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January 2020

What Lies Inside the Penguin’s Mouth

The inside of a penguin's mouth

What Lies Inside the Penguin’s Mouth

By Megan Spofford

I recall as African Penguin zookeeper how during feeding times, certain penguins preferred to be fed certain types of fish over others, and most preferred to be fed the head of the fish first (only 1 out of the 40 preferred to be fed tail first). If those penguins were offered an unpreferred item, or in an unpreferred way, the penguin would open its bill and sling its head quickly to the side to shake the fish I had given it from its mouth. In those instances, I had quick glimpses inside the mouth of the penguin, and honestly, it almost looked like something out of a horror story!

What the inside of a penguin’s mouth looks like.

A quick description of a penguin’s bill

From the outside, a penguin’s mouth, the bill, is one of its defining characteristics. There are variations in color for each species of penguin, which can be beautiful, like the King Penguin. The bills are hard keratin formations (keratin is the tissue that makes up human hair, giraffe hooves, and rhino horns). It has a hook on the end that helps a penguin to grip items. (This, of course, comes in handy since penguins do not have arms or hands like us.) There are also two nares on either side of the bill so the penguin can breathe with its bill closed, and which additionally serve as exit points for secretion of the highly concentrated salts they ingest.

What are those spiky things inside a penguin’s mouth?

By shifting focus to the inside of the mouth, we encounter that horror that I mentioned. Of course penguins do not have teeth, but it sure looks like their tongue and the roof of their mouth does! Those teeth-looking structures on the tongue and palate are actually comprised of soft keratin spikes called papillae. They appear sharp on the top, and curve backwards toward the back of the mouth.

What are the functions of those papillae on a penguin’s tongue?

First off, you may notice that those spiky papillae all point toward the back of the penguin’s mouth. Those work a bit like a fish hook. The penguin can grab onto a slippery fish and that food will now only move in one direction – down the penguin’s throat!

All tongues have papillae, including ours, but the penguin’s is more pronounced. It is believed that the reason for this is the function of the tongue. Animals that have “protruding papillae” are typically food collectors. Penguins certainly have pronounced papillae, and collect their food in the ocean! Tongues that have papillae that do not appear to protrude are said to use their tongue as a means to push the food around the mouth, and down the esophagus. Penguins can do this as well, although it has not been well documented. More than likely, the movement is limited, but it can move from side to side, and up and down. Finally, there are tongues that are meant to lie flatly so that food can travel down the esophagus when placed in the correct position. For penguins, all three of these functions seem to apply, with the latter being most applicable to chicks.

Anatomy of a penguin tongue

Underneath the papillae are fatty tissue, connective tissue, mucus glands, and serous glands. The salivary glands are present toward the back of the mouth, and secrete both mucus and serum. In a study conducted on Magellanic Penguin oral structures, salivary glands were present from day 1, but continued to develop, and secrete more beneficial mucus as the subjects got older. Most other birds maintain the same level of development of gland and mucus secretion from birth onward. It was once believed that seabirds who ingested foods from the marine environment would have smaller glands that secreted lesser amounts of mucins because the food was already lubricated by water. However, evidence from the study on Magellanic Penguins supports the theory that the salivary glands have a specific purpose other than to function based on their diet. The purpose could be for any of the following reasons: to break down food, protection from minor injuries, and keeping harmful organisms from creating disease in the mouth. 

What about penguin taste buds?

Most species of birds lack the gene receptors for sweetness, but penguins have even fewer taste buds. Some studies have found that only the receptor genes for salty and sour flavors showed up in penguin species. It’s hypothesized that umami, bitterness, and sweetness gene receptors evolved out of the penguin sequence, because their ancestors lived in cold environments where those receptors do not function well. 

How cool, (horrendous!), and unique is the penguin mouth?!?!

Do you want a mouth, or taste buds, like penguins? Did you like what you learned by reading this blog? Leave a comment below. And please help us to continue to provide you with penguin news articles by donating to Penguins International.

