Feed them mackerel/sardines for the first few weeks on top of whatever commercial feed you give; aim for four grams of fish protein from the fish per bird for the first few weeks. Take care to read the protein content stated on the tins; not all tinned sardines for example have the same protein content. At 20% protein per drained weight you're looking at roughly one tin for four birds.
I found real food made a major difference in how quickly the birds regained their plumage and overall health.
From this,
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To this in a couple of months.
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