I believe this is from an Owl.
There's an assortment from Jan thru March 2014 on Flickr, here: https://www.flickr.com/photos/rockyraybell/sets/72157643156099815/ . I see this and they turn up in photos pretty much year round, though this month has been heavy. Single digit temperatures and light snow are not an issue for it. I'm guessing a great horned owl, and I think this may be a mix of pellets, gas, and other presents it drops and expels here and there. An alternative to the swamp gas thing. Maybe some kind of chemical reaction gives off a brief flash. That's all I see is a flash, except for the balls of white light that are there just long enough for me to look and think, what's that. Then gone. I'm open to other possibilities, but keep in mind that whatever it is it can tolerate temps in the zero range, maybe colder.