A British red kite emerges from an aviary in the remote hills of western Spain and takes flight. At six months old, this is its first taste of freedom.

Without a sound, it soars high in the sky above scrubland and within seconds disappears from view into a wooded valley in the distance. It is the latest release in a conservation story that has come full circle.

Nearly four decades ago, the birds were extinct in England and Scotland with just a few pairs left in Wales.

In the late 1980s and early 1990s, red kite chicks from Spain and Sweden were released in the Chilterns on the Oxfordshire-Buckinghamshire border.

It proved so successful that the species is now thriving across the UK, with estimates of more than 6,000 mating pairs or about 15% of the world's population.

Dr Ian Evans, from Natural England, was one of the early pioneers. There were a lot of unknowns. The first lot we released, we thought they might just die or they might just move away. In 1991, we had our first breeding pairs and that was really an eye-opener because we thought 'well, this can be successful'. That was the springboard for establishing other release sites in England and Scotland.

British-born red kite chicks have now been taken to south west Spain as part of a four-year project to revive the population there from the brink of extinction.

The region has fewer than 50 mating pairs due to predators like the eagle owl and human factors such as illegal poisoning and electrocution. In 2022, conservationists were granted special licenses from Natural England to collect red kite chicks, mostly from Northamptonshire, and send them over to the Extremadura region of Spain.

More than 120 chicks have been collected, with about 30 exported each year.

The chicks are flown to Madrid and then transported 240 miles (385km) south to a wildlife hospital in Villafranca de los Barros, run by Accion por el Mundo Salvaje (AMUS).

Each chick has to be weighed, measured and tagged before being fitted with a GPS backpack which allows experts to track them.

The birds then move to holding aviaries for acclimatization before being released into the wild. Upon release, there's a mix of excitement and anxiety as conservationists hope the young kites adapt to their new life.

The mortality for raptors in general is really high during the first years of their life, says field technician Sofia Marrero. So now it's a little bit hard because you already know that some of them may not get to sexual maturity, so it's a bittersweet moment.

Despite the challenges, this project is a hopeful step towards reviving the red kite population in Spain and further enriching conservation efforts worldwide.