Researchers have found that scarlet macaws intentionally refrain from feeding their youngest chicks in most nests, even when there is enough food available. As a consequence, only one or two chicks typically learn to fly—this is known as fledging—despite nests having as many as four chicks.
Scarlet macaws are often regarded as symbols of loyalty and virtue due to their belief in lifelong partnerships. However, recent findings reveal that they exhibit preferential feeding behaviors towards their young, highlighting their strengths as mates yet shortcomings as parents.
Luckily, scientists at Texas A&M have devised a way to reduce mortality rates among the chicks due to this poor parenting.
Researchers from the College of Veterinary Medicine and Biomedical Sciences have found that in most cases, scarlet macaws specifically choose not to feed their youngest chicks, even when there is no shortage of food. This leads to only one or two chicks being able to fly and fend for themselves, despite having up to four chicks hatching in a nest.
“For years, it’s been known that scarlet macaws usually have more chicks than the number that survive to fledging,” explained Dr. Donald Brightsmith, a professor in the Department of Veterinary Pathobiology. “Our findings show that about 26% of second-hatched chicks and nearly all third and fourth chicks do not make it to fledging.”
“After testing multiple theories regarding the survival of these younger chicks, we concluded that it isn’t sibling rivalry or food scarcity that’s to blame. The parents simply stop feeding certain chicks, leading to their starvation,” he remarked.
The key issue seems to be the age differences among the chicks.
“Scarlet macaws tend to lay their eggs over several days rather than all at once, which causes the chicks to hatch at different times,” said Dr. Gabriela Vigo-Trauco, a post-doctoral researcher at the Schubot Center for Avian Health, who led the research. “If a second chick hatches just a few days after the first, it is likely to be fed. However, if it hatches four to five days later, the parents are less likely to feed it, resulting in its neglect and death.”
The researchers, whose work is published in the journal Diversity, believe that when chicks hatch several days apart, they have varying needs for parental care. For example, some chicks are still reliant on incubation while others require feeding, thus increasing the chances of neglect and starvation.
With these insights, the team has created a method to save the neglected chicks by providing them with “foster parents” among the macaw population.
“Fortunately, scarlet macaws are not endangered, but many parrot species face threats,” Brightsmith noted. “Our aim is for this foster program to aid the survival of endangered parrot species.”
Understanding Brood Reduction
Brood reduction, the practice of eliminating chicks post-hatching, is common among various bird species.
“For example, certain seabirds like boobies, gulls, and pelicans exhibit intense sibling rivalry that can lead to fatalities,” Vigo-Trauco explained. “Moreover, species such as eagles and falcons can attack and kill their own chicks, typically targeting the younger ones.”
In the case of scarlet macaws, starvation accounts for 45% of all chick deaths, with third or fourth-hatched chicks always succumbing.
“We sought to identify the reasons behind the 26% starvation rate among second chicks,” Brightsmith stated. “While scientists often attribute these deaths to resource scarcity, it’s puzzling that scarlet macaws lay so many eggs if conserving resources was the priority.”
To explore the availability of food, Gustavo Martinez, a team member, monitored trees in the forests of the Tambopata National Reserve in Peru to estimate the fruit supply, which is the main food source for scarlet macaws.
“Over several years, he regularly checked around 1,300 trees for fruits and flowers,” Brightsmith explained. “While we found instances when food shortages led macaws to skip breeding for a season, there was no connection to chick starvation.”
Catching Macaws In The Act
To observe the behavior of scarlet macaws in their nests, the researchers set up cameras in nest boxes across the Tambopata National Reserve for ten years. This allowed them to gather footage of what was occurring with the chicks.
They also manually examined the nests to determine which chicks had received food, confirming that neglect was intentional.
“Scarlet macaws have a crop, a food storage sac in their necks, which is easily visible in chicks when filled,” Brightsmith shared. “We filmed female macaws trying to provide excessive food to their oldest chicks while the third chick wandered around with an empty crop, begging for food.”
“Additionally, younger chicks cannot regulate their body temperature, making it essential for them to remain in the nest. Our observations revealed that mothers would not even share warmth with their starving offspring,” he continued. “As researchers, we strive to avoid anthropomorphizing—attributing human-like morality to animals—but it’s challenging to witness such neglect and not view it as parental abuse.”
The apparent “neglect” is further complicated by the fact that macaw parents may not be in sync.
“Occasionally, a female macaw might attempt to bury a chick she chose to ignore by kicking nest material over it,” Brightsmith elaborated. “However, the male might return, uncover it, and feed it. This creates additional complexity in the situation.”
Saving Neglected Chicks
While scarlet macaws demonstrate questionable parenting methods with their hatchlings, they are surprisingly effective foster parents for other neglected chicks.
As part of her doctoral studies, Vigo-Trauco created a program to save the neglected chicks. These chicks are initially raised in captivity for a few weeks before being placed in the nests of macaws with chicks at a comparable developmental stage or those that have lost all their chicks to predators.
This approach eliminates varying parental care requirements, allowing the foster parents to nurture chicks that would otherwise face starvation.
“The key to success lies in ensuring that all chicks appear similar in size,” she indicated. “This encourages the new parents to treat the foster chick as their own.”
Even though the macaws may notice a difference, this does not prevent them from adopting the foster chicks.
“Our cameras capture moments where they arrive at the nest box, peer inside, and seem to ponder, ‘Did I come to the wrong nest?’ It’s quite amusing,” Brightsmith laughed. “They tilt their heads for a better view of the new chick, take a moment to process, and then begin feeding it.”
The foster chick program, reported in the journal Diversity in 2021, successfully placed 28 chicks over three breeding seasons.
“Parrots rank among the most endangered bird groups globally,” Brightsmith added. “We hope that this program, along with our insights on brood reduction, can aid in the conservation of various parrot species across tropical regions.”