What is the correct course of action in this situation?

Your choices 1 (“reduce my speed further”) and 2 (“be ready to brake”) are correct because a wildlife warning sign means you must expect animals at any time, especially near forests, fields, and around dawn/dusk. The key German rule of thumb is: always drive at a speed that lets you stop within the distance you can see to be clear (sichtweite). In a bend with limited visibility, that usually requires slowing down more than you would on a straight, open section.

Reducing speed is the preventive measure: it gives you time to react and shortens your braking distance. Being ready to brake means you increase attention, keep your foot poised, scan the verges/reflector posts area, and avoid distractions so you can react immediately if an animal steps out.

An emergency braking manoeuvre is not the correct “planned” action here. It’s only justified when a collision is otherwise unavoidable and you have checked that hard braking won’t create an even greater danger (for example a vehicle close behind). With wildlife, the correct approach is to anticipate early and slow down, so you don’t end up needing an emergency stop in the first place.