by seeing their adults of course but most of them are natural instincts with animals... no one needs to tech fish how to swim they know what they want and they naturally do it.
What kind of dumb question is that it is not a dumb question! i don't know how to whistle either! this is how you wistle you poke your tongue out of your mouth and blow really hardbite your tongue...
Nests can tell us a lot. You can learn the species. You can learn how long ago the bird left the nest. And various other facts. You can learn the species because some birds have unique nests. Osprey...