There are many answers to this question but one of the most intriguing was formulated when paleontologists discovered the complete skeleton, including feathers, of an extinct penguin dubbed Inkayacu paracasensis, the "Water King."
When the Water King's skeleton was found on the Pacific coast of Peru in 2008, scientists had just recently discovered they could determine the color of fossil animals by examining the size and shape of cellular structures called melanosomes. Armed with this information they figured out that Inkayacu paracasensis was gray above and reddish-brown below.
On a skeletal basis he looked just like a penguin though at five feet long he was larger than any alive today. By comparison the largest living penguin, the Emperor Penguin, is about four feet long.
But the Water King probably couldn't swim as well as today's penguins. Scientists theorized that this was because he wasn't black.
Black pigment, called melanin, provides strength to the structures it colors. For penguins the structures requiring the most strength are their wings because they use them to literally fly through water. Water is 800 times denser than air so flying underwater is a very strenuous activity.
The Water King was gray, today's penguins are black. Are modern penguins black because melanin gave them stronger wings? Maybe.
And why are penguins half white? Perhaps because they're better camouflaged underwater when their bellies are white.
When I was a kid I would try to fly by holding my jacket open on windy days. This didn't work because I was too heavy and my "wings" were too short for the wind to lift me.
Weight is clearly a disadvantage if you want to fly. The more you weigh the bigger your wings have to be and, as we learned in 2009, there is a limit to how big you can be and still replace your flight feathers in a reasonable amount of time.
To adapt for flight, birds lightened their skeletons by evolving hollow bones. This sounds fragile but the bones are strong because they are braced internally by tiny trusses. You can see these trusses as a network inside the outer edge of the bone pictured above or click here to see a drawing that shows how engineers borrowed this structure to strengthen bridges.
Not all birds have hollows bones. Loons, for example, dive deep underwater for their food. For them buoyancy (air inside hollow bones) would be a disadvantage, so their bones are solid.
If you don't read PABIRDS (an email list of nearly 1,000 birders in Pennsylvania), you probably missed today's report by Ryan Ford, a member of the University of Pittsburgh's Birding and Ornithological Club.
Subject: Pitt Campus Merlin
From: Ryan Ford <RMF42 AT PITT.EDU>
Date: Tue, 7 Dec 2010 16:05:38 -0500
As I was walking to my afternoon class I heard several chickadees giving
alert calls between the Cathedral of Learning and Schenley Plaza on the
University of Pittsburgh campus.
An adult MERLIN then shot past just 10ft above my head with one of the
local Peregrine Falcons chasing after it. The two birds proceeded to play
cat and mouse over Schenley Plaza (almost hitting Posvar Hall) before the
Merlin managed to shake the Peregrine falcon loose. The Peregrine
proceeded to soar and watch from overhead as I watched the Merlin chase a
chickadee over the plaza. It eventually left the area unsuccessful after
the Peregrine began to descend again from its lofty position.
Definitely an exciting day in Oakland!
Our club President, Connor Higgins, arrived a minute too late (he's quite
sour about that)after I alerted him about the chase.
University of Pittsburgh
Birding and Ornithology Club
Doesn't the merlin resemble a peregrine! No wonder E2 had his dander up!
Also, at lunchtime today Karen Lang and I saw an adult red-tailed hawk eating a pigeon on the lawn by Heinz Chapel while one of the peregrines watched from above.
And... Dan Yagusic saw a peregrine falcon at the 62nd Street Bridge around noontime.
AND... a very rare falcon visited Pennsylvania yesterday: A white-morph gyrfalcon flew by Waggoner's Gap Hawk Watch, north of Carlisle!
Update on Wed 12/8/10: Tony Bledsoe saw the merlin fly by Langley Hall at 11:30am.
The Pitt peregrines are at home but not particularly active. Karen Lang and I consider it a good day when we see both Dorothy and E2 at lunch time, but it's too cold to linger outdoors and watch them do nothing.
Six months ago we were having lots of fun tracking the "juvies" such as this one swooping off St. Paul's Cathedral steeple.
To feed my peregrine addiction -- and to provide the Aviary with some photos for their exhibit -- I built a slideshow of 2010 Peregrine Nesting Season Highlights.
Click on the photo above to watch the slideshow and feed your peregrine addiction. 😉
It's all white with dark eyes and a thick black bill that's blue at its base. In flight it's buoyant and erratic with quick changes in direction and speed. Perhaps this gave it a second name: fairy tern. In Hawaii it's called Manu-o-ku.
White terns eat saltwater fish and nest by the ocean but they never build a nest. The female lays only one egg per clutch in whatever suitable depression she can find. This could be on gravel, rock, or -- most amazingly -- on a tree branch. Imagine this: an egg sitting all by itself on the branch of a tree. Click here to see what this looks like!
If the egg isn't blown off the tree, it stands a good chance of surviving because it's in a sneaky place. Both parents incubate, brood and feed the chick and when it's independent in two months' time, its mother may lay another egg on the same tree branch and start the process all over again. In this way white terns can raise up to three chicks per year.
Their crazy nest site selection must work. White terns are listed as "Least Concern" on the IUCN Red List with over 100,000 breeding pairs worldwide.
(photo from Wikimedia Commons. Click on the photo to see the original.)
Red-tailed hawks eat squirrels but red-shouldered hawks, like this one, are a little too small to make squirrels a normal part of their diet. Perhaps this squirrel knew that.
A few years ago Steve Gosser saw an immature red-shouldered hawk perched quietly in his parents backyard. While he watched, a gray squirrel climbed the tree and made a beeline for the hawk. Did the squirrel want to challenge the hawk? Who would win?
When the squirrel got too close, the hawk puffed open his wings.