Read more about penguins in some of our other blogs:

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King Penguins

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References:

Hall, Danielle, and Bill Fraser. “Penguins.” Ocean Find Your Blue, Smithsonian, 18 Dec. 2018, ocean.si.edu/ocean-life/seabirds/penguins.

Kobayashi, K, et al. “Fine Structure of the Tongue and Lingual Papillae of the Penguin.” Archives of Histology and Cytology, U.S. National Library of Medicine, Mar. 1998, www.ncbi.nlm.nih.gov/pubmed/9557966.

Paxton, et al. “The Leeds Histology Guide.” The Histology Guide, Faculty of Biological Sciences, University of Leeds, 1 Jan. 1970, www.histology.leeds.ac.uk/oral/tongue.php.

Samar, Maria Elena, et al. “Histochemical Study of Magellanic Penguin (Spheniscus Magellanicus) Minor Salivary Glands during Postnatal Growth.” Wiley Online Library, John Wiley & Sons, Ltd, 19 Nov. 1999, onlinelibrary.wiley.com/doi/pdf/10.1002/%28SICI%291097-0185%2819990201%29254%3A23.0.CO%3B2-7.

Yellow-eyed Penguins – one of the rarest penguins in the world

endangered species, what is the rarest penguins, how many types of penguins are there, where do penguins lives, what do penguins eat, what color eyes do penguins have

The Yellow-eyed Penguin – one of the rarest penguins in the world

by Georgia Podmore

The Yellow-eyed Penguin is one of the rarest penguin species in the world. It is found north of the Antarctic Ocean, along the coast of Southern New Zealand (Ellenberg, Mattern and Seddon, 2009). As the name suggests, the penguin is easily identifiable by the yellow colour around its eyes, along with a brightly coloured yellowish line that runs from its eyes round the back of the head.

Yellow-eyed Penguin characteristics

Like other penguins, the Yellow-eyed Penguin is carnivorous and preys on marine animals, such as crustaceans, cephalopods and fish. They are one of the larger species and can grow to approximately 75cm in height (Ellenberg et al., 2007). The penguins will breed once a year with their mate, who remain faithful to each other. The female will lay two eggs and both parents will help with incubating the eggs until they hatch. Once hatched, the chicks will stay with their parents until approximately twelve months old. The nesting sites for Yellow-eyed Penguins can be found in the forestry and shrubs that run alongside the southeast coast of New Zealand (Doc.govt.nz, 2019). Historically, the nesting sites have been undisturbed, however in recent years the penguins have had to face land predators. This has resulted in the species becoming an endangered animal with a wild population of less than 4,000 individuals (Yellow-eyed Penguin Trust, 2017).

Threats to Yellow-eyed Penguin populations

Predators

Yellow-eyed Penguins must deal with predators near their breeding grounds that are now beginning to hunt on their eggs. These predators include feral cats, stoats, ferrets and dogs (Ellenberg et al., 2007). On land, these predators are generally not a cause for concern for adult penguins. However, due to predation on their eggs, Yellow-eyed Penguin breeding success has been declining in recent years. Predators in the ocean include sharks and fur seals. The penguins have no defense against such large predators in the water, relying strictly on swimming speed and manoeuvrability, or escaping out of the water to dry land. Like all penguins, their colouration also helps disguise them from predators, as sharks and seals may find it difficult to see the penguins from below due to their white chest, or from above due to their black backs.

Human Interference

Humans have already disrupted Yellow-eyed Penguin populations by introducing some of the penguin predators into their areas. Another way in which humans have affected the number of penguins is through disturbance from the tourism trade (Ellenberg, Mattern and Seddon, 2009). Being a spectacular penguin to look at — along with its endangered status — brings in large numbers of people who want to see these animals in the wild before they’re gone. Research has shown that large numbers of tourists can be associated with reduced breeding success, along with decreased fledgling weight, which can then affect their survival rate in the first year (Mattern et al., 2007). These factors may be influenced due to stress on the adult penguins which may affect normal behaviour. 

