you can visit on different weeks and see penguins diving for pebbles, tending to eggs or standing around grouchily while their molted feathers clog the filters. As winter approaches in New York and the days get shorter, the penguins get a full Antarctic summer day’s worth of light and start working on their nests. Each year, several batches of eggs hatch at the zoo, yielding a new crop of baby Chinstrap (Pygoscelis antarctica) and Gentoo (Pygoscelis papua) penguins. This year, there is a special blog covering it all: http://chicks.centralparkzoo.com/
I just found out about this set of land and underwater webcams trained on the Blackfooted penguins in the California Academy of Sciences. Check them out if you need a live penguin fix now that Happy Feet has left his enclosure in New Zealand.
Happy Feet, the Emperor Penguin who got lost and ended up in New Zealand, has been released back into the ocean. People the world over are hoping he will make his way back to his natural home in Antarctica. You can track his progress (monitored by a satellite transmitor attached to his tail) at: www.nzemperor.com
A while back, we talked about the shape of the evolutionary tree of penguins. There are lots of dead branches, lineages that separated from the main trunk and evolved in their own direction for millions of years, and then died off. Most of my own interest lies in these ancient branches. But the green part of the penguin tree is important too, and the branching pattern is far from settled. Scientists are interested in knowing how living penguins are related to one another for many reasons, including understanding the timing of the penguin evolutionary radiation, determining which environment was preferred by the earliest “modern” penguins, figuring out how many times shifts in body size occurred, and more.
Today, we have the opportunity to meet 19 species of living penguins if we are willing to travel far and wide. These are divided up into six genera. Scientists classify groups of closely related species into genera, and together the genus and species name make up the formal binomial name of a species. Thus, the Humboldt Penguin, a member of the genus Spheniscus, is officially known as Spheniscus humboldti. Some penguin genera have only a single species, and others have many.
Let’s take a quick tour of the extant penguin genera. Spheniscus is the genus for “tuxedo penguins”. Although all penguins look at least a bit like they are wearing tuxedos, Spheniscus penguins look finest of all because they have a black band of chest feathers that gives the appearance of a bow tie. There are four living species, the South American Humboldt and Magellanic Penguins (Spheniscus humboldti and Spheniscus magellanicus), the African Blackfooted or Jackass Penguin (Spheniscus demersus) and the Galapagos Penguin (Spheniscus mendiculus). These penguins are all fish-eating specialists, and have strong jaw closing muscles and sharply hooked beaks. In the details of their skeleton, they are more similar to primitive extinct penguins than are any of the other living species. Spheniscus penguins inhabit some of the hottest environments that penguins survive in today, including coastal desert areas of South America and island directly on the Equator.
Eudyptula has only a single species, the Little Blue Penguin (Eudyptula minor). The Little Blue is by far the cutest of the penguin species (if you don’t believe me, see it being tickled here). Little Blues received their common name from the fact that they are the smallest living penguins (standing a little over one foot high) and have a unique blue plumage.
Megadyptes also has only one species, the Yellow-eyed Penguin (Megadyptes antipodes). Arguably the most visually striking species, Yellow-eyed Penguins are characterized by their eponymous bright yellow iris as well as a band of yellow feathers that spread like a bandit mask across their faces. Yellow-eyed Penguins are one of the rarest species, with a only few thousand breeding pairs in the New Zealand region.
Eudyptes includes the eight species of Crested Penguins, which are perhaps the most noodley-looking penguins. These species all have bright yellow head plumes, which give them a rakish or foppish appearance depending on the angle, posture and dryness of the bird’s head. A popular aquarium species is the Macaroni Penguin (E. chrysolophus), so named for their fancy plumage’s resemblance to the 1700s Macaroni wig fashion. Depending on whom you ask, there are between one and three species of Rockhopper Penguin (I feel the DNA and plumage evidence for three separate species is strong). The three candidates are the Eastern Rockhopper (E. filholi), Northern Rockhopper (E. moseleyi) and Southern Rochopper (E. chrysocome). Two of the rarer species are the thick-billed Fiordland Penguin (E. pachyrhychus), a denizen of New Zealand, and the Snares Penguin (E. robustus) which breeds only on (you guessed it) Snares Island. Rounding out the bunch are the Royal Penguin (E. schlegeli) which breeds far to the south in the Sub-Antarctic and the Erect-crested Penguin (E. sclateri), an endangered species that lives on several small Pacific islands. You’re unlikely to see either of these in aquaria.
Pygoscelis is the genus that includes the stiff-tailed penguins (the Latin genus name refers to this trait). There are three species, all of which favor cold environements. The popular Adélie Penguin (Pygoscelis adelie) is one of the World’s most common penguins, with an estimate global population of around 5 million individuals. The Gentoo Penguin (Pygoscelis papua) is a rather husky penguin with a bright carrot-colored bill. The Chinstrap Penguin (Pygoscelis antarctica) gets its common name from the thin black band of feathers under its chin that make it look like it is wearing a tiny helmet.
Finally, the largest and most popular penguins belong to the genus Aptenodytes. Emperor Penguins (Aptenodytes forsteri) and King Penguins (Aptenodytes patagonicus) are tall, graceful birds with long, thin bills and striking orange color patches on their necks and lower bills. These species are unique in that they lay only one egg. They are also unique in holding their chicks on top of their feet while brooding. Given the incredibly harsh conditions they nest in, it would be impossible to raise two chicks this way.
Scientists have attempted to unravel the evolutionary relationships of the living penguin species using both their morphology (the shapes, colors, and arrangements of their bones, feathers, and muscles) and DNA evidence. Both lines of evidence suggest that Spheniscus and Eudyptula form one closely related group, and that Megadyptes and Eudyptes form another. However, they disagree on which group of penguins is the most basal – that is which split off from the main trunk of the penguin tree earliest. DNA evidence suggests that Aptenodytes was the first group to branch off, while skeletal evidence suggests that the Spheniscus+Eudyptula group was first. The diagram above shows where the two sources of data agree, with arrows indicating the alternate hypotheses of which branch is nearest the root of the tree. While it might seem like an academic debate, the implications are huge. If Aptenodytes is the most basal lineage, it would provide evidence that the common ancestor of living penguins was relatively large and that Spheniscus penguins reverted to a primitive skull configuration late in their evolutionary history. But if Spheniscus is most basal, the skulls of modern penguins have probably changed in a major way only once, and a surprising South American origin for penguins becomes quite plausible. Because the two types of data (DNA and morphology) offer conflicting evidence, sequencing more genes and searching for more fossils from near-modern penguins will be important tasks for future studies.