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doi: 10.1038/019481d0
PROF. NEWTON in his article on Migration of Birds (NATURE, vol. xix. p. 433) has omitted one, and a very important limit to the height at which birds of passage can perform their journeys. This is temperature. The following table of Daniell's will show how little probability there is of migratory birds flying at great elevations, and that even in low latitudes, the temperature at altitudes exceeding four and a half miles would be prohibitory to the existence of the majority of migrants:—
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