Most likely it is warmer there. Spring is on the way, so they will begin to claim territory and houses.
How many bluebird houses are "in the yard" and how close together?
BlueBars

have 2 boxs in the yard with 1 or 2 more coming.
there at the back two corners of my yard, and my neighbor has two also.

i'm thinking of adding 2 more, one at each corner of my one acre lot.

That sounds like alot of boxes for 1 acre. I live on 3 acres and only managed to squeeze in 4 boxes--I tried 5 and it was just too close. All 4 of my boxes last season had bluebird nestings. Bluebirds are territorial and will spend their time fighting over nesting sites if the boxes are too close. Ideally the boxes should be 100 yards apart, unless they are out of sight of each other. Even then, sometimes the males will fight over hunting territory if they cross paths!
Kathy

the two boxs that I have out are about 125 feet apart.
each year i have had bluebirds in both boxs with no problem.
both raised there young.
the other 2 boxs that i was thinking about will be out of site of the first two.

Hi cuzzx,

It's good to hear that you have had success with Blues nesting in your boxes. I set up 2 new boxes last Fall, very much the same distance and out of sight from each other. My place is about an acre. I now have 4 Bluebird nestboxes here.

I have learned from others who have more than one or two nestboxes on about an acre,that the Blues would use one box and then after the babies fledged will move to another box and use that one. Also, chickadees would use one of the other boxes also. Which wouldn't upset the Blues at all. Nor would this upset me....I like chickadees.

Jean
NW GA