Disease

As the climate is warming, disease is becoming a bigger issue for Yellow-eyed Penguins. Avian malaria was responsible for 29 deaths in 2018/19 (Yellow-eyed Penguin Trust, 2017), a large and impactful number for such a small population. With increased temperatures leading to increases in mosquito breeding, the threat for disease to penguins is expected to increase. Avian diphtheria is also affecting the species, which is commonly found in young chicks. Bacterial plaque forms in the mouth of the chick and is subsequently inhaled, which eventually causes aspiration pneumonia, a potentially fatal illness.

Stress can also cause penguins to become more susceptible to disease, which for the Yellow-eyed Penguin may be coming from increased threats and tourism. 

Deforestation

Habitat loss has become one of the main reasons the number of Yellow-eyed Penguins are decreasing (Mattern et al., 2007). In New Zealand, forests are being cleared to make way for field areas for grazing animals or homes. This is then resulting in increased pressure for the penguins as they attempt to find nesting areas. 

How can we help these extremely endangered Yellow-eyed Penguins?

Help for the Yellow-eyed Penguin started in the 1980s when the population was extremely low (Sue, 2019). Conservation organisations are focusing on protecting the forest and shrub land for the penguins to ensure they have the space to breed and build their nests, thousands of plants have also been planted around the areas for protection. Although this all sounds beneficial, help is still needed to protect more areas or to re-establish areas that have already been cleared.

In New Zealand, there is the Otapahi Reserve which is a protected area for the penguins, to ensure that they can live and breed without being disturbed by humans and predators. Dunedin Wildlife Hospital has also begun catching penguins with injuries and rehabilitating them. Veterinarian Lisa Argilla states, “We do what we have to do to save the species, as we cannot fix climate change and habitat destruction” (Biologicaldiversity.org, 2014)

There are a large amount of conservation groups and rehabilitation centres now working to support the Yellow-eyed Penguins and to help increase the population. Every effort is being made to ensure that the population is protected, and with support from the public we can all strive to make the maximum impact and hopefully save the Yellow-eyed Penguin from extinction.

Did you know about Yellow-eyed Penguins? And how rare they are? Did you like what you learned by reading this blog? Leave a comment below. And please help us to continue to provide you with penguin news articles by donating to Penguins International.

Read more about penguins in some of other blogs:

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Reference List

Biologicaldiversity.org. (2014). Yellow-eyed penguin. [online] Available at: https://www.biologicaldiversity.org/species/birds/penguins/yellow-eyed_penguin.html [Accessed 31 Aug. 2019].

Center for Biological Diversity (2019). Yellow-eyed Penguin. [image] Available at: https://www.biologicaldiversity.org/species/birds/penguins/yellow-eyed_penguin.html [Accessed 31 Aug. 2019].

Doc.govt.nz. (2019). Yellow-eyed penguin/hoiho. [online] Available at: https://www.doc.govt.nz/nature/native-animals/birds/birds-a-z/penguins/yellow-eyed-penguin-hoiho/ [Accessed 31 Aug. 2019].

Ellenberg, U., Mattern, T. and Seddon, P. (2009). Habituation potential of yellow-eyed penguins depends on sex, character and previous experience with humans. Animal Behaviour, 77(2), pp.289-296.

Ellenberg, U., Setiawan, A., Cree, A., Houston, D. and Seddon, P. (2007). Elevated hormonal stress response and reduced reproductive output in Yellow-eyed penguins exposed to unregulated tourism. General and Comparative Endocrinology, 152(1), pp.54-63.

Mattern, T., Ellenberg, U., Houston, D. and Davis, L. (2007). Consistent foraging routes and benthic foraging behaviour in yellow-eyed penguins. Marine Ecology Progress Series, 343, pp.295-306.

