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A few hundred species migrate long distances, in some cases of thousands of kilometres. About 120 species of fish, including several species of salmon, migrate between saltwater and freshwater (they are 'diadromous'). [23] [24] Forage fish such as herring and capelin migrate around substantial parts of the North Atlantic ocean.
Of course, in the southern hemisphere, the directions are reversed, but there is less land area in the far south to support long-distance migration. [ 19 ] The primary motivation for migration appears to be food; for example, some hummingbirds choose not to migrate if fed through the winter. [ 20 ]
However, pixel shaders do have knowledge of the screen coordinate being drawn, and can sample the screen and nearby pixels if the contents of the entire screen are passed as a texture to the shader. This technique can enable a wide variety of two-dimensional postprocessing effects such as blur, or edge detection/enhancement for cartoon/cel shaders.
Bird migration is on the rise, and so are window collisions. As temperatures slowly drop in Chicago, 300 million to 400 million birds are crossing the continent heading south to their nesting ...
By the time they are ready to migrate, they are often so heavy they can barely fly. The timing of migration appears to be triggered by day-length only. This is why it is OK to keep feeders out ...
The mallard has hybridised with more than 40 species in the wild, and an additional 20 species in captivity, [13] though fertile hybrids typically have two Anas parents. [14] Mallards and their domestic conspecifics are fully interfertile; many wild mallard populations in North America contain significant amounts of domestic mallard DNA. [15] [16]
Most hummingbirds migrate in the winter to Central America or Mexico, but some hummingbirds spend the winter on the Gulf Coast and may be found in South Texas and South Louisiana during mild winters.
Domestic ducks are mostly promiscuous, where wild mallards are monogamous. Domestic ducks have lost the mallard's territorial behaviour, and are less aggressive than mallards. [7] [8] Despite these differences, domestic ducks frequently mate with wild mallard, producing fully fertile hybrid offspring. [9]