Treetop Sentries

Creature — Squirrel Archer

Reach

When this creature enters, you may forage. If you do, draw a card. (To forage, exile three cards from your graveyard or sacrifice a Food.)

Food is an artifact type. Even though it appears on some creatures, it's never a creature type.
You can't sacrifice a Food to pay multiple costs. For example, you can't sacrifice a Food token to activate its own ability and also to activate Maraleaf Rider's ability.
Whatever you do, don't eat the delicious cards.
If you don't have enough cards in your graveyard or a Food on the battlefield, you can't choose to forage.
Once you announce that you're casting a spell or activating an ability, players can't take actions until you've finished doing so. Notably, opponents can't try to remove cards from your graveyard or Foods you control to stop you from foraging.