Tiny endangered tiger cubs from Siberia have been kitted out with radio collars so that scientists can track them.
The team had to wait until the cubs' mum had left the den before tagging them
They are the youngest tigers to wear the special elastic collars, says the Wildlife Conservation Society (WCS).
The cubs, all under six months old, were fitted with the gadgets at the Sikhotr-Alin Reserve in Russia.
With about 50% of Siberian cubs dying in their first year, the collars should help researchers find ways to improve the animals' survival chances.
It is thought there are only about 400 Siberian tigers left in the wild, with poaching for their skins and body parts one of the biggest threats to their existence.
"Through radio telemetry, we've learned a great deal about the needs of Siberian tigers, animals so elusive that few field researchers have seen them in their natural habitat," said John Goodrich, a WCS researcher and the head of the Siberian Tiger Project.
"Now we can finally get some idea of what causes the deaths of tiger cubs, which suffer a mortality rate of nearly 50% in their first year.
The playful cubs are the third generation to be tagged
"If we can somehow improve their chances, we can make a big difference in helping the population to grow."
Made from elastic, the tiny collars are big enough to fit a domestic cat, and have been specially designed so that they will eventually stretch and fall off as the cubs grow.
They give off a "mortality" signal whenever the tigers are inactive for more than an hour.
This means researchers can react swiftly and find them, which is crucial if they want to find out what killed them.
Toni Ruth, a WCS researcher, had designed and developed the collars for mountain lion cubs she was monitoring in Yellowstone National Park, US.
"The transmitters we use have a lifespan of 18 to 21-and-a-half months," she told BBC News Online.
"The limitation in how long the collar will remain on the cat will be how quickly the cat grows and puts pressure on the inner elastic.
"Also, the elastic may rot through more rapidly in a moist environment versus a dry environment," she said.
Although the collars are small compared with those worn by the adults, the signal range on the transmitter is similar to the larger ones because the antenna extends through the top of the collar.
Far from getting in the cubs' way, the antenna also makes for a good toy.
"The wavy antenna end makes a nice toy for siblings, so the antenna does receive a lot of wear and tear, which eventually can reduce signal reception," said Dr Ruth.
Before the collars were fitted, the cubs had to be located. The research team did this by tracking a previously collared three-year-old tigress called Galia who led them to her rocky den on the slope of a hill.
Dr Goodrich and his team had to wait until she had left the den, and her radio signal was weak, until they installed the transmitters on her young ones.
The den was found amongst rocks on a hill slope
Fur and blood samples were also taken for genetic and disease analysis.
The cubs are the third generation, stretching over 10 years, to be collared with radio transmitters.
Their mother, Galia, and their grandmother, Lidia, were tagged and tracked by the WCS team several years ago.