Sue, M. (2019). Penguins: Yellow-eyed Penguins – Megadyptes antipodes. [online] Penguins.cl. Available at: http://www.penguins.cl/yellow-penguins.htm [Accessed 31 Aug. 2019].

Yellow-eyed Penguin Trust. (2017). Distribution and habitat. [online] Available at: https://www.yellow-eyedpenguin.org.nz/penguins/distribution-and-habitat/ [Accessed 31 Aug. 2019].

Penguins are overheating! Yep, you read that right!

Penguin skin showing feather density

Penguins are overheating! Yep, you read that right!

By Beth Storey-Jones

What do you imagine when you think of penguins? 

  • Highly adapted?
  • Caring parents? 
  • Amazing swimmers? 
  • Looking fly in their tuxedos? (no pun intended)

Well you would be 100% correct on all accounts. You might also worry about how they may struggle to keep warm? In fact, this isn’t their primary issue. They’re actually more at risk of overheating! Yes, I did say overheating. This is a real problem and is becoming detrimental to penguin populations. Let me explain!

Brief penguin anatomy and physiology lesson

First, let’s take a brief look at a penguin’s anatomy and physiology. They are aquatic, built for life at sea. To allow them to thrive in the water, warm-blooded animals need to be well insulated. Whales have blubber, seals have thick fur pelts, but birds have neither. Evolutionarily speaking, birds avoided adaptations that would hinder flight. So, penguins have had to use pre-existing characteristics and tweak them to survive in their niche, this being their feathers.  As a result, these feathers are short, ridged and interlock [1] to form an air trap (figure 1). Which is equivalent to a dry suit. Any heat obtained by the bird is kept in between the base layer of the feathers and the top layer of the skin, and works well as an insulator when in the water. The trouble comes when this same heat is not released, as when they return to land.

Fig. 1 Penguin skin showing feather density [1]

Penguin Distribution – Where do they live?

Fig. 2 Penguin Range Map [2]

Contrary to popular belief, most penguin species live in temperate and even tropical zones, not Antarctica (Fig. 2). Consider the Little Blue Penguin, who breeds up and down the coasts of Australia and New Zealand [2]. They often only come ashore once the sun begins to set. A more popular species, the Galapagos Penguin, avoids direct sunlight by creating nesting areas in shaded lava rock cracks. Water temperature can also be as high as 30oC (86.0°F) around the equator [3] and for a bird that has to maintain an internal body temperate of 39oC (102.2°F) this can be challenging. With their feathery armour only just able to regulate this temperature, prevention methods aren’t always the best medicine.

So, how do penguins combat hyperthermia? To answer this question in short, thermoregulation adaptations. It’s really interesting, so I’ll elaborate! You may have noticed that quite a few bird species have naked legs or webbed feet, or both. These areas of the body house complex blood vessels which can constrict to control the amount of heat loss when cold or expand to lose heat when the animal is too hot, comparable to a radiator [3]. Penguins such as the Humboldt Penguin also have featherless faces. Behaviourally, penguins pant. Which evaporates the body’s moisture while using up body heat to do so. Much like your dog, when he’s retrieved his favourite tennis ball for the 100th time. Penguins will also hold their flippers out to the side to allow breezes to cool them down even further.

Chicks at risk

Penguin chicks are also at risk of overheating. Their soft down is even more efficient at heat retention. While unable to thermoregulate, chicks are sheltered from the sun by their parents. Unlike the adults, their flippers are also covered in insulating down. So, the babies have to rely on their disproportionately large (and cute) feet (Fig. 3) to act as a personal radiator [3]. On exceptionally hot days, juveniles have been observed essentially laying like a starfish on the ground to expose their feet. Some species will even stand in water. 

