Herds of caribou on the tundra, flocks of Swainson’s hawks above the grasslands—these are the great wildlife migrations of the U.S., and they are in danger. A new paper by WCS Senior Conservationist Keith Aune looks at the top five terrestrial and top three aerial migrations across the American West, and details the challenges they face.

Climate change, the paper indicates, is a leading threat and has the capacity to impact migrations in myriad ways, from the timing of flower blooms to the accumulation of snowpack. Other common threats Aune discusses include increased development, habitat loss, and human-made obstacles.

Learn more about endangered American wildlife migrations in this story from the New York Times.