India, Sept. 13 -- The great migrations of the world are dwindling.

The mule deer is stumbling upon new oil wells along its ancient route, and watching helplessly as the greenery it once chased retreats ahead of it, and the icy Wyoming winter sets in.

Wildebeest, hemmed in by roads, railways, gas pipelines, farms and housing, are halting what is arguably the world's most dramatic migration.

Birds, insects and the monarch butterfly are similarly finding themselves buffeted by new winds, stalled by a shifting Spring, or simply marooned, without the forests or host plants they had travelled all that way to meet.

The results are dramatic and far-reaching.

Forest fires in Africa. And dying baby giraffes.

Changes in bird diets in the Arct...