Birds and Deep Freezes

Jan 10, 2018


Virginia Rail
Credit budgora /

The Truro Christmas Bird Count was held on a frigid January 2, when more than 30 hardy birders braved subzero wind chills to find even hardier birds among the thickets, fields, beaches, and marshes of Wellfleet and Truro. A handful of us were foolish enough to venture out in the deepest predawn cold in search of owls, finding a bare minimum of Northern Saw-whet, Eastern Screech, and Great Horned Owls, barely audible above the wind gusts at times. 


Extra hardy and relatively young birders Keenan Yakola and Ben Lagasse walked the Herring River and wind-blasted Great Island in Wellfleet, racking up at least 15 miles on foot. They were rewarded with 2 Snowy Owls on Great Island, along with a King Eider, 2 Barrow’s Goldeneyes, and the count’s only Saltmarsh Sparrow taking refuge in ice caves in a frozen saltmarsh. Other count highlights included a Snowy Owl standing on the ice of Pilgrim Lake in Truro, and three Virginia Rails that entertained my team as they paddled about in a tiny, improbably unfrozen ditch in the Pamet River marshes in Truro. Normally hard to see birds of dense marsh, these rails were forced out into the open to find liquid water, and were even walking around on someone’s lawn at one point. When the dust had settled at day’s end, the eight teams came together and tallied exactly 100 species, a little below the count’s recent annual average of 105, but a minor victory on a day with freezing winds and very little open fresh water.


So how do birds survive these unholy freezes? We should keep in mind that these are fairly normal temperatures for birds that survive the winters to our north and west – chickadees in Minnesota would consider that last freeze of ours somewhat balmy. The deep freezes have more potential to affect our more recent southern arrivals, like Red-bellied Woodpeckers and Carolina Wrens, as well as birds that require open water, like the Great Blue Herons taking a chance on a New England winter.


While birds have a variety of behavioral and physiological adaptations to surviving the cold, at the most fundamental level, it comes down to calories and water. Small creatures like chickadees and shrews have high metabolic rates and high surface area to volume ratios. This means they need a lot of food to maintain their body temperature - 100 degrees Fahrenheit in chickadees - and they lose heat fast when it’s cold, so they need strategies for surviving those cold nights. In the case of chickadees, they do it by gaining lots of weight during the day, then losing most of it at night. They lower their metabolic rate via a sort of controlled hypothermia, using shivering to keep their body temperature at or above the critical threshold. In the case of shrews, a study in the Europe showed that they actually reduced the size of their brains to save energy in winter. Given some of the winter driving I’ve seen, I suspect many humans also employ this strategy.


While this recent cold snap seems to be over, you can use the next deep freeze to your advantage when it comes to birding. Finding open water will often get you some interesting ducks, like Northern Pintails, Wood Ducks, or Northern Shovelers. Check flowing water like saltmarsh creeks as well as open patches in otherwise frozen ponds and you are likely to find highly concentrated waterfowl assemblages. And open fresh water in an otherwise frozen landscape will also attract whatever songbirds are around, especially if there are nearby dense thickets of fruity shrubs and vines like winterberry and bittersweet. So, now that you’re ready to find birds in a deep freeze, let’s all hope you don’t get the chance to out that into practice again this winter.