The last time anyone saw a confirmed Kauaʻi ʻōʻō was in 1987.

Now, over 35 years later, the U.S. Fish and Wildlife Service has acknowledged the once-flourishing Hawaiian bird is extinct, and removed it, along with 20 other species, from the Endangered Species List. You can still, however, hear the animals' now haunting song.

Biologist Jim Jacobi used a tape recorder to capture the call from either the last or one of the last Kauaʻi ʻōʻō at the high elevation Alaka'i Swamp on Kauai in 1986. Press play to hear the recording, preserved and uploaded to the web by the Cornell Laboratory of Ornithology’s Macaulay Library, below.

"It is known to be one of the finest singers of the Hawaiian birds with a variable and echoing song," the Fish and Wildlife Service said.

SEE ALSO: Scientists declared these animals extinct in 2021

Yet, crucially, this song is incomplete. It's only half a duet — there's no response.

"We have no way of knowing if this was the very last bird, but it’s hard not to listen as if it were," wrote Hannah Hunter, a PhD student at Queen’s University in Kingston, Ontario, who researches recorded sounds for species that are extinct, or may be extinct.

The Kauaʻi ʻōʻō was once omnipresent on its island, Kauai. "In the 1890s, these birds could be seen from sea level to the highest mountains, but if [the bird] exists, it is now restricted to the very remote areas where humans seldom enter," the Fish and Wildlife Service previously explained.

Island species are particularly vulnerable to extinction, as they often exist nowhere else. The Kauaʻi ʻōʻō, a black bird with distinctive yellow leg feathers, fell victim to the common culprits of habitat depletion (their homes were replaced by colonizers' crops like sugarcane), disease, and predation by invasive species.

The U.S. government listed the Kauaʻi ʻōʻō as endangered in 1967. By then, the species' numbers had almost certainly dwindled to unsustainable levels. Other recently delisted species met the same fate.

"Federal protection came too late to reverse these species’ decline, and it’s a wake-up call on the importance of conserving imperiled species before it’s too late," Fish and Wildlife Service director Martha Williams said in a statement. "As we commemorate 50 years of the Endangered Species Act this year, we are reminded of the Act’s purpose to be a safety net that stops the journey toward extinction. The ultimate goal is to recover these species, so they no longer need the Act’s protection."

A rare picture of a Kauaʻi ʻōʻō, taken by a U.S. Fish and Wildlife employee. Credit: USFWS / Robert Shallenberger

So far, the law has prevented the extinction of some 291 species, and recovered dozens from their endangered status. And that's with the vast majority of endangered species receiving under 25 percent of the funding needed to recover their populations.

Today's extinctions are happening "at least tens to hundreds of times higher" than extinctions occurred over the past 10 million years, the UN concluded in a major 2019 report.

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What can you do to fight extinction?

Today, over 1,500 endangered or threatened species remain on the Fish and Wildlife Service's list. But we're not helpless. You can make a difference, too.

• Help endangered species where you live: Conservationists suggest putting pressure on cities or local governments to protect dwindling species. For example, there are mussels on the brink of extinction in Big Darby Creek outside of Columbus, Ohio. But the local government wants to increase wastewater runoff into the creek. "The fate of the mussels is in the hands of these city planners," Tierra Curry, a conservation biologist at the Center for Biological Diversity, an organization that works to protect endangered species, told Mashable in 2021. "It's extinction playing out in real time."

• Have a cat? Keep it indoors: Domestic cats slaughter birds. "We could save a huge number of birds," the bird biologist Nico Arcilla told Mashable in 2019. Arcilla noted that cats are either the number one or number two killer of birds in North America. "Just one person keeping their cat indoors can save hundreds, maybe thousands, of birds. That’s a no-brainer."

• Have a yard? Plant native plants: Lawns are ecological disasters. But native vegetation is habitat for diverse life.