With a soon to be lack of Vitamin D from the sun, what are some good supplements I can give Ambrose? Also, since he will be in a smaller cage, I want to clean up his diet so he isn't so fat. (Don't tell him I said that!)
Right now he is being fed various amounts of: Grapes, lettuce, wild greens, young sunflower plants, dollarweeds (his favorite), kiwi, yellow squash, fresh corn, black sunflower seeds, & either a walnut, almond, peanut, or pecan (at max 2 times a week). His tastebuds change almost daily it seems, so getting him to eat anything entirely before it goes bad is a miracle! Usually whatever he doesn't eat, Midori, my conure, will eat.

He's pretty fat right now. Here's the most recent picture I have of him.
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Is it healthy for him to be that fat, given the time of year?

Also, I found a vet who will examine pet squirrels - do you think it's a good idea to have him neutered? If so, when and what diet changes will he have to go through?