So, you're tracking down a confusing fall warbler or other difficult bird. You're taking looks through the bins and simultaneously consulting your favorite bird book. As you switch back and forth from book to binoculars, you awkwardly clamp the book, opened to the right page, under your arm or between your legs. You know from experience that traditional bookmarks made from pieces of paper don't work since they inevitably blow away in the wind. Besides, they block the view of text or pictures in the book.
Here's a handy tip: Get a piece of thin ribbon about three times as long as your book is tall. Fold it in half, and glue the folded part into the spine if it's a hardcover book or between the cover and first or last page near the spine if it's a softcover.
Then reap the praise of all your fellow birders as they notice what a great idea you had! If they remark that it looks like a bible, you can remark, "Well, it is my birding bible!"