The Weekly Chirp: Wondrous waterfowl

With temperatures finally dropping down to the low 30s last week, it appears the transition from autumn to winter is upon us (but shout out to climate change for those extra couple of warm weeks). Cold winds and gloomy, gray skies provoke several behavioral responses in humans, but mainly a marked shift from light fleeces and windbreakers to heavy winter jackets. This is how we’ve “adapted” to live in freezing cold climates — when one layer becomes insufficient, simply throw on another. But life isn’t this simple for birds inhabiting New England and other temperate regions with significant winters. Instead of throwing on jackets (What if they did, though? That would be the cutest thing EVER), birds have developed a series of adaptations to cope with low temperatures and minimize heat loss during the winter months.

The rigid but nutrient-rich waters of the Gulf of Maine host a diverse collection of “sea ducks,” composed of eiders, scoters, alcids, grebes, loons and exuberant specialties like the sexy harlequin duck. These ducks inhabit the northern coasts of Canada and in the Arctic during the summer breeding season, but migrate south in the fall to spend their winters on the relatively warmer Gulf of Maine. Upon observing rafts of sea ducks floating out in the middle of the freezing winter seas, the number one question that immediately arises in a birder’s head is: how the heck do they stay warm? Specialized feathers and oil glands may cover and waterproof their bodies, but their feet are both unprotected and underwater for the entirety of the winter — how come they don’t freeze off?

The answer lies in a concept biologists have termed countercurrent exchange. Unlike in humans, the arteries (carrying blood toward a part of the body) and the veins (carrying blood away from a part of the body) in a duck’s leg are adjacent to each other, facilitating heat exchange from the warm blood of the arteries to the cold blood of the veins. This results in slightly colder arterial blood but also slightly warmer venous blood, which maintains a constant temperature in the duck’s feet while providing tissues with sufficient oxygen and nutrients to continue functioning and not freeze. These countercurrent exchange systems are present in various taxonomic groups of sea-dwelling organisms, from sea ducks, gulls and other pelagic birds, to many species of fish like the yellowfin tuna.

While as humans we may not share this complex heat exchange system, we do possess a couple of physiological responses that aid us in coping with cold climates. The two primary examples are shivering and vasoconstriction. The former increases short-term muscle activity and results in heat production, while the latter lowers the amount of blood traveling to our peripheries and focuses on increasing our core temperature (that’s why your fingers and toes always get cold first). Alternatively, you can find a snuggle buddy (or perhaps multiple) — they’ll warm you up even more. It’s no countercurrent exchange, but hey, we can’t all be birds.

A warm embrace,

Henry