Early on, I would have agreed that the bird population was low.  Two weeks ago, they lit up and all the birds I wasn't seeing are now running rampant.  Sat in one area the day I shot my first bird and had 5-6 different birds gobbling around me.  I think the population is better than it was last year, but still lower than it was 4 to 5 years earlier.  Regardless....lots of birds to still be had.  
I have noticed that they gobble coming out of roost an then shut up.  Super quiet all day long....until about 5 pm when the gobbles start up.  They gobble and are pretty responsive from 5 pm till they go to roost again.  I have found the afternoon hunts to be the most productive.  I still have one tag to fill so hopefully they stay active for another couple weeks.