Trout Pod Up In Winter Video

Finally reset my PW so I can post and not just read on here...
I was out fishing with some pals last month for trout, there was a lot of snow on the ground, and it was cold. We moved around, hits lot of water, and dabbled in the whiskey until we finally found a great hole with great fish...lots of them. I'd hooked up with quite a few so I decided to put my camera under water. I didn't watch the video until I was back that night but was blown away, there were ALOT of bows hanging out together in this hole, and you could not see then from above (see video below). I typically always find the trout pod up together in the winter (when I hook one I make sure to fish the water well...), but always curious WHY they pod up like this. I haven't bothered to search the forum for an answer, so I'll do that when I have some time, but either way thought you'd appreciate the video below:

I think they pod up because their habitat needs merge at that time, and there's only so many places that scratch that itch just the right way.