I believe this would be helpful for game masters to have a quick reference to remember how to rp as animals, monsters and so on. As a GM myself I often find myself having to quickly google the general behaviour of different species. With this addition, as stated, it would personally make it easier to quickly look up while not having to either open a new tab or look it up elsewhere in a panic. :)
I can see a lot of ways that would help. I spend a lot of time creating various monsters and creatures, and it would be nice to have somewhere specific for that kind of detail.
maybe even multiple sections? "typical temperament" (rabits run at sudden noises), "instinctive behaviours" (squirrels hoard and bury nuts and seeds), and "learned abilities/behaviors" (dolphins teach their young to work together to trap fish)?
Since behavior is a bit broad, a new section that's more specifically worded like "temperament" would be great as a non-sapient way to describe a species' general behavior towards others.
I agree with P-47 Thunderbolt. "Behavior" is covered adequately by the other blocks such "Dietary Needs" "Reproduction" and the like.
I think "behavior" is best covered in small pieces under several different categories. Within the Species template, you have sections on Ecology and Habitats, Genetics and Reproduction, Growth, Dietary Needs and Habits, etc. The most common and relevant animal behaviors can be covered under these categories, more effectively and clearly than if they were in their own section.