By Alex Kirby
BBC News Online environment correspondent
The discovery of large flocks of threatened vultures in South East Asia is highly significant, say experts.
Vultures are important scavengers
The discovery of the sizeable groups in Indo-China was announced by BirdLife International and the Wildlife Conservation Society (WCS).
Most of Asia's vultures are in steep decline, with a common veterinary drug, diclofenac, blamed for their plight.
The drug is not used by Cambodian vets at the moment, raising hopes the birds may retain a foothold there.
The groups spotted included slender-billed and white-rumped vultures.
The vulture's tenuous grasp on survival has human health implications, as the carrion they eat can rapidly spread several diseases.
Rarest of them all
At one site in north-east Cambodia, BirdLife and WCS teams counted more than 120 birds, the largest single gathering recorded in the region for 15 years.
But they say the most significant observation was the sighting of a flock of at least 28 slender-billed vultures, the rarest of the Asian species.
The largest group previously sighted in Indo-China had numbered just four birds.
Populations of both the species seen recently and of the Indian vulture have fallen precipitously in south Asia in the last decade, especially in India, where numbers have declined by 97% since 1993.
The birds are poisoned when they feed on the carcases of cattle treated with diclofenac.
Dr Sean Austin of BirdLife said: "Fortunately the drug is not currently available for veterinary use in Cambodia, so presently there are relatively few barriers to successful conservation of vultures in this country.
"But they are threatened by a lack of available food, by direct persecution through hunting, through capture for the pet trade or for their perceived medicinal value."
The recent sightings happened during a training course to establish "vulture restaurants", places to provide the birds with food which have become tourist attractions in South Africa.
"Supplementary feeding of vultures is a relatively simple and effective conservation action for us to undertake," said Dr Austin.
"Given the catastrophic decline of vultures elsewhere in Asia, Cambodia could provide an important stronghold."
Rabies and anthrax
BirdLife, WCS and the Cambodian government have formed a working group to try to protect the vultures.
The ornithologists say priorities include a ban on diclofenac in key areas, and the promotion of suitable replacements.
They also want a monitoring programme to see how many vultures remain and what their population trends are, and protection for their breeding sites.
Among diseases which can spread more quickly in the absence of vultures are rabies and anthrax.