Scarlet macaws are among the most recognisable birds of the rainforest, yet their numbers are falling in many parts of their range. Researchers are now trying to change the future of the species by confronting a harsh pattern of parenting that leaves many chicks unable to survive.

Parker had not even opened his eyes when he was lifted out of his nest.

It was a Monday morning in November 2018 in Peru's Tambopata National Reserve, far inside the Amazon rainforest. The naked young chick was weak and undersized, scarcely longer than a person's finger. He was the youngest of four scarlet macaw chicks, which meant his chances of surviving in the nest were extremely small.

At the foot of the nesting tree stood Gabriela Vigo-Trauco, the Peruvian researcher responsible for removing him.

After more than 20 years studying these birds, Vigo-Trauco had learned that scarlet macaws often allow their youngest chicks to die from hunger. Her research found that nearly every third- and fourth-hatched chick in nests with several eggs dies, while roughly a quarter of second-hatched chicks also fail to survive.

For the birds, this severe behaviour may once have been an effective survival tactic. Today, however, it limits the recovery of a species already threatened by nest poaching and habitat destruction. In Mexico and Central America, these pressures have pushed one scarlet macaw subspecies close to disappearing.

In 2017, Vigo-Trauco began an unusual conservation effort, one that eventually brought her to Parker. She hoped wild scarlet macaw pairs could be persuaded to raise chicks that had been rejected in their original nests. If successful, foster parents could offer a new chance to vulnerable young birds in Peru and potentially strengthen conservation work across the species' range.

Scarlet macaws are hard to overlook. Their brilliant red feathers blaze against the green canopy, while their loud calls can be heard well before the birds come into view.

A female may produce as many as four eggs in a breeding season, although normally only one or two chicks leave the nest as fledglings.

"The parents, especially the female, would push the youngest chick aside," says Vigo-Trauco, co-director of the Peruvian conservation group The Macaw Society. The organisation first documented this pattern after placing cameras inside nests in 2007.

"The chick is cold and crying, and when the male arrives, he feeds the mother and the first and second chicks, while the third chick remains there calling."

The researchers found no evidence that older chicks were attacking the younger ones, and the pattern did not appear to depend on how much food was available. So what makes parents abandon their later-hatched offspring?

Vigo-Trauco thinks adult macaws struggle to care for chicks that are at very different stages of development. A gap of only four or five days between hatchings can create major differences in feeding needs, body size and even the warmth required in the nest.

Parents may have to make a difficult decision, she says. If they try to provide equally for every chick, they could put the survival of the entire brood at risk.

In the relatively strong scarlet macaw population of the Peruvian Amazon, losing younger chicks has less impact on the wider population. But in places where conservation teams are already fighting poaching and forest clearance, the death of even a few additional chicks can be serious.

Hand-rearing abandoned chicks is one possible answer. However, it can take from six weeks to three months before a chick is ready to fly. Captive-raised parrots also tend to have poor survival rates after release because they may not know how to find food, avoid predators or join wild flocks.

That led Vigo-Trauco and her colleagues to explore the use of wild foster parents.

After Parker was removed in 2018, the team fed him by hand at their field station for three weeks. The work demanded feeding him every two hours, day after day.

At the same time, researchers checked nests throughout the forest in search of a pair that could safely adopt him and teach him the skills needed to live in the wild.

Similar methods had previously been used by aviculturists breeding macaws in captivity, where nests are close together and chicks can be moved easily. The idea also drew on work with other wild parrots, including yellow-shouldered parrots in Venezuela during the 1990s.

On 22 December, Parker was placed in another nest. His foster mother, named Tambo, began grooming him almost immediately.

Several months later, Parker successfully fledged. He became the first fourth-hatched chick known to leave a wild nest in Tambopata during decades of monitoring.

The project recorded similar results with 25 other rescued chicks between 2017 and 2019. Another three chicks were adopted successfully but did not survive to fledge because of lightning, predation and illness.

By 2019, Vigo-Trauco had gained confidence in the process. "It felt like playing chess," she says, "moving pieces around and discovering what could work."

Still, fostering chicks in the wild comes with major obstacles.

The work is costly. During her three-year Tambopata project, Vigo-Trauco had funding for a 20-person team, accommodation, wages and specialist equipment. Such a large operation, she says, is difficult for other projects to reproduce.

It is also complicated in the field.

Rony García-Anleu, director of biological research for the Wildlife Conservation Society in Guatemala, helped pioneer fostering among Guatemala's last scarlet macaw populations and co-authored Vigo-Trauco's paper on the technique.

However, García-Anleu's team last placed a chick with foster parents in Guatemala in 2019.

Successful fostering depends on exact timing, he explains. Researchers may have to travel long distances through forest to locate a nest where a chick is at risk. They must then quickly find another pair with either an empty nest or a chick close enough in age for an adoption to work.

His team instead prepares young macaws in a large enclosure, where they learn to fly, feed and interact with other birds before being released.

In Costa Rica, scarlet macaws had also suffered heavily from deforestation and poaching by 1994. A conservation group led by Christopher Vaugh began protecting active nests, running education programmes in schools and installing artificial nest sites where natural cavities were scarce.

Those efforts helped halt the decline and rebuild the local population. According to Vaugh, the lesson was clear: conservation must address the underlying threats, particularly habitat loss and poaching.

Even with its limitations, wild fostering is now helping guide work with other parrot species in countries from Argentina to Central America, Vigo-Trauco says.

Since 2020, she has also been testing a revised method. Instead of hand-feeding chicks first, researchers move newborns directly between nests soon after they hatch.

The new strategy demands closer nest monitoring but reduces the amount of intensive care required for tiny chicks, making it less expensive. During the second year of the project, it had already shown promise: two nests containing chicks with large age differences were reorganised so each pair of parents could raise two chicks that were much closer in age.

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Vigo-Trauco believes the simpler method could make fostering practical in regions with fewer financial resources.

"It is encouraging that our relatively healthy population has allowed us to generate knowledge that can help others," Vigo-Trauco says.

As for Parker, he eventually left the nest and learned to fly. In September 2019, the team spotted him again: a healthy young macaw flying with his adoptive parents and foster sibling.

"It was a normal family," she says, "with two fledglings."