When I can't go to the zoo or to Africa to sketch I will watch endless videos and read books about the subject. One of the ways that I found works nicely for me is to position my drawing table where I can also view my computer. If I have photos saved there or a video running I can sketch as I use those things for reference.
I keep the manuscript handy as well and might make changes in my overall idea for either the illustrations or the story I am writing.
