I know some of my Geese love to eat earthworms if they’re lucky enough to find one. Geese are grazers, their entire physiology supports it and I’ve never heard of a goose getting their protein by choice from other vertebrates, but they're each individuals who like different things and it...
Just reading through this and I thought I’d offer a tip because I’ve got picky eaters.
If he won’t touch his crumbles, try putting it in a bowl with a lot of water, make him a crumble soup, he’ll probably want to play in it so he may make a mess, but it’s how he’ll get used to the taste.
Also...