Fig. 3 The extra-large feet of a penguin chick [3]

Challenges ahead…

So far, it has been explained that heat regulation is a bit of a challenge for the penguin. That is without even taking into consideration our global warming crisis. I know, I know, everyone is talking about it. But it is a vital element to consider in the lives of our beloved penguin friends. The finely tuned adaptations we have talked about did not happen overnight. It was through the millenia-long trial and error process of evolution and will still be ongoing today. These adaptation changes aren’t necessarily a problem, but it’s the small window of opportunity that these animals (as well as other species) have to do it in when temperatures rise quicker than evolution. Sadly, this is where the detrimental part comes in. Sea temperatures are increasing. Penguin chicks are struggling to survive due to poor food quality and quantity from these temperature increases[4]. The warmer climes seen in Antarctica recently are causing unprecedented rainfall and the melting of potential snowfall. This can be damaging to eggs that must be kept dry and warm. And the chicks may also become muddy and wet and can succumb to hypothermia because their down feathers are not waterproof[4].

Let’s bring it all together. Penguins live in water. They inhabit not only the harsh, dry and cold parts of the world, but surprisingly also some of the hottest. They have finely-tuned mechanisms to allow them to do so. Such as radiators for feet and dense plumage for when they need to stay warm. But these adaptations are so specialised to their surroundings, that any changes can be fatal. With sea temperatures rising, food availability and competition is high, as well as the risks of chicks being exposed to hyper or hypothermia. This brings a bit of a chilly end to an extremely cool topic!

Thinking of penguins in general, do you think they would overheat? Did you like what you learned by reading this blog? Leave a comment below. And please help us to continue to provide you with penguin news articles by donating to Penguins International.

Read more about penguins in some of other blogs:

Like our penguin blogs? Sign up for our newsletter to get them right in your inbox!

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Reference List

  1. DeNapoli, D. 2010. The Great Penguin Rescue. New York. Free Press. 
  2. Muller-Schwarze, D. 1984. The Behaviour of Penguins – Adapted to Ice and Tropics. New York. State University of New York Press
  3. Kaiser, G. 2007. The Inner Bird: Anatomy and Evolution. Vancouver. University of British Columbia. 
  4. Sidder, A. 2016. Antarctica Could Lose Most of Its Penguins to Climate Change. [online]. National Geographic. Available from: https://www.nationalgeographic.com/news/2016/06/adelie-penguins-antarctica-climate-change-population-decline-refugia/ [Accessed 24 October 2019].

Figures

  1. National History Museum. 2018. Ever wondered how Emperor Penguins survive temperatures of -60 degrees centigrade? Their feathers are densely packed as these photos show but as researcher Cassondra L. Williams and colleagues discovered there is more to the story than meets the eye. [online]. Twitter. Available from: https://twitter.com/nhm_oology/status/1022076201828012032 [Accessed 24 October 2019].
  2. Kikkawa, E., Tsuda, T., Sumiyama, D., Naruse, T., Fukuda, M., Kurita, M., Wilson, R., LeMaho, Y., Miller, G., Tsuda, M., Murata, K., Kulski, J., & Inoko, H. 2009. Trans-species polymorphism of the Mhc class II DRB-like gene in banded penguins (genus Spheniscus). Immunogenetics. 61, 341-352.
  3. Tennessee Aquarium. 2017. Call It “Sasquawk”: Big Feet a Distinct Feature of the Aquarium’s Newest Penguin Chick. [online]. Tennessee Aquarium. Available from: https://www.tnaqua.org/newsroom/entry/call-it-sasquawk-big-feet-a-distinct-feature-of-the-aquariums-newest-pengui [Accessed 24 October 2019].

Have Penguins Ever Been Able To Fly?

Humboldt Penguin showing off its flippers and swimming ability.
(© Martin Franklin/ZSL)
Humboldt Penguin showing off its flippers and swimming ability.

