A 1.5 year old buck has been run off by the other bucks and isn't tolerated by the does. He is alone and a grunt call makes him think a new buddy may be near. A doe bleat makes him think he might get lucky. They are very call susceptible. Not so with a fawn(we call them yearlings). Does can be super smart. I have not seen any super wary 1.5 year old bucks. I think that is why they account for such a big percent of the yearly harvest.