Every writer is different and goes about getting to the elements of their story in a different fashion. Being a fan of the late and great Patrick O'Brian, who was by trade a Naval Historian and consequently wrote a great series of books that I know as the Master and Commander Series. Captain Jack Aubrey and Doctor Maturin were made up and fictional characters but the ships they sailed on, the exploits of what happened between this ship and that ship came right out of the history books. More specifically they came out of Naval Journals, Captains Logs, and British Naval History. There is a paragraph or so at the beginning of each of his books where he explains he couldn't come up with stuff that would overshadow the actual feats of true history. He also explains elements of Naval technology from the sixteen and seventeen hundreds in bits and pieces littered through his work. It is amazing the things you can learn while reading for pleasure, but an author had to put the stuff in there to begin with before you could benefit from the experience.
I enjoy the elements of making up wild stuff in order to take my readers some where they have never been before. I also try not to pass up a chance to blend realism in with the fiction. Let me explain.
In my second novel I needed to come up with an alien race of beings that would be scary, ferocious, and that would breed prolifically. I tried to think of some animal on Earth that if it had become the dominate species and developed into a humanoid type form from its current Earthling cousin that might fit the characteristics I was looking for. I decided upon Alligators! Then I learned everything I could that I thought might be useful in the story to further develop aspects of my new alien race, the Gators.
At the beginning of the book the Gators are over running another alien race which is entirely peaceful. The peaceful group's first option upon discovering this predator was to try and communicate with them. All attempts at communication fail, because the Gators do communicate but at a level below the normal hearing range. This is what I got from researching Gators. Gators communicate with each other using Ultra Low Frequency vibrations. Humans can't hear that range (neither can my peaceful aliens). I was amazed at what I did read about Ultra Low Frequency and the affects it produces in about twenty-two percent of the human population. The effects are most widely seen and experienced today with the proliferation of wind turbine farms going up all over the place. These wind turbines produce Ultra Low Frequency vibrations also.
For those who are affected by these vibrations they get an un-natural, scary feeling, goose bumps, a haunted or evil feeling. Some people have reported seeing hallucinations, seeing something in your peripheral vision that when you turn your head nothing is there. These people are not making this stuff up. Their bodies are picking up or feeling these vibrations, a sound just below our normal hearing range. The hallucinations are caused by the vibrations causing distortions in the people's eyes and their brain interprets the vibrations as images or seeing something. As you turn your head to see more clearly or change the position of your eyes to the vibrations the images just disappear. Alligators can affect people in the same manner. This may lend to why people view Alligators as being as scary as they do. The fact that they will lay in wait for you motionless until they snap, bite and drag you under the water to eat you doesn't hurt their scary factor either.
My point with all this is to say, don't be afraid to do some good old fashioned research about aspects and elements of your stories and incorporate some truth into the fiction. You not only learn something but get a chance to teach your readers something along the way. I love reading because you never know what you might learn along the way. Even in Fictional books!
One of my favorite Authors, James Rollins, in his Sigma Force Series, at the end of his books includes what is real and what is made up. I always enjoy this part immediately after finishing the book. One of his books totally blew me away because everything in the book was based on true stuff!
Mr. Rollins also adds the books he read as research for each particular book. On two occasions I actually read each the books he used for research for that particular novel. It was enlightening in the fact that he could take this piece from here and that piece from there and turn and twist it into the plot line and story that he did to come up with for the novel. It was amazing seeing the raw material and the mental leaps and bounds he had to make to come up with the story that he did. I haven't told my readers what is true and what isn't true in my books but I challenge them to take aspects of the story and look some stuff up on their own and see what's factual and what's fictional. This is just something I enjoy doing behind the scenes and under the radar of the reader. Hopefully it does make the reading more believable, or at least plausible.
Even my first novel "Whisper" the frigate that attacks them was a real ship and disappeared presumably in a storm in the same area and time as the ship disappears in the book. Plausibility, it took me weeks of researching ships and their fates until I came up with just the right ship. Thanks to Wikipedia they even included an artist's picture of the ship.