As children we were all amused by the March Hare in Lewis Caroll's wonderful book, Alice's Adventures in Wonderland. What he says about hares in March is true, but that's only part of it.
In spring, most animals seem to go crazy. Some are in advanced pregnancy and some are fanatically protective of their young; some are just out of hibernation or torpidity. I was driving across a disused airfield early one March evening when suddenly a sheep appeared from out of the blue and ran head down into the side of the car. The sheep died instantly.
I went to the nearby pub where the landlord identified the owner. I went to tell him what had happened and made a financial settlement satisfactory to both of us. What had happened in that sheep's mind no one can tell. It was not the headlights as it was far from dark. Sadly, the sheep was close to lambing and that was a possible answer. It was a dreadful experience.
Birds have a springtime tendency to fly into car windscreens and lie fluttering on the road usually with a broken neck. Upsetting though it may be, the kindest action is to put the poor creature out of its suffering by hitting it with a stout stick on the head. Never just drive away.
Many wild animals are nocturnal and get attracted by bright light. Badgers, those adorable animals with their black and white faces are especially vulnerable. When the sun goes down, roads retain some of the little heat of the day and animals seek that heat to their peril. Do keep a watchful eye and keep speed down.
However careful you are, accidents do happen and faced with the problem of what to do with an injured animal is a problem as it needs instant action. Never offer food to the animal even if the injury is slight as you will almost certainly offer the wrong food. If you have water aboard (we make a point of always having water and a bowl in the car) give water to the victim. Do not touch the injured animal as if it is returned to the wild the mother or other peer group animals may reject it. Your scent is abhorrent to them. Use a cloth or other material which may smell but not of human scent.
Walking with a friend across a moor we discovered two lambs which had fallen into a stream. In a hedge we found a piece of sacking blown there by wind so that did the trick and the lambs were taken to a adjacent farm and returned to their mother.
Vets are animal lovers and will help with any injured animal but there will be a cost. That's the cost of being a compassionate person.