~Based on my personal account~
Here in PA, in the past week or so, I have noticed flocks of birds heading north. This is unusual to me, because I tend to feed them birdseed and I
never have to break out bird food during January. These flocks were crows and robins. I figured that either they were just coming home because it's
not as cold as it normally would be. While in the midst of putting out birdseed, the birds reacted really strange, their chirps were intensely loud
and almost distressful sounding(not your normal song like bird chirps) at that same moment I looked up to the left(which would due west)in the sky and
it looked to be two planes almost skywriting?!? making a very definitive white X overhead, I couldn't make out the planes, they looked white with
silver and not flying in a normal pattern one plane looked really close to the other and almost as if they were paired off one flying upwards to the
left and one downwards to the left.
I did some research and found that male robins are more likely to stay put during winter months to have first dibs on setting up breeding territories
come spring.
So I guess what I saw was about 30 male birds just hanging out together(maybe a winter long bachelor party?

)
As for the planes, who knows.
Here is a link to what I was reading..
www.npwrc.usgs.gov...