Have Penguins Ever Been Able To Fly?

by Martin Franklin

Swimming is normal for me. I’m relaxed. I’m comfortable, and I know my surroundings. It’s my home.” (Michael Phelps, most decorated Olympian of all time).

Swimming is a confusing sport. Sometimes you do it for fun, but then other times you do it to not die. And when I’m swimming, sometimes I’m not sure which one it is. You have to go by the outfit. Pants – oh oh! Bathing suit – ok! Naked – we’ll see!” (Demetri Martin, comedian).

Penguin conservation is imperative!

(© Martin Franklin/ZSL)
Humboldt Penguins with a view of their flippers in the water.

In the course of my work as a zookeeper at ZSL London Zoo (a charity which supports animal conservation projects all over the world), I frequently get asked some pretty odd (often brilliant) questions. Recently two 6- or 7-year-olds asked me, “Have penguins ever been able to fly?” (A great question, I thought). Although we ended up talking about traits these children had inherited from their grandparents, I ultimately utterly failed to explain in simple enough terms to them how evolution works – entirely mea culpa. (Incidentally, for thoroughly clear and persuasive introductions to the facts and mechanisms of evolution, I’d highly recommend reading both Coyne1 and Dawkins2).

This incident did, however, prompt me to write this piece. Of course, penguins, as we understand and envisage them, have never been able to fly. But their ancestors, from whom they evolved, unquestionably could. The real question is to ask what pressures or opportunities caused that change.

Why do penguins swim instead of fly?

First, however, a quick look at flightlessness in birds generally. Although flying has proved advantageous to most bird species (and has thus been retained), a wide range (in terms of size, geographical spread and ecology) have evolved to discard the power of flight once possessed by their ancestors. These include:

  • “Ratites” (i.e. ostriches, rheas, emus, cassowaries and kiwis, plus the now extinct moas and elephant birds), which lack a keel (ridge) on their sterna (breastbones) onto which to attach flight muscles. 
  • Numerous waterfowl (Anseriformes) (e.g. Aukland Teals and Campbell Teals).
  • Two species of grebe (Podicipediformes) (i.e. Junin Grebes and Titicaca Grebes).
  • One of the pelican/cormorant group (Pelecaniformes) (i.e. flightless cormorants). 
  • One of the parrot group (Psittaciformes) (i.e. Kakapos). 
  • Numerous rails (Gruiformes) (e.g. Calayan Rails and Pink-legged Rails).
  • A variety of now extinct birds, including from the: pigeon and doves (Columbiformes) (e.g. Dodos); gamebirds (Galliformes); hoopoes (Coraciiformes); birds of prey (Falconiformes); owls (Strigiformes); nightjars (Caprimulgiformes); perching birds (Passeriformes); and auks (Charadriiformes).

Many of these flightless species come/came from remote, predator-free, food-abundant islands, which helps explain why they lost the ability to fly. It is “expensive” (in terms of energy required and lost other opportunities) for birds to maintain the necessary physical attributes needed for flight (e.g. large, calcium-rich, keeled breastbones and large chest muscles). Therefore, if it’s no longer necessary to fly to avoid predation or hunt, natural selection frequently results in less investment in such “expensive” materials/attributes.3

Flightlessness exists in many birds besides penguins

Flightlessness has also evolved independently in:

  • large-bodied, herbivorous birds (e.g. ostriches, emus, cassowaries, moas and elephant birds), as a diet of high-volume low-quality vegetation favours developing a large body, which in turn increases the challenges of maintaining the apparatus needed for flight; 
  • several foot-propelled diving birds (e.g. flightless cormorants), as these evolved to have powerful, paddle-like legs and feet (so their wings and chest-muscles became increasing less important for locomotion, and accordingly regressed); and
  • penguins (i.e. wing-propelled divers, that in water use their feet as a rudder, rather than for propulsion). These are by far the largest bird family whose entire members are flightless.4

The transition from flying birds to wing-propelled divers was a gradual process which started around 65 million years ago for penguins, and would have involved an intermediate stage whereby its ancestors could use their wings for both flying in the air and diving/swimming underwater (much as Razorbills, for example, do today). These ancestors were probably seabirds similar to modern diving petrels.

