India, Sept. 14 -- T he 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 Arctic, and desperate new flight schedules. A sad silence in California, where once there was the hum of millions of winged things. The United Nations 2024 State of the World's Migratory Species report found that nearly half of the world's migratory species are on the decline, with migrations shrinking too. Even as human activity disrupts these ancient ways of life, efforts are underway to help. A multinational initiative is working to clear at least parts of the Egyptian vulture's massive arc (40 countries and three continents) of wind farms, power lines, poachers and poisoned bait. A reserve in Mexico seeks to offer safe haven to the monarch butterfly. (Read the stories alongside for more on this and other such efforts.) Meanwhile, we are still learning how little we know. It was only last year that a comprehensive aerial survey of war-torn South Sudan revealed that the largest land-mammal migration on the planet isn't the sea of movement formed by wildebeest in the Serengeti-Mara region of Kenya-Tanzania but rather what is now being called the Great Nile Migration, which involves gazelle, buck, antelope and a range of other species, amounting to six million animals, galloping from the Boma Badingilo Jonglei landscape in southeast South Sudan to the Gambella National Park in Ethiopia. The Great Nile Migration still isn't the largest on Earth by volume. That tag, for now, goes to the 10 billion tonnes of zooplankton that swim to the surface of our oceans every night to feed, in what is called a diel vertical migration. There is so much we don't know. Read on for a bit more, on what we do....