Yes, in rotation — spinach is nutritious but contains oxalates that bind calcium, which matters especially for egg-laying hens.
What it means for budgies
This is one of the foods we especially recommend for budgies: it plays to what budgies need most — finely chopped vegetables and the occasional millet treat. A budgie portion is tiny — a single bite or a little grated amount is plenty.
The full picture on spinach
Spinach is rich in vitamins A and K, but its oxalic acid binds dietary calcium and can reduce absorption. For most pet parrots an occasional leaf is harmless; for laying hens and birds with calcium issues, frequent spinach is a real concern.
Offer a leaf or two, once or twice a week, washed well.
Rotate with low-oxalate greens like kale and bok choy.
Limit further for laying hens or birds on calcium supplements.