Dangling from a helicopter with a high powered rifle, a Kenyan vet fires drugged darts at elephants to sedate them so they can be fitted with satellite collars.

Ten minutes after the elephant is darted, the lumbering creature stumbles, and falls asleep. Ground teams are scrambled, rushing to the scene with just a 20 minute window to conduct tests and fit the collar before it regains consciousness.

More than 12,000 elephants live in Tsavo Park, threatened daily by poaching, but also more recently, by the construction of a new high-speed railway linking Kenya's coast to the capital.

The new 483-kilometre (300-mile) train route linking Kenya's Nairobi to the country's main port Mombasa is worrying conservationists, who fear the new infrastructure slicing through the giant Tsavo national park will affect the movement of elephants.

It is hoped that the satellite radio tracking collars fitted last month by the Kenya Wildlife Service (KWS) and conservation group Save the Elephants, will help conservationists monitor railway crossing points to allow the animals to live in peace.

"This project is the first of its kind in Kenya and indeed in Africa," said Dr. Benson Okita, head of monitoring at Save the Elephants. "It seeks to understand how elephant movements are influenced by a major infrastructural project."

Once the railway is complete, a six-lane motorway is also planned, so understanding what impact the railway has on the animals will be crucial to limiting the disruption caused by a new road.

Tsavo, spread over a western and eastern park, covers a vast 20,812 square kilometre (8,035 square miles) area of dense bush, about the size of Slovenia or Djibouti.

- 'First of its kind' -

Each collared elephant is tracked on a map overlaid with land use, logging their movements as humans encroach ever closer on wilderness areas, helping experts to monitor the impact on elephant ranging patterns.

The elephant movement data "will allow the country to secure space for wildlife as the Kenyan population grows," KWS deputy director for conservation Patrick Omondi said.

Though only elephants are being tagged, the scheme will help experts monitor the movements of other species as well.

"We are only using elephants, as a keystone species, but that will give an indication on how this effects wildlife distribution in general," said Sospeter Kiambi, who heads the KWS elephant tagging programme.

With ivory commanding thousands of dollars per kilo in Asia, conservationists have warned that African elephants could be extinct in the wild within a generation. More than 30,000 elephants are killed for their tusks every year.

Later this month, Kenya is due to set fire to the vast majority of its ivory and rhino horn stockpile -- some 105 tonnes of ivory, seven times the size of any ivory stockpile destroyed so far, as well as 1.35 tonnes of rhino horn -- in a highly publicised symbolic gesture against poaching led by President Uhuru Kenyatta.

The mass burning is expected to be attended by international celebrities, actors, conservationists and heads of state.

And though Kenya is striving to secure its economic future with infrastructure investment like the Mombasa-Nairobi road and rail link, it is hoped that the elephant tracking project will ensure that development does not come at the cost of wildlife.

- Environment vs Economy-

Kenya launched in 2013 the construction of a Chinese-funded $13.8 billion (10 billion euro) flagship railway project to dramatically increase trade and boost the east African country's position as a regional economic powerhouse.

The key transport link is eventually hoped to extend onwards to landlocked Uganda, and then connect with proposed lines to Rwanda and South Sudan, a key goods route extending far into the continent.

It replaces a colonial-era 19th century railway built under British rule, a line dubbed the "Lunatic Express" due to the logistical challenges -- including in Tsavo, where man-eating lions hunted the struggling railway workers.

Chugging once-a-day trains on that slow moving line occasionally hit animals, but posed nothing like the threat the busy, fast new link may pose.

Elephants crossing are being built underneath the railway -- raised bridges allowing animals to move beneath -- but concerns remains especially as to the impact of the planned road.

Similar raised bridges will be used when the railway line cuts through the 117 square kilometre (45 square mile) Nairobi national park, where buffalo, lion and rhino roam just seven kilometres (four miles) from the bustling high-rise city centre.

Construction of the railway in that park -- disturbing animals and with reported gaps made in fencing amid the building -- is reportedly one reason for a spate of lion escapes into the capital suburbs in recent weeks.

The new railway "is perhaps the most important transport project Kenya has seen since the building of the first railway in the early 20th century," said Iain Douglas-Hamilton, founder of Save the Elephants.

"If research such as this can help influence the way development is carried out, then we are truly on the path to securing a future for wildlife into perpetuity."