Fish, sea turtles, elephants, sharks, shorebirds and more of the world's migratory species are in dire decline, according to the first-ever State of the World's Migratory Species report from the United Nations, Ednews reports the following citing ABC news.

"This report showed us for the first time, in a very sobering way, that across the globe, over half the species that migrate are in decline. And that's largely because of human activities," Mark Hebblewhite, professor of wildlife ecology at the University of Montana, told ABC News Monday. "Migration allows animals to achieve greater numbers. So if we lose migration, we lose lots of numbers of animals."

Approximately 44% of migratory species across the world are in population decline and more than 20% of migratory species face extinction, according to the U.N.'s report, published Monday.

Migratory species are defined as wild animals whose entire population, or any geographically separate part of the population, periodically and predictably cross one or more national jurisdictional boundaries at different times in their lifecycles, according to the U.N.