Now that we're all scared stupid about the threat of deer, I thought I would offer some suggestions on what I've done to address this problem. I don't propose that any of the following are bulletproof solutions, as deer are very erratic creatures. But used in the right combination, they can help stack the deck back in your favor somewhat, I think.....
1) If you ride with any frequency in what is a deer-prone or deer-infested area, you have another great excuse to add some serious lighting to the front of your bike. If your bike looks more like a freight train (or a tractor trailer) coming than a lone flashlight, you are easier to see (and thus, avoid)--and that works (at least to some extent) for deer, too. Also: serious candlepower on the front of your bike makes it easier for you to see motion off to the sides of your bike sooner. For aux driving lights, opt for more of a wide-beam pattern, instead of a "pencil" beam.
2) If you find yourself unable to avoid a deer infested area while on your bike, especially during low-visibility conditions, don't be shy about using your bike's horn(s) intermittently. One could always argue that you could just as easily scare a deer into running in front of you with your horn, but I'd say the odds overall are against this--they should run away from a sound like that, in general.
3) Of course, another tactic in deer-prone areas is to ride at a slower speed than normal, and cover your brakes (especially the front brake). Don't over-ride you bike's headlamps, either (i.e., at night). Probably the very hardest thing here is to try to avoid a panic situation (if you do see deer close by), but lock the brakes up, and (as a result) have a crash anyway from the resulting (high-side or low-side) skid. Thus, plan ahead by practicing your braking skills from higher and higher speeds--until you are comfortable stopping quickly without locking either brake.
4) Trying to keep tailgaters off is important anytime--but is especially so in more deer-prone areas. Nothing is worse than the need to stop very quickly, with "Bubba" basically already able to polish your back fender. When & where possible....slow down, let the tailgaters go on by, and then ride behind them. Using other vehicles as a "front door" is never really a bad idea in this situation or at night, anyway. Of course, if you are behind a cager, be sure and adjust your high beam lights and following distance as appropriate.
5) At the risk of stating the painfully obvious...if you see flashing or twinkling pairs of lights from either side of the road (or a ditch)--assume it is a deer and SLOW DOWN!!! A single deer is usually followed by other deer, so assume there are others behind that one, and adjust your speed and position (or even stop, if the situation justifies it) to give yourself some distance.
6) If you do hit a deer, and you go down--then the only protection you have is of course whatever you are wearing at that time. So....evaluate what your protective gear is...and ask yourself, is it really enough to avoid a serious face or head injury, road rash, etc? Then, upgrade as your finances will permit.
I don't think riding at night is something that one should avoid entirely, as this has its own unique experiences and rewards. Here in the deep south, riding at night is one of the best times to ride during the peak summer months--for obvious reasons. But to properly manage the risks, you & your bike need to be properly equipped for it.
Anyway, I hope some of the above will help others ride more safely where deer and other nocturnal varmints also like to do their thing.....