After Steve and I tweaked the bait sites and refilled the barrels and crates, we waited to see if and when the bears returned to the sites. Three days after we were there, Steve went back to check: bam! bears at both sites and no food left.
Other hunters have been seeing the same thing; lots of bears (many of them good sized bears) are already hitting the bait sites hard this season. When Steve and I were up the first time, we noticed that the blackberries and raspberries were not looking good. Without a lot of fun and rain, the berries were small and still very green. The temperature has dropped a few times down to the 40s at night which could kill some of the bear's food source. There are plenty of apples, which we know the bears are eating but those will only be around for so long before they are gone.
This unstable natural food supply means that the bears will need to come to the bait to get those missing calories before they den up.
I hope that I am sitting in a stand when they come in!