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Why Do Scarlet Macaws Neglect Their Youngest Chicks?
Scarlet macaws lay as many as four eggs per clutch, but only one or two chicks survive until fledging due to parental neglect.
Scarlet macaw in flight. (Credit: Zdeněk Macháček via Unsplash. NOTE: This image has been cropped.)
Zdeněk Macháček via UnsplashScarlet macaws are one of the most recognizable New World parrot species, and they are highly sought after as pets due to their brilliant plumage colors. These large colorful parrots are also widely celebrated for the long-term bonds they form with their mates. But they apparently do not form such strong bonds with their chicks.
A new study of wild scarlet macaws, Ara macao, living in Peru has documented what has long been known by aviculturists who work with captive-bred scarlet macaws: the parents neglect some of their chicks, allowing them to starve to death — even when there is plenty of food available.
A team of researchers based at Texas A&M University's college of Veterinary Medicine and Biomedical Sciences investigated to find out why.
"Scientists have known for years that scarlet macaws hatch more chicks than they fledge," said the study's senior author, Donald Brightsmith, an Associate Professor of Ecosystem Health in the Department of Veterinary Pathobiology. His research focuses on a wide variety of parrot topics including parrot conservation, clay lick use (read more here), nesting, movements, habitat use, etc. He also conducts research on the diets of captive and wild parrots, on parrot enrichment, and he also studies wild red-crowned parrots living in Texas (read more here and here).
"We found that 26% of second chicks in scarlet macaw broods and nearly all third and fourth chicks die before fledging," Professor Brightsmith reported.
This peculiar behavior also is seen in avicultural situations, unless people intervene by raising the 'extra' chicks themselves. Which raises the question: why is this happening? Are the young parrots attacking and killing each other? Are the parents responding to a lack of food by ignoring the cries of the weakest chicks?
"We tested several theories as to why these younger chicks don't survive, and we found that it's not sibling rivalry or a lack of food," Professor Brightsmith explained. "The parents just stop feeding certain chicks, so they starve to death."
How do the macaw parents decide which chicks to neglect? According to this study, it appears that the ages and body sizes of the chicks are the deciding factors, with the oldest and largest chick in a clutch benefiting from its parents' choice.
"Scarlet macaws lay eggs over a period of several days instead of all at once, which means the chicks don't hatch on the same day," said the study's lead author, Gabriela Vigo-Trauco, a post-doctoral researcher associated with the Department of Veterinary Pathobiology and the Schubot Center for Avian Health.
"If the second chick hatches only a couple of days after the first, there is a good chance that the parents will feed it," Dr Vigo-Trauco noted. "However, if it hatches four, five, or more days after the first chick, the parents will probably neglect it and let it die."
Considering that the average scarlet macaw brood usually consists of four eggs, this means that two otherwise perfectly healthy chicks in each brood are virtually guaranteed to starve to death, so there must be an evolutionary reason for this.
Professor Brightsmith, Dr Vigo-Trauco and collaborators suspected that scarlet macaw chicks require different sorts of parental care as they grow. For example, some chicks need feeding whilst others need incubating, which contributes to the high rates of neglect and starvation.
To reduce chick deaths, Professor Brightsmith, Dr Vigo-Trauco and collaborators developed a foster parent program for saving neglected chicks by adopting them out to other macaw parents. Without such interventions, 45% of all scarlet macaw chicks die from starvation, and chicks that hatch third or fourth in a brood always die.
But interestingly, some second-hatched chicks may survive to fledging too. What makes the difference for survival versus death for these chicks?
"We wanted to understand what was causing 26% of second chicks to die of starvation," Professor Brightsmith remarked. "Scientists often point the finger at a lack of resources in the environment, but if it's about conserving resources, then why do scarlet macaws lay so many eggs?"
To determine whether adequate resources was the problem, Gustavo Martinez, a member of the research team, marked and monitored trees to estimate the amount of fruit — scarlet macaws' main source of food — that could be found in the forests of the Tambopata National Reserve in Peru where the study was conducted.
"Once a month for several years, he would go out and check about 1,300 trees for fruit and flowers," Professor Brightsmith said. "Looking at the data, we can tell that there were times when food scarcity forced macaws to forgo breeding for a season, but we couldn't find any association with chick starvation."
Figure 1. An artificial wooden nest in the Tambopata National Reserve. This is one of the 24 ... [+] artificial nest sites monitored during this study. One adult Scarlet Macaw is sitting on top of the nest and a nearly fledging-aged chick is sitting in the entrance. (Credit: Liz Villanueva Paipay, doi:10.3390/d16110657)
Liz Villanueva PaipayTo watch what the macaws were doing in their nests, Professor Brightsmith, Dr Vigo-Trauco and collaborators installed video cameras in the artificial nest boxes in the Reserve, and collected and analyzed video for ten years.
At the same time, Professor Brightsmith, Dr Vigo-Trauco and collaborators also checked the nests to see which chicks were being fed. This was how they came to the conclusion that some chicks were intentionally being starved.
doi:10.3390/d16110657
doi:10.3390/d16110657"Scarlet macaws have a food sac on their necks called a crop, and in chicks it's very easy to see when it's full of food," Professor Brightsmith explained. "We caught video of female macaws trying to over-feed their oldest chicks while the third chick would be running slowly around the base of the nest with an empty crop, begging for food."
