Sunday, January 7, 2018

Nature: Some birds built to withstand frigid weather

A horned lark seeks seeds/Jim McCormac

January 7, 2018

NATURE
Jim McCormac

The exceptionally frigid weather of late reminds me, as it always does, how tough the feathered crowd is. When the mercury plummets to zero or below, one wonders how birds survive. It’s 1 degree Fahrenheit outside as I write this, and I’d surely not want to overnight out there.
But not only do birds survive Arctic chills, most of them thrive. At least those that linger.
Far fewer species occur in Ohio in winter than any other season. Most birds migrate to warmer, more food-rich climes. Some may only venture a few states southward; others might go all the way to the tropics. They’ll return when days lengthen and food supplies increase.
Half-hardy species can be “fair-weather” migrants, such as blackbirds, turkey vultures and eastern bluebirds. If winter conditions turn brutal, many of them flee south. They may remain in mild winters.
Waterbirds such as ducks, herons and gulls have little choice but to bail out when water turns to ice, as it is now. Still, if any open pockets remain, such as below dams, there will be lingerers. It’s bone-chilling to watch a mallard or ring-billed gull cavorting in freezing water in single-digit temps, acting as if it’s on a Florida beach.
Birds have a physiological mechanism that helps them cope with cold: a specialized circulatory system called the rete mirabile, a Latin term meaning “wonderful net.” Dense meshlike arteries and veins in the feet and legs efficiently circulate warm blood, thus preventing freezing.
Birds’ feathers are magical insulators. Imagine wearing a heated sleeping bag. A dense layer of down feathers traps and retains body heat. Overlapping the down, like shingles, are various contour feathers. These further prevent heat loss, shield against icy gusts and repel water.
Behavior helps, too. Birds will often alternate tucking their legs into dense feathers when at rest, an effective warming tactic. They’ll fluff their down to elephantine proportions, becoming fat, toasty butterballs.
Of course, food is the fuel that stokes avian fires and gives them the energy to combat frigid winter weather. American robins, European starlings and cedar waxwings form nomadic flocks, moving between fruit trees. Seed-eaters often become more plentiful at backyard feeders during cold snaps. Blue jays, nuthatches and red-headed woodpeckers tap into caches of seeds they hid in the fall. Open pockets of water can be packed with gulls and ducks seeking fish and aquatic plants.

Perhaps the most amazing of our wintering songbirds is the golden-crowned kinglet. One of these Lilliputs is just 4 inches long and weighs the same as a quarter. An Ohio winter is their tropical vacation. Most kinglets breed in the broad swath of coniferous forest spanning Canada and the northern United States.
Remarkably, kinglets are almost entirely insectivorous. They are adept at locating insects and their larvae, especially caterpillars. Yes, caterpillars. A number of species of inchworms overwinter on branches, freezing solid, and emerging from their cryogenic state when temperatures warm. Many fall prey to sharp-eyed kinglets.
To help survive long, cold winter nights, kinglets sometimes huddle together under snow-capped conifer needles, creating their own microclimate.
Perhaps toughest of all songbirds is the horned lark. These birds frequent wide-open agricultural wastelands, where they forage for seeds. Howling winds, polar temperatures and snow cover do not deter them. Come nightfall and plunging mercury, larks huddle in earthen divots, or even become covered with snow, which helps insulate them.
Cold as you may be watching them, don’t worry much about the birds. They’ve been dealing with frosty winters far longer than we have.
Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.
A tiny golden-crowned kinglet foraging in single-digit temperatures/Jim McCormac

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