Nearly half of the world's migratory species are in decline, according to a new United Nations report released Monday.

Many songbirds, sea turtles, whales, sharks and other migratory animals move to different environments with changing seasons and are imperiled by habitat loss, illegal hunting and fishing, pollution and climate change.

About 44% of migratory species worldwide are declining in population, the report found. More than a fifth of the nearly 1,200 species monitored by the U.N. are threatened with extinction.

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“These are species that move around the globe. They move to feed and breed and also need stopover sites along the way,” said Kelly Malsch, lead author of the report released at a U.N. wildlife conference in Samarkand, Uzbekistan.

Habitat loss or other threats at any point in their journey can lead to dwindling populations.

“Migration is essential for some species. If you cut the migration, you’re going to kill the species,” said Duke University ecologist Stuart Pimm, who was not involved in the report.

The report relied on existing data, including information from the International Union for Conservation of Nature's Red List, which tracks whether a species is endangered.

Participants of the U.N. meeting plan to evaluate proposals for conservation measures and also whether to formally list several new species of concern.

“One country alone cannot save any of these species,” said Susan Lieberman, vice president for international policy at the nonprofit Wildlife Conservation Society.

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At the meeting, eight governments from South America are expected to jointly propose adding two species of declining Amazon catfish to the U.N. treaty's list of migratory species of concern, she said.

The Amazon River basin is world’s largest freshwater system. “If the Amazon is intact, the catfish will thrive — it's about protecting the habitat,” Lieberman said.

In 2022, governments pledged to protect 30% of the planet's land and water resources for conservation at the U.N. Biodiversity Conference in Montreal, Canada.