Wis,
if you're seeing sign, they are obviously still there. Where I hunt in Missouri, they can change their movement patterns based on a lot of variables, just like ducks (weather, food, water (this is key for our place, there's only a few sources of water over a huge area), length of day, when the rut kicks in). As some of the other guys say, look at the area around your property to see what's changed. 45 acres isn't a "home base" for lots of deer, so you will be affected by those owning property around you quite a bit. Did somebody clear out some timber, or put in a new pond which will prevent deer from following an old path or provide a new food source? On our place, when the neighbor took out some fence rows between a couple of fields, it changed deer movement patterns dramatically. They didn't follow that ditch nearly as often anymore, but another ditch 200 yds away was suddenly a new hot spot! You might need to go scouting some more when it snows (fresh tracks will show up easily) and see what the deer are doing to find the new paths.
Scott