JACKSON, Miss.— The U.S. Fish and Wildlife Service proposed today to remove Endangered Species Act protection from the interior least tern, a small bird that nests along major rivers in the Midwest and southern United States.

Endangered Species Act protections have helped interior least tern numbers expand nearly tenfold over the past three decades. The tern would be the 45th species to be delisted for recovery in the United States, including 21 in the past five years.

“The Endangered Species Act brought these tiny terns back from the brink,” said Noah Greenwald, endangered species director at the Center for Biological Diversity. “This is another example of how well this landmark law works to save wildlife that’s at risk of vanishing. Protecting these pretty birds has also helped us move toward managing rivers to more closely mimic natural flows, benefiting many other species and river health.”

The tern’s recovery announcement comes months after the Trump administration finalized rollbacks to key Endangered Species Act regulations. The changes could lead to extinction for hundreds of animals and plants.

“Trump officials are mangling a law that has been critical to rescuing these birds and so many other species,” Greenwald said. “If we don’t save the Endangered Species Act from Trump, it won’t be able to save our imperiled plants and animals anymore.”

The fish-eating least tern is the smallest of North American terns. Least terns in the interior population prefer nesting on open sandbars near wide river channels. They occur along major midwestern rivers such as the Missouri, Mississippi, Ohio and Arkansas, along the Red River in Louisiana, and on the Rio Grande River in New Mexico and Texas. They winter along coastal areas of Central and South America and the Caribbean Islands.

Before being protected as endangered in 1985, the number of interior least terns had plummeted below 2,000 birds. This was caused by changes to river systems from dams, dikes, reservoirs and water diversions, which eliminated most historic least tern nesting habitat.

Natural wide channels dotted with sandbars have been replaced by narrow, armor-banked rivers with highly altered flows. The spread of invasive plants also reduced suitable tern nesting habitat. Recreational activities on rivers and sandbars can disturb nesting terns, causing them to abandon their nests.

But least terns have proven resilient to habitat changes and have benefited from improved river management to create suitable habitat. The interior least tern population is now estimated at roughly 18,000 birds.

A 1990 recovery plan set an overall population goal of 7,000 birds, which has been exceeded since 1994. Tern population size targets for recovery have been met in the Mississippi, Red and Arkansas river drainages, but not yet in the Missouri drainage, perhaps the most heavily impounded and managed of the rivers in the tern’s range.

The Lower Mississippi River hosts the largest numbers of interior least terns, due in large part to a more naturally functioning river system and periodic flooding. Large floods improve and restore sandbars used by terns as nesting habitat, support high production of fish eaten by terns and flood out mammalian predators of terns.

Tern counts in the Missouri River drainage continue to fall below the population target, because the river is highly regulated and dams interrupt the supply of sediments needed to build sandbars along rivers. Most terns in the Missouri watershed are found on the Niobrara, which is the least impounded of the tributaries.

Tern population targets have also not been met for the Rio Grande River drainage, but there have only been periodic and partial tern surveys there since 1985. There were no historical records of least terns from natural river segments in the Rio Grande River drainage, and all current populations occur in human-created or altered habitats.