A staggering 22% of migratory animals are facing potential extinction, while some 44% are experiencing notable population decline, according to a "State of the World's Migratory Species" report released by the U.N. last month.
"This is the first-ever comprehensive assessment of migratory species," Executive Director Inger Andersen of the U.N. Environment Programme said of the report, which FOX Weather reported at the time.
"And it shows how our behaviour – unsustainable human activities – are jeopardizing the future of these species, and by extension, the future of other species and humanity itself," Andersen continued.
Here's a closer look at a few of the hardest-hit species, how they migrate and what the future may have in store for them.
1-IN-5 MIGRATORY ANIMALS FACE EXTINCTION, FIRST UN REPORT OF ITS KIND SAYS
Leatherback turtles are known for their diverse habitats and remarkably long migration routes – aquatic treks upward of 10,000 miles aren't uncommon for them, and depending on the season, they're equally likely to be spotted in Caribbean waters as they are to be seen off the frigid coasts of Russia and Alaska.
However, such a broad-ranging species is also open to broad-ranging threats. Classified as vulnerable – which, while concerning, falls short of the far more dire "endangered" label – by the International Union for the Conservation of Nature, leatherbacks are jeopardized by gradually warming waters, light pollution, poaching and accidental ensnarement in fishing nets.
Sand tiger sharks are known as top predators in their wide-ranging natural habitat, making appearances in the coastal waters of some 50 countries.
While historically not known to kill humans, a recent spike in attacks – particularly off the coast of New York – means 13 of the 36 unprovoked attacks by sand tigers have occurred over the last two years.
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Despite their prolific, domineering nature – and their recent notoriety – sand tigers are listed as critically endangered by the IUCN, one classification short of effective extinction.
Aggravating factors include fishing, pollution and habitat loss, on top of the species' unusually infrequent and low-yielding breeding patterns – sand tigers don't breed annually, and only bear up to two pups at a time.
Monarch butterflies writ large are classified as "least concern" by the IUCN – however, the status of their migratory subspecies, known to flock to Mexico each winter from the U.S. and Canada, fluctuates between vulnerability and outright endangerment.
MONARCH BUTTERFLIES WINTERING IN MEXICO AT SECOND-LOWEST LEVEL ON RECORD
Monarchs' short lifespan also means that no single butterfly completes the entire migratory process – so their annual southward trek is considered one of nature's more curious phenomena.
However, Mexico has reported a decreasing monarch presence over the past few winters; last year saw a 22% drop over 2022, and this year saw a 59% drop over last – meaning monarchs are wintering there at the second-lowest rate ever recorded.
Humans are responsible for some threats to migratory monarchs, including deforestation and ensuing habitat loss, as well as usage of lethal pesticides. However, naturally occurring factors like heat, droughts and other phenomena also contribute significantly.
In the U.S., migratory monarch populations have seen a significant rebound, with some 330,000 wintering in California last year, up from 247,000 in 2021 and fewer than 2,000 in 2020 – an indication that endangerment doesn't necessarily spell doom for a species, and a potential testament to the success of conservation efforts.
