Kinglets: tiny and fascinating

It was while researching gardening for butterflies and moths recently that I was reminded of the story of the Golden-crowned Kinglet, Regulus (little king) satrapa (governor), an olive-grey bird named for its brightly coloured crest - orange in the male, yellow in the female.

What a fascinating little bird it is!

The first amazing thing about the kinglet is that it’s so tiny, our smallest songbird. It weighs in at 5 grams - not much more than a quarter - and is half the body size of a chickadee. Which leads us to the second amazing thing: it eats only insects, but unlike most insectivorous birds it does not migrate - so how does it live through our punishing winters?

The third amazing thing is that even given an adequate winter insect diet, it seems physically impossible that it would be able to eat enough to carry it through a long winter night. That’s because its very small size means that the ratio of exterior exposure to heat loss versus inner body mass to store heat is higher than that of other birds.

In his bestselling book Winter World, naturalist Bernd Heinrich calculated that just to stay alive, at rest, a goldcrown would have to use up all its food reserves several times every night, theoretically dying of starvation several times over. I’d read Winter World many years ago but hadn’t realized the importance of Heinrich’s research on kinglets until Gardening for Moths by Jim McCormac and Chelsea Gottfried took me back to him with a reference to his “tireless work” in revealing how kinglets subsist on inchworms, the caterpillars of a moth in the Geometrid family, “to fuel their bonfire metabolisms.”

Inchworms, by the way, are so named because unlike other caterpillars, they lack a full set of legs, relying on a set at the back and another on the front to pull them forward, inch by inch.

Heinrich’s work spanned several years and included hours of painstaking observation in the field.
Golden-Crowned Kinglet
Robert Codd photo

As he recounts in Winter World, he soon discarded a then widely held theory that in winter kinglets feed on springtails (snow fleas) but he was no closer to answering “how do these goldcrowns manage to find up to three times their bodyweight of food each short winter day?”

He had no doubt that they needed a high-energy diet, because they have an exceptionally high body temperature of 43 to 44 C, some 3 C higher than that of most birds, and 6 to 7 C higher than that of a healthy human.

Solving the mystery would be difficult, but important, he writes. “Knowing what a bird eats is fundamental if not essential to understanding the mysteries of its survival.” So, “with regrets,” he shot several kinglets and examined their stomach contents. To his astonishment, he found them filled to capacity with the partially digested remains of dozens of inchworm caterpillars.

“I would not have been more surprised if I’d have found earthworms.” The caterpillars of most Geometrid species are known to overwinter as pupae, safe from frost under snow or leaf litter. But that was not where kinglets had been seen to forage. Their hyperactive lives play out in trees, and “nobody,” Heinrich noted, “had reported seeing caterpillars on trees in the northern winter before.”

This was January 1995, and Heinrich and his students sallied forth in the minus 30 F Maine winter to bang on trees. Inchworm caterpillars matching those found in the kinglets’ stomachs fell onto the snow along with woody debris and other overwintering insects. That was a step forward in solving the mystery. But the unexpected fact of these caterpillars existing on open branches and being winter food for kinglets was not enough; he needed to identify them – there are 1,400 species in the Geometridae family in North America alone.

An entomological expert was unable to find a match and suggested rearing out the caterpillars for identification as adults. So, the following year, Heinrich tried to do so but the unfrozen and feeding cats got predated by a spider. In the next couple of years a series of mishaps befell two further generations. In 2000, he finally reared adult moths that were identified as the well-known One-spotted Variant (Hypagyrtis unipunctata).

It had not previously been known – except to kinglets - that the caterpillars of this particular species of moth departed from the norm for their genus by overwintering flattened on branches, going through freeze-thaw cycles with no apparent harm.

Winter World came out in 2003, but for Heinrich, another mystery remained. Where did the kinglets shelter during the winter nights? He would follow the groups of up to 6 kinglets that seemed to stay together - but at dusk, they disappeared, never in the same spot, and he couldn’t find where they went.

He speculated, based on observations that had been made of captive European kinglets, that they might deal with the energy problem of overnighting by huddling as a group, but could not find evidence to support the idea.

