Every year, mammals, birds, fish and insects make epic migrations between habitats. The humpback whale, famously, can travel 5,000 miles in a trip.

But because these animals cross national borders and frequently congregate at predictable way stops, they are uniquely vulnerable to human predation, pollution and habitat loss. As a result, one in five migratory species is at risk of extinction, according to a new report by the United Nations.

State of the World’s Migratory Species is a first-ever global survey focused solely on migratory species. The key findings are grim. Of the roughly 1,200 species already listed and protected under the U.N. Convention on Migratory Species (CMS), a 1979 global conservation treaty, 44% have declining populations. It’s even worse if you look at migratory reptiles, 70% of which are facing extinction, and fish, a shocking 97% of which are in danger of going extinct. Migratory species, a group that includes iconic animals such as Monarch butterflies, comprise a major food source for other wildlife and perform critical roles like pollination in ecosystems.

It’s clear that humans are the primary cause of this apocalypse, said Kelly Malsch, the report’s lead author and head of the species program at the U.N. Environment Program’s World Conservation Monitoring Center. While these species face many barriers to health, "there were two underlying threats, overexploitation and habitat loss, that were affecting most,” she said. "This includes direct exploitation like hunting and fishing but also indirect takings through bycatch or mist nests.” (Mist nets are hard-to-detect nets used to capture birds and bats or prevent them from accessing gardens and crops.)

The report is not the first to sound the alarm about the vast wildlife-extinction crisis facing the planet. The International Union for Conservation of Nature Red List of Threatened Species is perhaps the best-known inventory of all endangered species. But this is the first report solely on the status of migratory species, which face conservation challenges that require cooperation from multiple countries — the reason for creating the CMS in the first place.

While the researchers focused on species that are already being afforded legal protections — including jaguars, sea turtles and elephants — they also surveyed another 3,000 migratory species not on the CMS list, and found another 400 were endangered.

Technically, there are already strict limits on the hunting or capturing of species listed under the CMS, but there are many challenges to enforcing those protections. Migratory animals are also increasingly affected by the ravages of climate change, said Amy Fraenkel, the executive secretary of CMS. Fire and drought are cutting into habitats and warming is delinking the times of migrations from prime food availability, she said.

The goal of the survey was not only to point to the dangers facing species but to help identify crucial habitat areas that should be a priority for protection. Just under half of sites identified as important are now subject to some level of protection, the report says, but "many critical sites for CMS-listed species are yet to be mapped.”

If there is a silver lining, it is that some conservation partnerships have been successful at protecting individual species. Whaling bans, for example, enabled the western South Atlantic population of humpbacks to rebound from 450 individuals in the 1950s to 27,000 by 2019, close to their pre-whaling abundance.