Birds build snow tunnels for fun

Whether it's making snow angels or building a snow man, most of us love playing in a winter wonderland - and it turns out some birds do too. It usually starts with one bird that burrows in the snow, creating tunnels. Another joins in, then a few more, until the entire group is doing it, leaving behind a maze of burrows and furrows. Bernd Heinrich, professor emeritus at the University of Vermont, studied the peculiar behaviour in Western Maine.
He observed a flock of about 150 redpolls (Carduelis flammea) making at least 252 cavities and short tunnels between November 2012 and February 2013, and has just published his findings (Northeastern Naturalist, doi.org/xvj).
He didn't see any evidence that redpolls are seeking food in the snow and there wasn't any vegetation near the tunnels. The birds were also unlikely to be bathing, as they were very clean, and they didn't appear to be taking shelter – so were they just having fun?
 "Play is defined as behaviour with no immediate function, so in that sense, yes, it is 'just' play," Heinrich says.