written by Dave Kwasnick

Do birds change their survival strategy in winter? Yes! They all go to Florida, hike tiny Bermuda shorts up to their necks, play canasta and watch jai alai with friends.

OK, now for the real answer.

Birds do, in fact, change behavior to cope with winter cold (not that we’ve had much of it this season.) But evolution has also bestowed a number of brilliant physiological accoutrements upon them to help ensure survival in frigid temperatures.

Foremost among these are feathers. Made of keratin, same as human hair and fingernails, feathers are far more than components of light-weight airfoils. They’re also amazingly efficient insulators, locking heat against birds’ bodies while locking out wind and moisture. The key is their structure. Call it the original Velcro. Look carefully at the wispy vanes of a feather under a magnifying glass and you’ll see tiny hooklets. When a bird preens itself (or when you pull a feather through your hand) these structures latch onto each other, creating a smooth interlocking surface impenetrable to snow and rain. Additionally, this protects the insulating power of the fluffy down feathers that trap heat closest to birds’ skin.

Ironically, this is why it’s critical for birds to bathe in winter. Grit and plant matter often gets stuck in their outer plumage. This keeps the hooklets from linking together, effectively creating holes that allows precious body heat to escape. Bathing allows birds to remove the grit and increase their feathers’ sealing efficiency. Birds will often take a dip in temperatures well below freezing. But alas, they’re not stupid. If temps take an especially frigid turn, birds will suspend bathing knowing full well that frozen feathers are far worse than a little lost heat.

Of course heat, along with food and water, are probably the most precious commodities in winter. To increase the amount of heat trapped beneath their outer feathers, birds will “puff up.” Doing so creates more micro spaces between body and down feathers to trap warm air, just like when you don your favorite puffer jacket. Plus, cavity nesters such as Mountain and Black-capped Chickadees, Nuthatches, Titmice and Woodpeckers will often crowd into a tree hollow or backyard nesting box at night to share precious body heat. If you do have a nesting box, ensure you clean it out come fall so that it’s an inviting winter refuge. Also make sure the box’s hole faces to the south or southeast so that it get as much warming sunlight as possible. Never face the entrance hole to the west since it’ll capture the prevailing (and chilly) wind currents.

Like wood in a stove, heat is a byproduct of fuel. And for birds that fuel is food. But it’s not just any nutrient that’ll do. In winter, fat is the name of the game. And that’s why nearly all backyard birds, from small to large, prefer black-oil sunflower seed. Wait. Correction: Fresh black-oil sunflower seed. You see, sunflower is an oil-rich seed. That’s the fat content. But if sunflower sits too long, that oil evaporates, giving the desiccated seed meat the diminished nutritional content of a saltine cracker. That’s why you want to give your birds fresh seed. Otherwise, your saving money. But shortchanging birds.

There’s another reason black-oil sunflower seed is important to wintering birds. It’s called “caching.” Many birds, including Clark’s Nutcrackers, Blue, Steller’s and Gray Jays, Mountain and Black-capped Chickadees, Nuthatches, Titmice and Woodpeckers will begin caching (or hiding) seeds during late fall to hedge against the sparsity of winter. Black-oil sunflower in the shell is the perfect nutritional (and durable) vehicle for them to hide behind tree bark, in tree cavities, under roof shingles and wherever else they keep their food stash.

In fact, caching is so important come winter that it alters some bird’s brains. Consider the aforementioned Mountain and Black-capped Chickadees. Starting in fall, they’ll begin to cache as many as 300 seeds per day. Amazingly, they’ll remember where they placed 90% of those seeds for more than 3 months. How? Here’s the cool part. As they begin to hide those seeds, the memory center in their brains grows 30%. That brain center is called the hypothalamus. It’s the same place humans store their memories, too. That enlargement produces a seemingly preternatural recall ability. Yet it happens annually. Come spring, when food is more abundant and Chickadees no longer need the added weight of an enlarged noggin, the hypothalamus returns to its original size.

But as we all know, climate change is inflicting tremendous challenges on all of Earth’s species. Birds especially are taking it on the chin. Still, unlike humans, they and their progenitors have survived for more than 150 million years. So, this isn’t their first apocalyptic rodeo.

Enter the concept of torpor.

Some birds have developed the ability to perform a nightly hibernation when temperatures drop too low. That’s torpor. Essentially, they lower their metabolic rates – in some cases up to 95% – which also reduces both energy expenditure and the need for large amounts of food. Take the Broad-tailed Hummingbird. It travels from its Mexican mountain non-breeding territory in spring to its Rocky Mountain breeding home, where the weather is increasing erratic. Many times, it meets colder than expected temperatures. So the Broad-tailed Hummingbird will cut its body temperature by nearly half come nightfall, dropping from 105F to around 54F. When daytime temperatures warm up, it slowly sheds its torporative state and resumes its normal functions.

Mountain Chickadees do the same thing, though less dramatically. They’ll reduce their body temperatures by 20F for up to 15 hours, which also cuts their fat consumption by about 20%. Unlike Broad-tailed Hummingbirds, which are in an almost death-like state when engaged in torpor, Mountain Chickadees remain awake and can still fly (albeit weakly) to avoid predators.

Interestingly, a study by the Cornell Lab of Ornithology concluded that birds rely on feeders to augment their diets at about the same percentage in winter and summer: no more than 25%. That means the vast amount of their forage still comes from nature, not the helping hands of humans. It’s also the reason birds will never become “addicted” to your feeder in cold temperatures.

Call it a testament to one of nature’s most adaptive – and astounding – creatures.

Dave Kwasnick is an avid birder, writer, nature photographer and, along with his wife Lori, owner of Front Range Birding & Optics in Littleton and Boulder, CO.