ANATOMY OF BIRDS
GEOGRAPHICAL DISTRIBUTION
MIGRATIONS OF BIRDS
CLASSIFICATION OF BIRDS
LIZARD-TAILED BIRD
AMERICAN TOOTHED-BIRDS
THE OSTRICHES
THE RHEAS
EMEUS AND CASSOWARIES
THE TINAMOUS
THE KIWIS
THE PENGUINS
LOONS AND GREBES
ALBATROSSES & PETRELS
STORK-LIKE BIRDS
GOOSE-LIKE BIRDS
FALCON-LIKE BIRDS
FOWL-LIKE BIRDS
CRANE-LIKE BIRDS
PLOVER-LIKE BIRDS
CUCKOO-LIKE BIRDS
THE ROLLER-LIKE BIRDS
SPARROW-LIKE BIRDS
Birds and Birding's Guide to:
Watching GEOGRAPHICAL DISTRIBUTION OF BIRDS
Temperature effect on Bird Distribution
Of the causes controlling or influencing distribution it is generally admitted that temperature and humidity are the chief factors, and, according to Merriam,”it has been found in the case of mammals and birds that the effects of temperature, estimated numerically, are more than three times greater than the effects of humidity upon genera, and many times greater upon the higher groups.”While there is some difference of opinion as to the exact period during which temperature exerts the greatest influence,”there can be but little doubt that for both animals and plants it is the season of reproductive activity."
There are various other factors, aside from those already mentioned, that are known to exert a greater or less influence on geographical distribution. The character of the soil, which carries with it an effect on the plant and insect life, may be mentioned, as well as the mechanical purity of the atmosphere as evidenced by the prevalence of fogs, etc.
Deforestation, the usual mark of the advent of civilization, has quite markedly affected distribution, and the extension of cultivated areas by means of irrigation over lands previously arid has increased the habitable areas for some species, and has also resulted in displacing many indigenous forms.
Mountain ranges have often been considered to be efficient barriers against distribution, and that they have an effect is true, but it is mainly the effect of altitude and temperature; for if conditions are similar on opposite sides of a range, they will usually be found inhabited by the same forms, which may have reached these positions by passing around the extremities of the mountains or by means of passes through them.
The real barrier is climate and not mass. Thus both sides of the Rocky Mountains as well as the high Sierra in California, are found to be inhabited by the same species of birds, and, says Merriam: “The great Himalaya has little or no influence in bringing about the really enormous differences that exist between the faunas and floras of the plains on its two sides, for these dissimilarities are due primarily to the great difference of temperature resulting from unequal base level, the Thibetan plateau on the north being several thousand feet higher than the plain on the south."
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