I mean you don’t want to give them a ton everyday. But mixing garlic in bird feed weekly or bi-weekly has way more benefits than cons. I give mine extra hot spice with garlic in it to keep out the rodents because birds can’t taste the flavor and it prevents parasites and boosts their immune system 😄
Garlic and onions are toxic to just about all mammals except humans, but not to birds. They didn’t need to be toxic to birds because birds don’t dig them up and try to eat them.
Peppers don’t burn birds because they were designed not to. Evolution was aiming to make the peppers only edible by birds so mammals would leave them alone and birds would eat them to spread the seeds.