Scarlet macaw development unfolds through a series of unequal stages. Eggs within the same clutch hatch days apart, younger nestlings can face a much higher risk of dying, and leaving the nest begins weeks of further learning rather than immediate independence. Field research on Ara macao also shows that growth and fledging timing can vary between populations.
Age Gaps Begin Before the Chicks Hatch
Scarlet macaws hatch asynchronously. In studied Costa Rican nests, eggs were laid at intervals of roughly three days. The first chick therefore begins growing before its younger siblings have even hatched. During the first weeks of life, a difference of several days can create a wide gap in body size and development.
This hierarchy has a direct effect on survival. Long-term work in southeastern Peru found that chick starvation was concentrated among later-hatched nestlings. First-hatched chicks were strongly favored, while the risk rose for chicks that entered the brood later.
A study covering 37 nests across 19 breeding seasons found that about 27% of second-hatched chicks starved. Nearly all third- and fourth-hatched chicks in the study failed to survive starvation risk. The researchers found no evidence that sibling aggression or general food availability in the forest explained the pattern. Larger age differences between brood members were associated with a greater chance that the younger chick would starve.
This helps explain why clutch size and the number of young eventually leaving a nest can be very different. A clutch containing several eggs does not mean that the pair will raise the same number of fledglings.
Growth Peaks Before the First Flight
Scarlet macaw chicks begin life almost completely dependent on their parents, but physical growth inside the cavity is rapid. Measurements of 45 wild chicks in southeastern Peru show that different parts of the body develop on different schedules.
The legs develop early. Tarsus growth reached its fastest rate at about 11 days of age and was already close to adult dimensions while the chick was still far from fledging. Bill growth accelerated soon afterward. Wing development continued later into the nestling period and remained unfinished when the birds first left the cavity.
Body mass followed another pattern. The Peruvian chicks reached a measured peak of about 1,082 g at roughly 63 days, then became lighter during the final weeks before fledging. Their average mass shortly before departure was about 916 g. The decline means that the heaviest point in nestling development is not the same as fledging weight.
The same study recorded fledging at an average age of 86.3 days, with individual variation of several days. Research in central Pacific Costa Rica recorded young leaving nests earlier, at about 72–79 days. These field observations show why one fixed fledging age should not be treated as an exact schedule for every wild population.
Fledging also occurs before every structure has reached adult dimensions. Wing feathers continue developing afterward, while flight ability improves through practice outside the nest.
Fledging Opens a Second Developmental Phase
A young scarlet macaw that has left its cavity can fly, but its development is still far from complete. Radiotelemetry work in Costa Rica followed young birds through the weeks after fledging and recorded a gradual transition from dependence to independent movement and feeding.
During the first days outside the nest, fledglings made short flights and remained close to the nesting area. Some were weak flyers and used low perches. In the monitored broods, the young did not return to the nest cavity after fledging.
The parents continued to provide food and close contact. During the first two weeks, the fledglings spent much of their time resting alone and were regularly visited, fed by regurgitation and preened. Both parents took part in this care.
In the closely observed brood, the young remained fully dependent on parental feeding for about eight weeks after fledging. Independent foraging was first recorded during the ninth week. During the same period, the fledglings handled objects more often, improved their flight skills and began spending more time with their sibling and other macaws.
Movement also expanded gradually. Early locations were concentrated near the nest, while later weeks included longer trips between feeding areas and roosts. The post-fledging period therefore includes physical practice, food recognition, movement learning and entry into the wider social group.
Successful Nest Cavities Can Become Repeated Breeding Sites
Scarlet macaws depend on existing tree cavities for nesting rather than excavating an entire nesting chamber themselves. The availability and quality of those cavities can therefore affect whether a pair has a suitable place to reproduce.
Long-term monitoring in lowland Peru found a high rate of reuse after successful nesting. Pairs often returned to cavities that had already produced young, making a productive hollow a resource that can remain important across breeding seasons.
Parental use of the cavity changes as the chicks develop. Observations in Costa Rica found that the amount of time adults spent inside active nests declined as the nestlings grew older. Feeding and protection continue, but older chicks require less constant presence inside the chamber before fledging.
Research in Peru also found that scarlet macaws accepted artificial cavities. Across 12 breeding seasons, natural hollows and monitored artificial nests produced similar reproductive measures. Where suitable natural cavities are limited, this ability to use an alternative nesting structure can directly affect the number of breeding opportunities available to a local population.
Grey parrotPsittacus erithacus
BudgerigarMelopsittacus undulatus