In Australia, the biggest source of trauma in animal crashes are kangaroos (trauma for both for the kangaroos and the humans). The effects of a number of measures that have been found are reproduced in the second figure below. 
As you can see, in this study, the ‘classic measures’ (warning signs, game mirrors, scent signals) do not reduce crashes. Temporary warnings signs and variable message signs may reduce accidents, at least on the short term.
The most effective measure seems to be fencing in combination with speed limit reductions.  

In Europe, clearance of woodlands along roads and feeding moose in winter habitats has been found to reduce crashes as well. A reduction of moose density in winter habitats is likely to have reduced the number of vehicle–moose collisions.  

Reference: Elvik Et. Al, The Handbook of Road Safety Measures, Second Eddition, 2009  

Source: Motorbike Writer, The Age