France, Feb. 12 -- The world's migratory species are under threat across the planet with their global risk of extinction increasing, a landmark UN report released Monday has warned.

Until now there has been no comprehensive data on the conservation status or population trends of the billions of animals that make yearly migratory journeys across the world's lands, seas and skies.

These species often rely on very specialised sites to feed and mate. Their journeys can cross international borders and even continents.

Iconic species that make some of the most extraordinary journeys across the planet include the monarch butterfly, the humpback whale and the loggerhead turtle.

The first-ever State of the World's Migratory Species report - wh...