Hawaii experts say two native bird populations have declined by more than half and could face extinction if nothing is done to save them, a report said.

The Maui Forest Bird Recovery Project said 312 Maui parrotbills and 2,411 crested honeycreepers remain in the wild, Hawaii News Now reported Friday.

Those are down more than 50% from previous population estimates of the two Hawaiian honeycreeper species, according to a new interagency monitoring report from the U.S. Geological Survey, Hawaii Division of Forestry and Wildlife, and other wildlife agencies.

"Without intervention, these changes are projected to cause population decline and additional extinction of the remaining Hawaiian forest birds," recovery project expert Hannah Mounce said.

Studies over the past several decades found there are multiple threats to these two endangered bird species, including disease and habitat degradation, wildlife officials said.

There are plans to reintroduce the parrotbills, also referred to as kiwikiu, to the Nakula Natural Area Reserve in the south and west regions of Maui in order to boost the endangered species' numbers, experts said.

In preparation for the reintroduction, more than 200,000 native plants were planted in the Nakula Forest Reserve and Kahikinui Forest Reserve 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.

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