How do birds stay warm?

Feeding high-energy suet helps birds like this Bewick's wren survive the cold. Photo by J.J. Meyer

In case you missed my column in the Orange County Register today, here is:

Orange County may be experiencing a streak of beautiful weather by day, but those clear skies can make for nippy temperatures at night.  Unfortunately, birds can’t reach for a hot toddy or throw on a blanket to keep them warm.

To survive the cold, birds must rely on a variety of physiological and behavioral adaptations to survive.

            “Like humans and mammals, birds are warm-blooded and must maintain a constant body temperature between 104 and 108 degrees,” said Trude Hurd, Education Project Director for Sea and Sage Audubon. Scientists refer to the ability to regulate body temperature as thermoregulation, she said.

“When the environment is too cold, birds fluff their feathers to trap a layer of warm air against their body,” Hurd said.  “It’s common to see mourning doves sitting on a wire all puffed up when it’s cold outside.”

The concept is similar to how humans keep warm by snuggling under a pile of blankets.  It may be cold when we first get into bed, but soon the air underneath the blankets warms up from our body heat.

“Some birds also tuck their legs and feet into their breast feathers to keep heat from escaping,” she said.

Birds also have a mechanism to generate body heat that’s similar to shivering.  But it’s not the same trembling motion seen when humans are cold. Instead, birds use muscle contractions to create body heat without visible shaking.

When temperatures drop, birds need to eat more to generate heat, Hurd said. Extra calories stoke their metabolic rate and add to their fat reserves to insulate them against the cold. Many birds such as chickadees, nuthatches, titmice, woodpeckers and scrub jays plan ahead by caching seeds and nuts for the winter.

In spring and summer, insects and spiders are an abundant source of nutrition for many songbirds. But in fall and winter, many avian species shift their diets to fruits and seeds to survive.

            “Insect-eating birds have a difficult time,” Hurd said. “In winter, many types insects have either died off or become dormant.”

            Hurd offers live mealworms to a pair of black phoebes that frequent her yard. The small black and white birds are flycatchers, which rely on flying insects for food.

            Despite our cold nights, local non-migratory hummingbirds are already nesting.  Hummingbirds rely on fruit flies and small spiders for protein to feed their young, but they also need a source of nectar.   

            “Fortunately, many California native plants are still blooming,” she said. California fuchsia and various sage plants provide nectar for hummingbirds this time of year.  “That’s why planting natives is so important.”

            A simple way to help local songbirds survive the cold is to fill hanging bird feeders with black oil sunflower seeds, which are nutritious and high in fat. Woodpeckers, crows, ravens and scrub jays will appreciate high-energy nuts and suet cakes. 

Happy Birding!

J.J.