Several months after publication, he saw a group disappear into a pine tree at dusk and not come out, their constant calls having ceased. On a hunch, he went back in the dark with a flashlight and looking up, found four birds on a branch, their front ends pressed together, their heads tucked in and their tails sticking out. They were still there when he came back with a camera to document the behaviour for science and also in the early morning. But they never returned to that spot.

He theorizes that a kinglet group forages till the very last moment of the winter day and maintains voice contact with the ceaseless tweets that are a characteristic of these birds’ behaviour. This allows them to huddle wherever some inchworm bonanza may have taken them. The food plant of the One-spotted Variant is extremely diverse, including alders, willows, birches, oaks and balsam fir, so the kinglet has to be adaptable to find its meals, and thus decide on its overnighting perch.

Interesting facts: One goldcrest (the European kinglet) huddled with another reduces heat loss by about 23 per cent, while in trios heat loss is lowered by 37 per cent. And an Austrian biologist studying captive kinglets found they have special calls when they approach their sleeping place. She reported it took 20 minutes for the huddle to form in warm weather, but just five minutes in cold, although mated pairs and siblings can bunch up within seconds. That's so relatable!

The kinglet has ingenious solutions for its many challenges, but as Heinrich memorably says, “like other animals of the north, its life is played out on the anvil of ice and under the hammer of deprivation." As a result, the kinglet’s life span in the wild is short, seldom living beyond a year, as close, to an annual as any bird gets. In captivity, it can live up to 10 years.

The high level of winter mortality is compensated for by a high reproduction rate – 8 to 12 eggs in each of two clutches a year, with the female building the hammock-like nest suspended under the branch of a spruce or other conifer, and thus protected from snow. The male feeds the incubating female and the first brood, and then earns the title of super-dad by bringing in supplies for as many as 24 chicks.

There is another species of kinglet in our area, the Ruby-crowned Kinglet; it resembles the goldcrown, although a little more green in its coloration, with the same habit of constant wing-flicking. It’s a little larger, has a usually concealed red crown patch, no black eye-stripe, but a noticeable white ring around the eye. Originally it was placed in the Regulus genus but the differences were sufficient for it to be assigned its own genus, Corthylio, of which there are three sub-species, with the one we find in Ontario being C. calendula.

Final thought from Heinrich: “To care for the welfare of kinglets, it is necessary to care for the welfare of moths.”

By the way, Heinrich, who has written a series of very readable nature books, as well as many peer-reviewed papers in the fields of botany, insect physiology, zoology, ecology and more, is also a runner. His Wikipedia entry actually devotes more space to his running career than his scientific accomplishments.

This Saturday, local birders are going out on the Christmas Bird Count. I will be looking for kinglets. They are notoriously hard to photograph, says Robert Codd, whose lovely image I have used here. "They're constantly in motion and often high up in the treetops. They are a tiny moving target that favours dense cover and deep shade which adds to the challenge."

I won’t even try for pictures – I’ll be happy just to hear them. Best of the season to all.
Liza Vandermeer
- 11 December 2023 at 07:14pm

Fascinating - thank you. That was very informative.
Mary Jane Price
- 12 December 2023 at 06:08am

I am sending this story to a friend in Australia who will be delighted to read it.
Laurie Wallace
- 12 December 2023 at 01:10pm

Fabulous blog. Thank you.
Margot Edge
- 12 December 2023 at 03:10pm

Thanks Kate. I pass these messages to my Gardener Susan.
Ken Thompson
- 12 December 2023 at 04:03pm

Thank you for your fascinating account! I love learning new things, especially about nature.
- 12 December 2023 at 05:34pm

Wonderful! Love it. Such great detective work, amazing!
Ken MacDonald
- 12 December 2023 at 06:04pm

Heinrich’s autobiography The Snoring Bird is one of my favourite books of all time.
Gaia Seagram
- 12 December 2023 at 07:49pm

Thank you so much for this.
Wilda Mardlin
- 12 December 2023 at 08:27pm

Very interesting blog.
- 13 December 2023 at 09:14am

There is so much we do not know about the natural worrld. Thanks for your curiosity and sharing your findings
Nancy Moysiuk
- 14 December 2023 at 07:08am

I will be looking for kinglets after reading this very interesting research. Another reminder that if we want birds, we don t want to eradicate moths and other insects.
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