SpasmsOfMating
Tourist
These books are available on the archive.org online library. They can be borrowed an unlimited amount of times (you need to make a free account). Note that there's a limit to how many people can borrow at the same time (probably just one), so you may need to come back later (I've never had the issue, but I guess this thread itself might cause it while it's new).
Note for the privacy-conscious: especially while this thread is new, borrowing the books might in theory be indirect evidence that you visit this forum, so you might consider e.g. registering on archive.org with a throwaway e-mail instead of your regular one (assuming you do the same for this forum).
"The Sexual Connection: mating the wild way" by John Sparks: https://archive.org/details/sexualconnection0000spar_x1p6/page/18/mode/2up
This has some very informative, well-researched and often juicy details about a great variety of animal mating and genitals, written in a very engaging and sexy style, and making a lot of connections with human sexuality. It does mention at one point the common misinformation that most female animals don't have orgasm (I'm not actually aware of any conclusive evidence for any species that there is no female orgasm, and there's been minimal scientific study into this), but otherwise it very much depicts animals as enjoying sex much like people do. Also contains non-judgemental discussion of zoophilia (another factual error is reporting the Catherine the Great horse myth as fact).
"How They Do It" by Robert A Wallace: https://archive.org/details/howtheydoit00wall/page/n5/mode/2up
Contains chapters for various species, again with very vivid and juicy details for the sex act in various animals.
Note for the privacy-conscious: especially while this thread is new, borrowing the books might in theory be indirect evidence that you visit this forum, so you might consider e.g. registering on archive.org with a throwaway e-mail instead of your regular one (assuming you do the same for this forum).
"The Sexual Connection: mating the wild way" by John Sparks: https://archive.org/details/sexualconnection0000spar_x1p6/page/18/mode/2up
This has some very informative, well-researched and often juicy details about a great variety of animal mating and genitals, written in a very engaging and sexy style, and making a lot of connections with human sexuality. It does mention at one point the common misinformation that most female animals don't have orgasm (I'm not actually aware of any conclusive evidence for any species that there is no female orgasm, and there's been minimal scientific study into this), but otherwise it very much depicts animals as enjoying sex much like people do. Also contains non-judgemental discussion of zoophilia (another factual error is reporting the Catherine the Great horse myth as fact).
"How They Do It" by Robert A Wallace: https://archive.org/details/howtheydoit00wall/page/n5/mode/2up
Contains chapters for various species, again with very vivid and juicy details for the sex act in various animals.