Shape
Most bird eggs have an oval shape, with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointy end develops at the back side. Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.
The shape has biological significance. A pointed egg will tend to sit on its side, with the big end tipped upward. The big end contains the air sac and its shell is pierced by a higher density of pores than the more pointed end. Tipping the big end upwards improves oxygen flow to the large head, with the physiologically demanding eyes and brain, that develops in the big end while the tail develops at the more pointed end.
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Classic oval bird egg (Vanellus spinosus)
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Almost spherical bird egg (Senegal Parrot)
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Long, "elliptical" bird egg (Loon)
Read more about this topic: Bird Egg
Famous quotes containing the word shape:
“his fear of the word “veil”;
and in the shape of a ship,
still another who slept.”
—Joáo Cabral De Melo Neto (b. 1920)
“somewhere in sands of the desert
A shape with lion body and the head of a man,
A gaze blank and pitiless as the sun,
Is moving its slow thighs, while all about it
Reel shadows of the indignant desert birds.”
—William Butler Yeats (1865–1939)
“The poet will prevail to be popular in spite of his faults, and in spite of his beauties too. He will hit the nail on the head, and we shall not know the shape of his hammer. He makes us free of his hearth and heart, which is greater than to offer one the freedom of a city.”
—Henry David Thoreau (1817–1862)