Hatchling (naked and may be blind)
Limited hand-feeding knowledge is available for birds at this age, however, it's suspected they can be fed the same way as any other finch type bird, very carefully with a more experienced rehabber's help if necessary. One suggested diet for these birds is Kaytee Exact with a little papaya (80% Kaytee to 20% papaya) for all stages of hand feeding. One rehabber reports that Nutri-Start fed to older babies resulted in a failure to thrive. There seems to be nutrients in both the Kaytee and papaya that this bird needs to grow properly.
Nestling (pinfeathers or feathers, but not flying yet and won't really for a LONG time)
Feed VERY carefully during all stages of hand feeding. Give small amounts at a time (3-4 cc) and go right to left into the mouth as you are facing the bird. This bird is tricky to feed because you also have to get the syringe fairly deep down the throat, almost shoving it, or the baby will hack and cough on formula. Parents have been observed to literally SHOVE food down their babies’ throats. 80% DRIED formula and 20% papaya and then warm water added to applesauce consistency. Add two to three mealworms (preferably ones who've recently shed their skins - they are white) and pea size bits of soft tofu or boiled egg for additional protein supplement. Protein is important at this stage for proper feather growth. Pinfeather babies should be fed every half hour to 45 minutes. Feathered babies should be fed every 45 minutes to one and a half hours, as they get older. Nestlings take a very long time to get serious about flying that you might think something is wrong with the bird's wings. Just be patient and they will eventually start flying. Cardinals will want to wean before they want to fly due to physiological changes with the beak. When you are feeding every hour or so, start offering pieces of papaya, tofu, cockatiel diet, and mealworms for the bird to pick at.
Fledgling/Adolescent (FINALLY flying)
Look for consistent flight and a fairly large baby. Feed the adult diet.
These birds are not true finches and are basically omnivorous. The crop is located down in the "belly" area but is not the same as the other birds in this category. They've been observed to eat practically everything. A good diet for adolescents (birds no longer wanting or needing to be handfed) and adults is a high-quality cockatiel seed mix (Kaytee Fiesta is very good). They will also do okay on wild birdseed but develop better plumage with the variety cockatiel diet has. Papaya and banana can be given to supplement the diet and are enjoyed. Four to five mealworms, tofu, and chopped, boiled egg can be given in smaller quantities.
(Adapted from material provided by Merri Keeton)