UAE scientists are monitoring the movements of two rare falcons released into the wild in May this year.
The birds were among a batch of 66 falcons released in a remote area in Kazakhstan six months ago by staff at the Sheikh Zayed Falcon Release Programme.
Nine birds - five Saker and four Peregrine falcons - were fitted with satellite transmitters so scientists could follow them through the Central Asia steppe, but signals from seven have since been lost.
One of the remaining two birds, a Peregrine falcon, has travelled for more than 12,000 kilometres.
It set off in a north-westerly direction from Kazakhstan before turning around and flying the length of Russia, reaching the far north-eastern corner of the country before returning south back to Kazakhstan for its winter migration.
The bird, donated to the programme by the royal court of Bahrain, is in Uzbekistan.
The second bird still being monitored is a Saker falcon, which has remained in Kazakhstan. It has so far covered a distance of almost 5,000km.
Signals from the other seven birds were lost, which could mean they have either removed their transmitters, or that the transmitters are no longer working.
It could also mean that the birds have died.
Mohammed Al Bowardi, the managing director of the Environment Agency - Abu Dhabi, said the data from the two birds was of great value as both were from species that are threatened in the wild.
"The data we receive from the falcons we release is an essential element of our long-term strategy for ensuring healthy wild populations of these birds in the future," said Mr Al Bowardi. "This year's release has been fascinating with one bird travelling 12,755km, which has provided excellent information on migration patterns."
The Sheikh Zayed Falcon Release Programme is based in Abu Dhabi and works with partners in Morocco, Kazakhstan and other countries known to have suitable habitats for the falcons.