Every hive is different. Certainly much can be gained by studting the entrance. Once you see something different, or questionable, it is up to you the beekeeper, to open up the hive and take a look. It may be something, or it may not.
I will say, that even here in the north, the bees are favoring collecting pollen. A few days back, I put some syrup out. After awhile, I also put some dry substitute out, and the bees went from the syrup to the pollen sub almost immediately.