I scan the roadside (ditches etc) regularly (once every two - three seconds or so) for wildlife as soon as I am outside the city. In the city, I scan too, but for opening doors, kids, dogs, drunks etc but that´s another issue
Tip A: slow down a little and increase your roadside scanning frequency when approaching dusk or dawn. Animals tend to move at those times.
Tip B: If a deer, a rabbit or whatever comes up from the ditch, slow down without panic braking, hold on to what you got and aim for the BACK end of the animal if you can´t avoid collision. There´s a much bigger chance that the animal keeps moving than stopping, and - in the case of a deer - the rear end is much lighter.
Tip C: Beware of deers - the often come in pairs...
Tip D: if a pheasant pops up from the ditch, it WILL stick its head into your front wheel, decapitate itself and then disintegrate all over you and your bike. The innards stink and are really messy. Get a fire hose and wash the mess off yourself and the bike BEFORE it dries up. Been there, done that
Tip E: If a dove or other large bird pops up as you drive by - DUCK(
)! They are heavy and messy on impact....I found myself with a broken nose, an almost poked out eye and spitting feathers for a long time after such an incident. Not even a full face helmet would have saved me, even if the visors are reasonably stiff
Tip F: In the countryside and in the dark, I tend to choose my line more to the left of where I usually am. This gives me a split-second more time if something pops up from the side.