Birds are a group of warm-blooded vertebrates constituting the class Aves, characterized by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. There are about ten thousand living species, more than half of which are passerine, or `perching` birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some water birds, have further evolved for swimming.
圖片編號:
187515736
拍攝者:
Trinhhuytho
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授權類型 | 尺寸 | 像素 | 格式 | 點數 | |
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標準授權 | XS | 480 x 360 | JPG | 13 | |
標準授權 | S | 800 x 600 | JPG | 15 | |
標準授權 | M | 2000 x 1500 | JPG | 18 | |
標準授權 | L | 2581 x 1936 | JPG | 20 | |
標準授權 | XL | 3265 x 2449 | JPG | 22 | |
標準授權 | MAX | 4392 x 3294 | JPG | 23 | |
標準授權 | TIFF | 6211 x 4658 | TIF | 39 | |
進階授權 | WEL | 4392 x 3294 | JPG | 88 | |
進階授權 | PEL | 4392 x 3294 | JPG | 88 | |
進階授權 | UEL | 4392 x 3294 | JPG | 88 |
XS
S
M
L
XL
MAX
TIFF
WEL
PEL
UEL
標準授權 | 480 x 360 px | JPG | 13 點 |
標準授權 | 800 x 600 px | JPG | 15 點 |
標準授權 | 2000 x 1500 px | JPG | 18 點 |
標準授權 | 2581 x 1936 px | JPG | 20 點 |
標準授權 | 3265 x 2449 px | JPG | 22 點 |
標準授權 | 4392 x 3294 px | JPG | 23 點 |
標準授權 | 6211 x 4658 px | TIF | 39 點 |
進階授權 | 4392 x 3294 px | JPG | 88 點 |
進階授權 | 4392 x 3294 px | JPG | 88 點 |
進階授權 | 4392 x 3294 px | JPG | 88 點 |