Here's a link that will take you to 35 of them. OpenLibrary is another source. Even Bill Gates has funded some digital textbooks for free.

Really, you just have to Google "free PDF [subject of interest] textbook download" and you can find just about anything you're interested in now. Even veterinary textbooks and nuclear physics.

https://www.infobooks.org/free-pdf-books/biology/ecology/

Haha. Yeah, all this nonsensical bickering over Black Ariel is hurting my soul because it's so blisteringly idiotic. It's right up there with which franchise is more realistic: Star Wars or Star Trek. Or who's the GOAT arguments. Give me a break and spare me the unnecessary drama.

I can't believe I forgot a special call out for Penguins. Penguins hunt in open water so they have that color patterning dichotomy too. Penguins are horizontal when flying through the water, which makes them dark on top and light on the bottom too.

Nonetheless, I hope you'll keep a weather eye out for those killer whales and leopard seals. ;)