I'm willing to bet he's using whatever he gets. It can be a sign of under feeding. My hatchlings are only on rat fuzzies for the first 3 to 5 feeding which happen every 3 days. By a month old they're on pups usually. I keep them in a 3 day feeding schedule until they're getting close to 300 grams and then they get bumped down to a 5 day Schedule until they are 700 to 800.