brand new way too skinny pionus

[clicerhelp]

Hello board,

I've owned an african grey before. she would eat anything and everything. i never had a problem feeding her and never gave AMOUNT oHerf food a second thought (only nutrician). I now have 2 brand new pionus. i know nothing about pionus parrots (except that I've read some of the research on wild pionus diet in the wild). The 2 birds are on their 3rd day in my home. One of the birds is dangerously thin. The vet says I need to fatten him/her up.

The bird, Ricco, has taken almonds from me, but will only eat about half an almond then tosses the rest. The same for Brazil nuts, hazelnuts. (S)he took a walnut but only took one bite then tossed the rest. won't eat pecans.

how much (quantity) should a pionus consume each day? what about in order to gain weight? Should I try to feed very high fat foods?

Need guidance,
Val