Strategies for a bird to choose swimming vs. flying

One of two strategies can be adopted once such a bird reaches a critical size of around 1kg (above which the size of wing needed for flying becomes too large for efficient swimming). Either: 

(1) the wings can be kept solely for flying, and the feet/legs can be used for underwater propulsion (as observed in most modern ducks and cormorants); or 

(2) aerial flight can be abandoned in return for superior underwater swimming (as happened with penguins).4,5

Gradually, therefore, as this ancestor fared better swimming underwater than flying above it:

  • No longer constrained by the necessity of flying as well as swimming, it was able to increase its weight. (One now-extinct penguin species, Anthropornis nordenskjoeldi, weighed around 135kg, and the modern Emperor and King Penguins are also relatively large animals). 
  • Slim wing bones became increasingly shorter and heavier, eventually resulting in the flat, broad (and less flexible) flippers sported by modern penguins.
  • Other related adaptations developed, including, for example, a hydrodynamic body shape and denser bones (unlike flying birds’ air-filled bones), meaning penguins are not overly buoyant. 

As a result, by 55 million years ago, penguins were completely flightless but thoroughly adapted to life in water.4,5

(© Martin Franklin/ZSL)
Streamlined bodies and rigid, flat flippers allowing strong swimming ability in penguins.

The adaptations that penguins have developed over thousands of years never ceases to be fascinating. Tell us your thoughts in the comment sections below. And please consider assisting with our conservation projects and helping us to continue to provide you this information by donating to Penguins International.

Read more about penguins in some of other blogs:

Like our penguin blogs? Sign up for our newsletter to get them right in your inbox!

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References

1 Coyne, J. A. (2009). Why Evolution is True. Oxford University Press: Oxford.

2 Dawkins, R. (2009). The Greatest Show on Earth. Transworld Publishers: London.

3 McNab, B. K. (1994). Energy Conservation and the Evolution of Flightlessness in Birds. The American Naturalist. Vol. 144, no.4, 628-642.

4 Gill, F. B. and Prum, R. O. (2019). Ornithology. (4th edition). W. H. Freeman and Company: New York.

5 Lynch, W. (2007). Penguins of the World. A&C Black Publishers Limited: London.

Black and White, the Perfect Combination

Black and White, the Perfect Combination

Black and White, the Perfect Combination

By Megan Spofford

Dressed to the nines – penguin countershading

Penguins are often referred to as “wearing tuxedos”; an anthropomorphism that describes how most penguins have black feathers on their back with white on their belly. 

The tuxedo look of the penguin is known as countershading in the zoological field. Countershading describes how an animal is darker on the part of their body that faces the sun, and is lighter on the part that faces away from it (an example of this can be seen in the image above). It is important to remember that countershading only describes the coloration pattern of an animal, and not to use the term to define what it does for the animal.

Countershading provides penguin camouflage

The evolutionary purpose of countershading is highly debated, but it is most widely believed to function as a type of crypsis when a penguin is in the water. Crypsis is defined as a type of camouflage that protects an animal from predation. There are arguments for which category of crypsis it may fall under: either self-shadow concealment, or background matching. Self-shadow concealment essentially makes the penguin appear as a flat image, and potentially harder to distinguish from other things typically found in the environment, like rocks or ice. Background matching is where the penguin gets lost in its surroundings, because they look identical.

Penguin coloration under the water

It might stretch your imagination to think of a penguin being camouflaged in open water, however, marine habitats are the best at providing optimal lighting for a countershaded animal to blend in. When an animal is in the water, the light source is always directly overhead, making lighter colored objects closer to the surface harder to distinguish. When looking downwards, the ocean continually darkens, so dark objects would be obscured in this area. Because many natural penguin predators are strictly marine animals, it would make sense that they evolved feather colors that would make it harder for those predators to see them no matter where they happen to be located in the water. It is also beneficial for the penguin to be countershaded so that they themselves can prey upon fish and crustaceans!

