Wildlife agencies say two native bird populations on Maui have declined by more than half and could face extinction if nothing is done to save them.

Fewer than 312 Maui parrotbills and 2,411 crested honeycreepers remain in the wild — 50% fewer than previous population estimates of the two Hawaiian honeycreeper species, according to a new interagency monitoring report from the U.S. Geological Survey, the state Division of Forestry and Wildlife and other agencies.

The two native endangered species are endemic to Maui and are found only within the surveyed area in the eastern part of the island.

Studies over the past several decades found multiple threats to the endangered birds, including disease, depredation and habitat degradation. Experts say introduced avian malaria is the most significant long-term threat to Hawaii’s native birds, and the disease is continuing to spread upward in elevation due to climate change.

“Without intervention, these changes are projected to cause population decline and additional extinction of the remaining Hawaiian forest birds,” said Hannah Mounce of the Maui Forest Bird Recovery Project in a news release.

There are plans to reintroduce the parrotbills, also known as kiwikiu, to the Nakula Natural Area Reserve in the southern and western regions of Maui this fall to boost its numbers, the release said. In preparation for the reintroduction, more than 200,000 native plants have been planted in the Nakula and Kahikinui forest reserves since 2013, covering thousands of acres.

“It is urgent that we move forward with the recovery efforts for these species. If we wait for much longer, we will not have these species left to save,” Mounce said.

Wildlife officials did not mention plans for the crested honeycreepers, also known as akohekohe.

Seth Judge, USGS wildlife research specialist and landbird monitoring coordinator with the University of Hawaii, noted the black-faced honeycreeper, or poouli, was the most recent Maui endemic forest bird to go extinct, in 2004, and based on the most recent survey, “the kiwikiu is next.”

The surveys conducted for the report were the largest and most comprehensive interagency effort to research East Maui native forest birds since 1980, the release said. The findings provide an update of forest bird population estimates and within Haleakala National Park and reserves managed by the forestry division.

Other partners in the monitoring report included the National Park Service and the University of Hawaii at Hilo.