A fabulous look at the types of animals present in Beowulf, when those animals appear, and how those animals were relevent to the Anglo-Saxons can be found here
As you read (you can skim through the very first few parts to get the the important stuff), you will see mention of many types of "real" animals and descriptions of when they are found within the epic, Beowulf's (or his men's) response to the animals, and so on.
Also, keep in my that the Anglo-Saxons are pagans who think differently about animals than you might expect. Perhaps looking into the history of Anglo-Saxons might be useful to you, too. Here's a good place to start that journey:
Don't forget to take advantage of eNotes in-depth study guides when you start discussing the monsters. You'd be surprised at what those monsters might actually represent. Get a head start on that here:
Good luck with it!