The species, known by the scientific name Rhinoplax vigil, is listed as "critically endangered" by the International Union for Conservation of Nature.
"Currently, there are fewer than 100 of the birds in Thailand's forests," says Dr. Kaset Sutacha, chairman of the Bird Conservation Society of Thailand and head of the Exotic Pet and Wildlife Clinic at Kasetsart University's Faculty of Veterinary Medicine in Bangkok.
"Critically endangered" is just a step away from "extinct in the wild" and two steps from becoming considered "extinct."
Demand from China is helping drive demand for their distinctive casques, "helmets" in French, which males deploy in battle. The material is used to make rings, pendants and other decorative items.
Worries over the species' survival intensified after the wildlife trade monitoring group TRAFFIC recently posted photos online of dozens of skulls of the endangered avian for sale.
A campaign on the change.org online petition site is pressuring the government to add the bird to Thailand's Wildlife Preservation List as soon as possible. It now lists 19 other species.
The bird is already on Thailand's official list of protected animals, but would get much better protection if it's included in the Wildlife Preservation List, Kaset said.
That "means we can get money, officers and tools from the government, including a national conservation plan designed just for this species," he said.
The population of the bird, found in Indonesia, Malaysia and parts of Myanmar and southern Thailand, is dwindling, the IUCN says.
Most types of hornbills have hollow casques. The helmeted hornbills' are a hard, solid block that in the illegal wildlife market is called "red ivory."
The London-based Environmental Investigation Agency says black market prices are up to five times higher than for elephant tusks.
China appears to be the main market for helmeted hornbill parts and products, though there is also demand in Laos and Thailand, says Elizabeth John, TRAFFIC Southeast Asia's senior communications officer.
TRAFFIC has spotted at least 546 hornbill parts, mostly casques of helmeted hornbills, for sale on Thai Facebook groups in the past five years.
The Bird Conservation Society of Thailand has seen the number of helmeted hornbills depleted over the past 40 years by deforestation and climate change.
"If we let the poaching goes on, it will wipe out the entire species in Thailand in no time," Kaset said.
Preeda Tiansongrasamee, a researcher who has lived in Budo-Sungai Padi National Park in the Budo range in Narathiwat province for 20 years, said hunters traditionally sought helmeted hornbills' casques and heads because they were thought to bring good luck.
"In the past, we could see heads of the bird in homes and people wore amulets made from casques," he said by phone. "That belief has faded away, but a new group of poachers has emerged who hunt the bird to cater to demand from outside Thailand."
Traders will pay villagers 5,000-6,000 baht ($165-$200) for a hornbill head, Preeda said he was told. Prices are double or triple that in cities and increase exponentially when sold overseas.
Preeda walks through the forest every day to check on the hornbills.
"Right now, there are two nests that have baby birds inside. We have to pray that the male will be safe and bring back food every day," he says. "Otherwise, the mother and its babies will die."
Local loggers tend to heed appeals not to cut down trees with hornbill nests, but poachers from elsewhere tend not to listen and sometimes threaten people who try to stop them, Preeda said.
A longstanding Muslim insurgency has complicated efforts to save the birds, since the rebels sometimes target forest rangers they consider to be on the side of the government, their enemy.
The bird is so imperiled it's likely to be added to the Wildlife Preservation List, said Thon Thamrongnawasawat, a respected government consultant on conservation and development.
Last year, Thon got four species added to the list.
But implementing a conservation plan doesn't guarantee the species will survive, he said.
"It's not only the animals that we have to take care of. The people who live in the area should be looked after as well," says Thon.
"They have to survive and have a better life if they are to refrain from cutting trees, and poaching. Without cooperation from people, no conservation plan will last long."