Why are the birds still migrating South?

It's March, they should be heading back North. I live in the Midwest and every day for several weeks I watched the grackles, the Blackbirds, and several other species that I cannot readily identify heading south.

And today, I see them splitting up into groups. They've not done this here. Normally, there are Miles and Miles of birds flying over our area, maybe a half mile wide, but miles long. Not today.

Im gonna chalk it up to resting/flying in their sub-groups of a few hundred, vs several thousand.

But I'm not getting why they'reflying south, in March.

Any ornitholigists here that can offer some insight? I'm not an expert, just lived on the migration route all my life. :)

Thanks!