Golden-crowned kinglet (Josiah Lavender)

By Terry W. Johnson

In December, I stepped outside on a frigid morning and was greeted with a blast of a 22-degree Fahrenheit air. I immediately zipped up my coat. I had ventured outside to see if I could see and or hear some of my backyard bird neighbors.

Within less than a minute I heard the cheerful call of a Carolina wren. It was interrupted with the Oh, Canada, Canada, Canada song of a white-throated sparrow. I then pulled out my cell phone and turned on my Merlin bird identification app. And in only a few more minutes, it detected three more species of birds. The calls were highlighted by the high-pitched teez, teez, teez of a golden-crowned kinglet.

Golden-crowneds aren’t fazed by frigid weather. In fact, these small birds can survive temperatures that reach as low as negative 40 degrees Fahrenheit. And here I was shivering in a temperature that was, comparatively, balmy. Which raised the question, how do golden-crowned kinglets do it?

While biologists will readily admit we do know a lot about this bird’s ability to withstand cold temperatures, there is much more we have not deciphered. Here are some of the fascinating facts that research has revealed during the past few decades. 

First, the golden-crowned kinglet’s body temperature runs at 111 degrees Fahrenheit, much higher than that of humans and even most other birds (the latter are about 104 degrees). These petite birds also reduce their loss of body heat by roosting in small groups on cold winter nights. Similar-sized birds are able to reduce their loss of body heat by 37 percent when three of them roost together. 

In the case of the golden-crowned kinglet, not too long ago some biologists shared the opinion that the kinglets roosted in old bird and squirrel nests. Then an intrepid biologist, Dr. Bernd Heinrich, was in the right place at the right time and watched four of the tiny birds roost together on a spruce branch. The birds huddled together with their tail feathers pointing outward. 

The bodies of golden-crowned kinglets are covered in a thick layer of down, essentially forming a half-inch layer of feathers as insulation. The bird's very short legs also help reduce heat loss. On top of that, a single stiff feather covers each nare (commonly referred to as nostrils), apparently further reducing heat loss.

Obviously, fuel is needed to stoke the bird’s internal fires that enable it to survive the unforgiving cold of a winter night. Heinrich, a professor emeritus at the University of Vermont, spent years researching how golden-crowned kinglets should, by all appearances, exhaust their stored food many times over each night just to stay alive during extreme cold. 

This would be especially true when you consider that 90 percent of the bird’s diet consists of insects. While not a problem during warmer months, when kinglets scour the tips of conifer tree branches, the base of pine needles and the underside of leaves to find an abundance of insect eggs, tiny caterpillars, beetles and spiders, and even moths and butterflies. 

But during winter, when insects are scarcer, the fact that these birds can find enough food is almost incomprehensible. For example, in one study researchers determined that when the temperature dips to negative 29 degrees, golden-crowned kinglets burn up to 13 calories a minute just to stay warm. Yet in spite of this demand, one researcher found that the weight of a golden-crowned went from .2 grams at 8 a.m. to .6 grams by 5 p.m. The bird actually gained weight. This helps explain why these tiny creatures rarely pause more than 2 seconds in their search for food, somehow finding and eating enough to keep going.  

At that time, the popular notion was that during winter the golden-crowned’s primary source of food was springtails, or snow fleas. Heinrich could not believe this was the case, but he had no idea what the birds might be eating. If his hunch was correct, he had to find the kinglet’s winter food. Even after he retired, Heinrich steadfastly continued trying to solve this mystery. 

Finally, in 1995, after years of research in the forests of Maine, he and his student assistants made the startling discovery that the primary winter food of golden-crowned kinglets is overwintering Geometrid moth caterpillars. We call these caterpillars inchworms.  

The scientist then had to identify what species of moth caterpillars the birds were eating – no easy task considering there are roughly 1,400 species of Geometrid moths. It turned out the targeted moth was the one-spotted variant (Hypagyrtis unipunctata), a species whose range extends from Nova Scotia to Florida. Fortunately for the kinglets, these insects are abundant because the one-spotted variant has several hosts, including oaks, alders, willows, birches and balsam fir.

The caterpillars also hide in plain sight. Once a tree’s growing season ends, these inchworms perch on a branch and transform into pupae that look amazingly like a twig. But the golden-crown kinglet is not fooled by this camouflage and gobbles up as many of these tiny “sticks” as they can find.

I must confess I have never seen one of these wintering caterpillars. However, finding one this winter is one of my New Year’s resolutions.

Chances are you may have never seen a golden-crowned kinglet in your yard. One reason for this is these beautiful birds rarely visit seed or even suet feeders. Also, most of us either overlook or, maybe because of hearing loss, cannot hear the kinglet’s high-pitched call. The free Merlin app can help solve this problem. If the app detects a golden-crowned, you can then search for a bird you know is there.

Look for golden-crowneds hunting in the tops of trees, in brush piles and even thick shrubs. If you still cannot find one, try pishing for kinglets. Just purse your lips and make a kissing or hissing sound (more information can be found on the Audubon website)

If you prove to be a good pisher, you will be amazed how many birds such as ruby- and golden-crowned kinglets, downy woodpeckers, Carolina chickadee and others will fly in to investigate the odd sound.

Here’s another tip: If you find a mixed flock of chickadees, titmice and other small birds foraging together, look closely at each of them. Sometimes, golden- and ruby-crowned kinglets will be hunting with them.

As for me, on the cold morning I described at the beginning of this column, I failed to find a golden-crowned. Still, I had a great time. I must admit, however, that when I returned to the warmth of my home, I was feeling a little wimpy: The bit of cold weather that chilled me to the bone wouldn’t have bothered the golden-crowned kinglet.

Terry W. Johnson is a retired Georgia DNR program manager and executive director of The Environmental Resources Network, or TERN, the friends group of DNR’s Wildlife Conservation Section. Check out past columns, his Backyard Wildlife Connection blog and his book “A Journey of Discovery: Monroe County Outdoors.” Permission is required to reprint a column.