The release of six critically endangered native birds on Mauna Kea in May was the latest chapter in a years-long effort to save the native species.

Six palila bred at San Diego Zoo Global’s Keauhou Bird Conservation Center were released on Mauna Kea’s northern slope May 19 and 20 in an attempt to establish a second population on the dormant volcano.

But it was not the first time the small yellow-and-green birds were released there.

Between 1997 and 2006, 188 palila were translocated from the main population on the mountain’s southwestern slopes to the northern slope, at Puu Mali. The goal of the U.S. Geological Survey project was to establish a backup population in case the main one became compromised. In addition, the Keauhou center released an additional 28 captively bred palila between 2003 and 2009.

But the transplanted palila population remained only until 2012. Many of the birds died — some due to predation — and others flew back to the southwestern slope.

Even so, the effort isn’t regarded as a failure.

“To a certain extent it was a success,” said Chauncy “Kala” Asing, project coordinator for the Mauna Kea Forest Restoration Project. “There was a new generation created by birds that were released on the mountain.” The Mauna Kea Forest Reserve Project reported that eight fledglings were produced.

Nevertheless, attempts to get palila to the northern slope ended, in part because of funding but also because the habitat was deemed unable to sustain palila, said Chris Farmer, Hawaii program director for the American Bird Conservancy.

“Until the forest is restored, we didn’t feel comfortable releasing these birds,” Farmer said. “Now we feel comfortable doing these releases.”

Aside from the translocation and release efforts on the northern slope, palila were more or less located only on Mauna Kea’s southwestern slope.

Today there are only about 1,000 palila left in the world, making up the entirety of the only surviving species of 16 finch-billed honeycreepers that used to exist on the main Hawaiian Islands.

“We know from fossil records that palila used to be on Oahu and Kauai, so they used to have a much wider distribution,” Farmer said. “By the time the Europeans were documenting things, it was only on that kind of interior part of Big Island.”

Food availability and habitat issues caused by unmanaged ungulates like goats and sheep, which have been destroying Mauna Kea’s forests since the late 1700s, needed to be addressed.

“Without the forest the birds can’t survive,” Farmer said. “That’s been the problem for decades, if not centuries, that the habitat was degraded by sheep and by other animals up there.”

Mauna Kea was also in the middle of a drought, Asing said, but that ended around 2015.

The Mauna Kea Forest Reserve Project, which was established in 2006, has since planted over 200,000 mamane seedlings over 600 acres on Mauna Kea, much of which used to be grazing lands.

Palila thrive on mamane seed pods, flowers and leaves, making up nearly all of their diet. Mamane are also the dominant species on Mauna Kea.

Still, the palila population has been declining rapidly over the past 20 years, dropping nearly 80% between 1998 and 2018, according to a recent study.

That decline has slowed during the last 10-year push to restore the forest on Mauna Kea, as palila numbers have started to stabilize. Thirty birds, including the six released in May, are set to be released on the mountain come July, Asing said, and another translocation effort will hopefully follow.

“Essentially, we’re just waiting for the species to rebound itself,” he said. “It’ll take a long time for the species to recover. The mountain itself is recovering, has been recovering slowly, but it’s looking awesome.”

Farmer is similarly optimistic.

“I think we can save palila,” he said. “I’m confident about that.”