Disturbingly, not only did the female macaws not feed her smallest and hungriest chicks, but she even refused to keep them warm.
"[T]he chicks at that age can't regulate their own body temperature, so they need to be in the nest. We saw that the mother won't even share her body heat with her dying offspring," Professor Brightsmith continued. "As scientists, we try not to do what's called anthropomorphizing — attaching human ideas about morality to animals. But it's hard to watch that and not think of it as parental abuse."
Oddly, the macaw parents were not in agreement about which chicks to neglect to death.
"Sometimes the female macaw will start to bury a chick that she's decided not to feed by kicking nest substrate on top of it," Professor Brightsmith added. "But then the father will come home and unbury the chick and feed it. So, they're not always in agreement, which makes the whole process even more complex."
Losing nearly half of all scarlet macaw chicks hatched every breeding season is a tremendous loss, as well as a waste of energy. Is it possible to save these neglected wild chicks from starvation? Yes. In fact, as part of her doctoral research, Dr Vigo-Trauco developed a program to save these chicks and to give them a chance at life. Basically, the neglected chicks were removed from the nest and raised in captivity for a few weeks before being placed into the nests of macaws that lost their chicks to predation, or that had chicks at a similar developmental stage.
"The key to success is making sure that the chicks all look about the same size," Dr Vigo-Trauco noted. "This encourages the new parents to take care of the foster chick as if it were their own."
Amusingly, the parent macaws were quite surprised when a foster chick mysteriously appeared in their nest box.
"We see them on camera as they land on the nest box, look in, and then look around like they're thinking, 'Did I walk into the wrong house?' It's kind of hilarious," Professor Brightsmith laughed.
"They turn their heads sideways to get a good look at the new chick, think about it for a moment, and then start to feed them."
This conservation program not only successfully saves wild macaw chicks from starvation, but also provides them the opportunity to grow up and live as wild parrots, thanks to their foster parents' care. So far, during three breeding seasons, the foster chick program has already saved the lives of 28 macaw chicks.
Although scarlet macaws are not endangered, many other parrot species are, so this program could be adapted to help endangered parrots increase their numbers.
"Parrots are one of the most endangered groups of birds in the world," Professor Brightsmith observed. "We hope that this program, and the understanding of brood reduction behind it, can assist with the conservation of a broad array of parrot species across the tropics."
Gabriela Vigo-Trauco, Gustavo Martínez-Sovero & Donald J. Brightsmith (2024). Age Difference, Not Food Scarcity or Sibling Interactions, May Drive Brood Reduction in Wild Scarlet Macaws in Southeastern Peru, Diversity 16(11):657doi:10.3390/d16110657
Questions emailed to lead author, Dr Vigo-Trauco, and to senior author, Dr Brightsmith, about this study went unanswered.
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Scarlet Macaw Parents 'play Favorites,' Purposefully Neglecting Younger Chicks
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A Glowing Wonderland Of Flora And Fauna At The Santa Barbara Zoo
ZooLights Returns Bigger and Brighter Than Ever
The 2024 ZooLights at the Santa Barbara ZooPhoto: Ingrid Bostrom
It's not easy to upstage the moving mass of an 18-foot-tall giraffe, or the impossibly vibrant plumage of a scarlet macaw.
But every night for the next two months at the Santa Barbara Zoo, the daytime stars are given a run for their money by the glowing menagerie of ZooLights, now in its third year and bigger and brighter than ever.
Thousands of handcrafted, silk-covered lanterns fill the grounds, from a desert scene down near the pavilion with meerkats, lizards, and peek-a-boo pygmy owl, to a pair of grizzlies catching salmon up by the lawn.
Along the paths and tucked into dark spaces are strobing butterflies, roaring dinosaurs, and creeping vines that culminate in a tower of pitcher plants with mosquitos that must be three feet long. Everywhere you look is something to ogle at.
There are plenty of interactive activities, too ― swings, seesaws, and a stationary bike that lights up LED fireworks will keep active kids occupied. Thirsty adults can enjoy wine and beer for sale at strategic points along the way.
On a recent preview night we barely got past the arch of birds, bugs, and reptiles at the gate. The 2-year-old with us stopped dead in his tracks and stared. And it only got better from there.
We all squealed at the hummingbirds and honeybees, and then spent an inordinate amount of time at the chomping plants. With their big lips and prominent teeth, they looked like the piranha plants from Super Mario Bros., or "Feed me, Seymour," from Little Shop of Horrors, depending on your generation.
Snacks were needed, and available. And thank goodness the play area stays open. Only two of us could cram inside the oversized eggs, but we all slid on cardboard down the turf hill before waving bye to larger-than-life island foxes.
ZooLights is held November 13 to January 12 from 4:40 p.M. To 8:30 p.M. At the Santa Barbara Zoo. Prices range from $21 to $35, depending on peak or non-peak dates. Visit sbzoo.Org. Parking is $11/vehicle, free for S.B. Zoo Members.
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