Here, I will link the article it is from. Pamela Clark is well respected with decades of experience with behavior and health of parrots.
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Hunger = Anxiety = Stress
One of the most powerful tools for reducing stress in a young parrot is to feed him warm, soft, nutritious food from a spoon at least once every day. Most hand-reared parrots were never spoon fed when young, since the practice of using a syringe is so popular, but they can learn to enjoy this if the owner is willing to be persistent about offering it on a nightly basis.
The majority of parrots reared for sale by breeders or pet stores are weaned too early, in addition to being deprived of the fledging experience. Early weaning helps to insure an early sale, which maximizes profits. In order to accomplish this, the hand-feeder eliminates feedings according to an arbitrary schedule that will insure that the young parrot is weaned as early as possible. The huge problem with this practice is that hunger and anxiety become closely linked in the minds of baby parrots.
In the wild, no adult parrot wants a chick to be calling for food because this elicits the attention of predators. Babies are fed constantly, rarely ever wanting for food for long. Further, as more breeders allow their pairs to raise their young through weaning and fledging, observations accumulate that prove what we long suspected … that adult parrots will continue to feed their chicks even after they are weaned, apparently to provide reassurance or nurturing if the chick encounters a frightening experience as it becomes more independent. The chick not only does not experience hunger, but it receives feedings even when it only needs to be nurtured or reassured.
Contrast this reality with the common rearing practice of eliminating feedings according to a schedule, which can leave a parrot chick hungry for hours at a time, as he learns to manipulate food in order to feed himself. Further, to compound the anxiety caused by the hunger that he instinctively understands to be unnatural, he also receives no feedings simply for the purpose of reassurance as he meets the challenges of life in a pet store or new home. Thus, hunger and anxiety become inextricably and forever linked in the mind of the parrot.
I believe this is why so many adult parrots do not eat well when feeling anxious. In more consulting cases than I care to count, close questioning reveals a pattern of eating that results in a hungry bird. An anxious young parrot will eat enough to keep himself alive and maintain his weight, but will not eat enough to reach satiety, the point that usually brings a greater sense of relaxation. In many cases, a young bird weaned through deprivation weaning techniques will become food independent, but will have a permanent behavioral disability as a result.
Whenever circumstances cause anxiety for such a bird, he eats less than normal. This results in an edge of hunger, which causes more anxiety, which results in poorer eating habits. This is one reason why anxiety can be so difficult to overcome in parrots, and the key can be to simply feed them a supplemental meal by spoon. Such feeding not only results in a full crop of warm food, which results in a decrease of anxiety and greater relaxation, but it appears to trigger on an instinctive level, a feeling of being nurtured and safe."
https://lafeber.com/pet-birds/stress-reduction-for-parrot-companions/
Also because fledging takes place now, and is huge in the physical development of the body, and mental development learning to fly is critical. As adults they dont have that drive to over come fear of falling, and they have already fallen so much and it hurts, so they have fear , fear to even jump between wide perches, snd difficulty learning to fly well...
https://www.windycityparrot.com/blog/2010/04/13/flight-important-parrots/#ixzz62HloSvKV