New Zealand used to be a land dominated by birds before human beings arrive in the 13th century. When human beings started to take over the islands, we hunted the birds for food and bring possums which eat the eggs! Many kinds of birds went into extinct, and they are of many varieties! If we can't see them anymore in the world, maybe we can commemorate them via stamps?
Here's a wiki page with a list: https://w.wiki/428f