Friday, May 25, 2012

Dallas Zoo

Today we went to the zoo to study bird anatomy and penguins.

Penguin shape
The shape of a penguin body is perfectly adapted to a life in the sea. As Kevin Shafer appropriately writes in his book Penguin Planet: "Fat in the middle and tapered at both ends". With this streamlined shape a penguin experiences the least possible resistance while swimming in the ocean.
Penguin coloration / Countershading
Penguin countershading: a black back and white stomach is a form of camouflage.
All penguins have black backs and white bellies. This type of coloration is called countershading and is a form of camouflage. When seen from above, the penguin would be hard to distinct from the dark ocean bottom. When viewed from underneath, the white stomach would blend in with the skylight.
In addition to these countershaded colors (common to all species), different species have specific colors for some body parts.
Penguin ears

When looking at a penguin, you will not be able to see its ears. That's because they have no external ears like humans do. Penguins hear through two small holes that are located at about the same place as a human's ears. The holes are covered with feathers.

The ability to hear is very important for penguins. Penguin calls are distinctive. By listening to the call a penguin can find its partner throughout a colony of several hundred other penguins that all look alike. Penguin vocalizations are also important in penguin communication: courtship, fights, ...
A penguin bill is used to catch food, to preen penguin feathers and as a weapon in penguin fights. Species that mainly eat fish have longer, thinner bills than species that mainly eat krill (these species have shorter, thicker bills)

Penguin bill (or penguin beak)

Like all birds a penguin has a bill or beak. It is mainly used to catch food, but is also used to preen penguin feathers and as a weapon in penguin fights. Size and sharpness of the bill vary with species. Species that mainly eat fish have longer, thinner bills (like King and Emperor penguins), while species that mainly eat krill have shorter, thicker bills (for example Rockhopper and Macaroni penguins).
Penguins do not have teeth. Inside the bill there are spiky spines pointed towards the throat that help in swallowing living food. Penguins do have tongues, however these are not often seen since they are short.
Penguin legs and penguin feet
Penguin legs are set all the way to the back of their body. This causes an upright stand. Other birds have their legs placed in the middle of their body, causing a horizontal stand.
Penguin legs are set all the way back compared
to that of other birds,
causing an upright stand.
Penguins have very short legs, which are used under water for steering. On land it's not easy for a penguin to walk. Waddling seems to be the easiest way to walk with short legs (in fact this has been researched by scientists). In addition, some species displace themselves by hopping over the ground.
Although you don't see them, penguins do have knees and upper legs. They are completely enclosed within the penguin body. The upper leg is oriented horizontally. In contrast to other birds (whose feet are placed in the middle of their body) penguin feet are set all the way back, causing an upright stand.
Penguins have webbed feet like other swimming birds. They are used for steering under water, but also as while toboganning, waddling and hopping.
Penguins have webbed feet (Humboldt)
All penguins have webbed feet, an adaptation to their aquatic lifestyle in the sea. They also have sharp claws that are not retractable.
Penguin feet (together with the flippers) are used when tobogganing over the ice. This is a method Adelies and Emperors often use to get somewhere quickly and consists of gliding over the ice on the penguin belly.
Sometimes Emperor or King penguins that are standing still, rest only on their heels. They point their feet in the air, minimizing contact with the cold ice. This way these penguins release less body heat.
Penguin tail
A penguin tail is short and in the shape of a wedge. There are 14 to 18 stiff tail feathers. Adelie, Chinstrap and Gentoo penguins have longer tails than the other species, and these are sometimes used as a prop on land or when climbing a steep hill.

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