Once endangered, now threatened: Wood Stork over Wakodahatchee Wetlands, Delray Beach, Florida, by snooked.

Since 1967, 120 bird species have been listed as endangered or threatened under the Endangered Species Act of 1973 and the Endangered Species Preservation Act of 1966. How have they fared while protected?

To find out, the Center for Biological Diversity analyzed nearly 2,000 scientific reports for 93 currently listed species for which population data were available for at least 10 years. For the continental United States, 72 percent increased in numbers, while another 13 percent remained stable.

The success rate was lower for listed birds in the Pacific Islands (Hawaii, Guam, Palau, and the Northern Mariana Islands), where 34 percent increased and 27 percent remained stable.

The report noted the difference was likely due to multiple factors, including more serious threats from mosquito-borne diseases and invasive predators, and funding levels that are lower than those for mainland species.

The authors also compared the trends for 38 threatened or endangered species to 210 habitat-sensitive but unprotected species in the continental U.S. based on data from the latest State of the Birds report published in 2014. A larger percentage of protected species had increasing or stable numbers compared to unprotected species — 84 percent versus 50 percent.

Population trends for protected species revealed that it has often taken 10 or more years for numbers to begin to increase from the declines usually present when listed. This is not unexpected, as conservation measures often take time to identify and implement.

Recovery plans typically outline goals that span decades. According to the report’s authors, the recovery rates and successes of the Endangered Species Act indicate that the legislation is working as intended, protecting birds and wildlife for future generations. — Julie Craves

A version of this article appeared in the October 2016 issue of BirdWatching.

A Wild Success: A Systematic Review of Bird Recovery under the Endangered Species Act (Center for Biological Diversity).

Study: A third of North American bird species need urgent conservation action.

Birds protected by the U.S. Endangered Species Act.

Elfin-woods Warbler added to endangered species list.

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