The Carlisle Mosquito Online

Friday, December 4, 2009

 

“Thanks to Eric Smith (who has way more patience and skill with a camera than I do) for permission to use his excellent photo,” says Alan Ankers.

What?

The Golden-crowned Kinglet (Regulus satrapa) is a tiny bird, smaller than a chickadee, and one of relatively few that are only seen in our area in the winter. You won’t find it at your feeders because, unlike the junco and other winter visitors, it is not a seed-eater.

The kinglet family are the world’s smallest perching birds (only hummingbirds are smaller) and have bright crowns; the genus name regulus means “little king” in Latin. The Golden-crowned Kinglet is about four inches in length and weighs just one-fifth of an ounce, about the same as two pennies. It looks plump, like a little ball of feathers.

Its coloration is generally drab, greenish-gray above and paler underneath with dark wings and tail, but a closer look will show yellow feather edgings on the wings and tail. The head is distinctively marked, with bold black and white stripes on the face. The “golden crown” is a thin, bright yellow stripe on top of the head. The male also has a red crest within this golden crown, visible only when the crest is raised in excitement, such as when trying to attract a mate or defending territory. The bill is short and thin. The other kinglet found in North America, the ruby-crowned, is much plainer and generally seen here only in spring and fall migration.

Kinglets are very active birds, flitting around branches, flicking their wings, sometimes hovering off the end of a branch. It seems as though they never sit still. Their call is very high-pitched, slightly buzzy, generally three similar notes – szee-szee-szee – and can be hard to hear, especially for those who have attended too many rock concerts. The high pitch makes the source difficult to locate, and despite their almost constant movement, they can be infuriatingly hard to locate high in conifers.

Where and when?

I have seen and heard golden-crowned kinglets in several places around Carlisle since the beginning of October. One of the best places to find them is on the Woodchuck Trail in Great Brook State Park near the canoe launch. On the Carlisle section of the Christmas Bird Count (south of Route 225), going back to 1973, they have been recorded every year except for 1991 and 2007, with a high count of 37 in 1986.

Their breeding range stretches all across southern Canada and down into the Rockies and northern New England. A pair found nesting in Weston just last year was the first confirmed breeding record for Middlesex County. They are most common here in April and especially October as migrating birds pass through. Most of them move to the southern half of the country for the winter, but varying numbers remain here (and indeed farther north) through the winter. They generally nest in spruce forests, but in winter and during migration they are often found in white pine or mixed woods, of which Carlisle has plenty.

How?

So how does such a small bird, one that does not eat seeds but insects, survive the northern winter? How does it find food? How does it stay warm? The answers, or at least some fascinating discussion about those questions, can be found in Winter World, Bernd Heinrich’s wonderfully eccentric account of “the ingenuity of animal survival,” with the Golden-crowned Kinglet playing a starring role.

It is much more difficult for smaller animals to conserve body heat, because of the larger ratio of surface area to mass, which is why northern birds and animals are generally larger than their southern counterparts. This is known as Bergmann’s Rule and our kinglet is an extreme exception. How they survive long, cold winter nights seems to defy science and is not fully understood, but it seems to be a combination of several factors in perfect balance, with virtually no margin for error. The kinglet’s down is about an inch thick (the body underneath is not much larger than a cherry) and fluffing out those feathers helps with insulation. The head and feet are where most heat is lost, so it sleeps with them tucked under its feathers. Compared to other birds, a larger proportion of its feathers (about 80%) are devoted to insulation rather than flight. That tends to make them fairly weak fliers, so surviving migration can be as difficult as surviving the winter.

Golden-crowned Kinglets usually forage in small groups of two to six birds and probably huddle together as a group in a sheltered place at night to keep warm, but apparently lower their body temperature (becoming hypothermic), and perhaps even enter a state of torpor or “microhibernation” to conserve energy. Staying together as a group is important, so they stay in contact with frequent calls.

During the day, they need to add sufficient energy in the form of body fat to carry them through the night. Their constant activity from sunrise to sunset helps to keep them warm, but they need to eat almost continuously, consuming two to three times their body weight each day, to provide the energy to keep moving. Insects are not the easiest food to find in winter in New England. The thin bill allows them to pick out hibernating insects in twigs and bark, but the main part of their diet is tiny, inchworm caterpillars that they often find near the ends of twigs. How those caterpillars survive the winter is a whole other story, one involving natural anti-freeze, but you’ll have to read Winter World for that.

Kinglets are often found in mixed winter flocks with other birds, such as chickadees, titmice and nuthatches. The mixed group provides safety in numbers with more eyes to detect predators and perhaps more sophisticated teamwork taking advantage of different abilities.

The extent to which the Golden-crowned Kinglet is “living on the edge” is perhaps best illustrated by their survival rates. Although the longest-lived individual found in the wild was almost five years old, the mortality rate each year is higher than 85%, making it almost the avian equivalent of an annual in the plant world. To compensate for this it produces lots of young, hatching ten or more eggs and, in many cases, building a second nest with another ten. The nestling success rate of 80% is extremely high.

Field trip

If you would like to see a Golden-crowned Kinglet, meet at 8:30 on Sunday morning, December 6, at the main parking lot at Great Brook Farm State Park. From there, we will carpool to the small parking area at the canoe launch and walk the Woodchuck Trail in search of these tiny birds. Bring binoculars if you have them.

References

Massachusetts Breeding Bird Atlas, edited by Wayne R. Peterson and W. Roger Meservey; The Sibley Guide to Birds, David Allen Sibley; The Birders’ Handbook, Paul R. Ehrlich, David S. Dobkin and Darryl Wheye; Winter World, by Bernd Heinrich; ∆


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