The yellow urine would worry me, too. I don't have experience in that area but I have been dealing with some weight loss with my baby Eclectus.
He went from 348g to 340g to 332g over three days. I thankfully am getting some weight back on him. My breeder suggested it could have been a huge bowel movement, combined with the increased activity of going from the small breeder cage to his huge cage, plus ALL the flying.
They are getting a lot more exercise these days. To get my baby eating a bit more, I make his normal formula and then mix in puréed baby food. He loves it so much more. Proper temperature is also very important. He prefers his around 106F-107F and refuses anything less than 104F.
I ordered the Avitech Weight Gain supplement just in case we have any more weight loss. My breeder stressed the importance of daily weight checks each morning, after the big bomb poop but before any food consumption. Especially because my guy is an Ekkie and she said Eclectus are slow and complicated when weaning. I have been playing it by ear and offering plenty of food and variety.
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