 

Fossil evidence for the countershading hypothesis

The idea of countershading for camouflage has intrigued zoologists, artists, and militarists (who utilized the concept for weapons and bomber planes) for years. There are some proponents, however that believe the color of penguin feathers may be attributed to other factors, and the evidence for this is based heavily on the findings of a fossil from an extinct penguin in Peru.

Scientists were able to determine the color of feathers of the giant, extinct penguin despite degradation. They did this by examining melanosomes in the feather under a microscope, and it showed that they were a reddish color, instead of black.

Melanosomes are the organelles which create, store, and move melanin pigments in animal tissue. Melanin can come in one of two forms: eumelanin which has an oblong shape and accounts for darker pigmentation, and pheomelanin which is shorter and rounder (like an oval) and accounts for lighter pigmentation. In a comparison of feather color based on melanin, the fossil showed that it was colored by pheomelanin, while existing penguins are colored by eumelanin. 

What does melanin do, and what could that have to do with the color pattern of extant penguins?

There are a few different reasons eumelanin might have been triggered to be produced. In order to determine why this occurred in modern day penguins, we have to take a look at the environmental conditions that foster its development.

One that most of us are familiar with is its protective properties from harmful UV radiation. When skin, or feather tissue, is exposed to high levels of UV radiation, eumelanin is produced to block those rays, and thus becomes darker. For penguins that spend time at the equator where UV exposure occurs the most, they would need this melanin protection to keep from developing cancers. Obviously, the ventral (belly) side of a penguin is not exposed to UV radiation while swimming, which is why it would be lighter than the dorsal (back) side that is exposed.

Eumelanin has a molecular structure that is resistant to injury and breakage. Having eumalenain in the majority of your feathers would be beneficial for an animal that moves around on jagged ice formations, or has a high amount of drag load placed on their feathers while swimming speedily, like a penguin.

Further benefits of darker melanin are that it limits blinding glare (when light reflects off of a surface and affects vision), and it helps an animal camouflage into its surroundings in certain types of light (as discussed above!)

So, was eumelanin in feathers adapted mainly for camouflage purposes, or did it become a staple of modern day penguin genetic make-up for one of the other reasons, and it just so happens to also aid in crypsis? Researchers continue to test hypotheses to solve the mystery about the function of the countershaded penguin, so maybe one day soon we will have a definitive answer!

A blend of tuxedo and camo. Penguins are amazing animals. Like this story? Have a story of your own? Leave a comment below. And please help us to continue to provide you with penguin news articles by donating to Penguins International.

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References

Britannica, The Editors of Encyclopaedia. “Melanin.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/melanin.

Clarke, Julia A., et al. “Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers.” Science, American Association for the Advancement of Science, 12 Nov. 2010, https://science.sciencemag.org/content/330/6006/954.full.

Rowland, Hannah M. “From Abbott Thayer to the Present Day: What Have We Learned about the Function of Countershading?” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, The Royal Society, 27 Feb. 2009, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2674085/.

Stevens, Martin. “Animal Camouflage.” Google Books, Cambridge University Press, 7 July 2011, https://books.google.com/books?id=10TCvK-9v70C&pg=PA9&lpg=PA9&dq=ssc+camouflage&source=bl&ots=Kwy7skUjOm&sig=ACfU3U0X7ZZMAjFslKA_aAT05Z1-S3IgGA&hl=en&ppis=_c&sa=X&ved=2ahUKEwjzteO38K7lAhVOnJ4KHYYNCeMQ6AEwD3oECAkQAQ#v=onepage&q=ssc camouflage&f=false.

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