Rabbits don't know which way to go, so panic and sit in the line of fire, can be difficult to avoid the silly things.
Most other wildlife, including birds will move, and slowing will not help.
Most wildlife has to compete for food, and when they've found some, others will come and take it away. They get good at moving away at the last moment, to get as much as possible. A car is just another predator/food competitor. A bird will stay put, eating as much as it can, and will move away at the last moment. If you slow down, it just gets longer to eat, and stays longer.
By all means slow a little, but beware following traffic.
Bigger animals of course will make a big dent, but only slow, don't swerve. Most animals will swerve to avoid a predator, so keep straight and let them swerve. Otherwise you have a 50/50 of following them into the ditch.
Pheasants, came from Mauritius, with no natural predators, so do not see cars as such, which is why they happily jump in front.