Congrats on the new baby. Most of us would rather not support a breeder that sells unweaned chicks because it encourages them to continue doing so. However, since you already have the baby...Some basic pointers would be to make sure to get a gram scale if you don't have one already and weigh the chick at its most empty(usually first thing in the morning). By the looks of it, your baby may actually start to loose weight soon, which is not a terrible thing. A gram scale is just something you'll need for the rest of the bird's life anyway and it helps you monitor for any unexplained weight loss. Most baby birds hit a peak weight which for yellow headed amazons is around 45 days old give or take several days. After that, depending on the chick they will loose 8%-20% of their body weight in preparation for flying. I mention this because some people go out and get a gram scale, and then they get upset when the chick is loosing weight, and they try to get it to eat more, which delays flying and delays weaning which is not good. Also, if your chick starts going through a difficult to feed time very soon, you know why. It is instinctively trying to loose weight. Your job is to make sure it doesn't get unreasonably low and to make sure it isn't a huge uncontrolled loss. It'll also help you make decisions about when to cut out a hand-feeding toward the end of weaning. Later in life, you'll weigh him weekly or so to make sure he hasn't lost weight for no apparent reason which usually indicates time for a vet check even if they aren't showing symptoms.
For now, feed the baby when its hungry. Give it approximately 10% of its body weight per feeding or whatever it will take. If the baby weighs 500g, then 50cc of formula per feeding would be the high end. It looks like at his age, he might be picky and sometimes only want 10cc and that is okay. Offer food whenever the crop looks like it is getting close to empty during the day. At night, let the crop empty completely. If you ever find that the crop is not emptying, then you need a vet check immediately. Like that very day. If you find that the digestion time is slowing down, then you need to make a vet appointment to figure out why. If he has slow crop, don't feed more until all of the old is out of his system.
Right now is also a good time to introduce adult food. I'd offer veggies at least once a day. The chick may or may not eat them. More likely, it will scatter the food all over and smear it around. But, it needs to get used to the taste and feel of food other than formula. You are not weaning the baby now. Actually, it will wean itself if you do everything right. But, you are giving it a chance to learn about food. Warm veggies like cooked soft sweet potato served warm (not hot), cooked rice and beans, thawed mix frozen veggies, plus some of the really fresh food like bits of broccoli and peppers etc. Make sure not to have fresh food in there for him for more than a couple hours as it will become rotten and an infection hazard depending on your climate. Sprouted seeds are also good, but make sure you research sprouting and do your own sprouts. I usually get mine from chinaprairie.com but there are other good places to get sprout mixes from. Offer some pellets for him to crunch up. I usually save regular hard seed for much later in the weaning process.
You can hold him a lot right now. When I had baby amazons of that age, I'd spend a lot of time with them on my lap partially wrapped in a towel and helping them preen the tips off the pin feathers on their heads.
Also, introduce foot toys. Don't give them anything they can swallow that can't be digested (no small beads). But give them things they can roll around and play with. At this age, most of their "toys" should be food items. But, various hard plastic shapes and blocks of wood are good so they get used to them.
Also, let this bird learn to fly. Don't clip his feathers until he has been completely weaned for several weeks. You will have to be very careful about opening and closing doors and windows while the bird is out during this time. Pretty much, always put the bird back in the cage if someone wants to open a door. Keep blinds or curtains at least partially over windows so they learn that they are barriers. Flying helps them feel independent and learn to wean. Clipping makes them feel dependent and makes weaning harder and take longer.
Rain
