Are feral pigeon populations seasonal?

Last year I know I had more pigeon targets of opportunity at the dairy. I did bust a lot of them but far more were left than what I shot. But this year...so far...I’m only seeing about a dozen of them max flying around the same dairy. This is Virginia if it matters. Just wondering if the numbers are down because it is still winter? Do they fly south for the winter and then come back? 

I hope the population goes back up as they seem more bold and less skittish when there are more of them. 
 
They usually are pressured away by you being after them. You’ll scare away far more then you are able to kill in my experience, depending on your approach/ shot opportunities. 
At a large dairy farm less than a mile from me I was only able to kill a few hundred out of several thousand starlings last year. This year I don’t see half the birds I did last year. They have nothing to do but survive and are good at it. I don’t believe non native birds migrate to speak of.

Good work!
 
In Utah I have observed similar declining numbers? One interesting thing I have experienced multiple times in my pest control venture is, if you don’t want them to leave? Do not let their buddy’s see you pick one up! Especially if they are roosting or at a resting spot. I have watched them panic so bad at times they hit walls, or other structures, total panic and unless there is a nest, they won’t come back or not for a while? I’m guessing they see you as an alpha predator or something? Anyone know if that is the case? Cheers!
 
Pigeons, hoses sparrows and starlings don’t migrate except in the far north. Their behavior changes mightily during breeding and non breeding seasons. In non breeding season they tend to flock up and move around throughout their local range. The easiest time to get them is during breeding season as they have to return to their nests. As you suggested, they do learn to recognize you as a predator, or in my case my car. It’s almost laughable now to see them bolt as I drive my car onto the farms I hunt. I’ve changed up my strategy by hunting from a blind during nesting season and had very good success. But, they are smart and learn quickly, bird brain is a misnomer. 
 
We had/have an outbreak of Pigeon Paramyxovirus in my area. Western South Dakota, for what it is worth.

I occasionally walk my dog in a park that normally has a decent Collard Dove population & it does seem I have seen fewer of them this winter. And of course Murphy's Law means I see them most often in a place I wouldn't dare shoot an air gun. 

Might be worth checking to see if it's a known issue in your area.