Channelknight Fadran

wooooah even google doesn’t know 

Ok I did some digging and Cole Porter wrote a song called Let's Do It. And in the lyrics it says, 'And that's why birds do it, bees do it / Even educated fleas do it / Let's do it, let's fall in love.' And in the late 1920's it became a widely used euphemism for human reproduction, but let's be honest it's all mammalian reproduction.

Source:https://grammarist.com/phrase/the-birds-and-the-bees/#:~:text=In%201928%2C%20Cole%20Porter%20wrote,reproduction%2C%20was%20in%20common%20usage.

https://www.theguardian.com/notesandqueries/query/0,5753,-59084,00.html

Because why not have a euphemism for mammalian reproduction that mentions two different types of creatures, neither of which are mammals

This makes total sense!