One of my favorite spring migrants is a delightful sprite, the ruby-crowned kinglet. The average arrival date in Maine is around Tax Day and a few will arrive by the first of April.

Ruby-crowned kinglets spend their winter in the southern parts of the United States into Mexico. We think of them as short-distance migrants because they do not leave our continent, flying over open ocean to get to South America as bobolinks or Blackburnian warblers do.

We have a second kinglet in the state, the golden-crowned kinglet, that is a year-round resident. These two closely related species show some rather striking differences. But first, let’s look at the similarities.

These two species are the smallest songbirds we have in the state, each at about seven grams or less than the weight of three pennies. The black-capped chickadee has twice the mass of a kinglet. The only smaller bird in the state is the ruby-throated hummingbird.

The kinglets belong to the genus Regulus. Translated from the Latin, Regulus means small king. I think you will agree that kinglet is a cooler translation.

Kings wear crowns and that is the case for both kinglets. The ruby-crowned kinglet males have a crown of red feathers that are usually obscured by gray feathers. The crown of both male and female golden-crowned kinglets has a couple of black stripes separating a central lemon-yellow patch. Those yellow feathers hide metallic orange feathers.

These crowns are very important in social signaling. When a kinglet becomes aggressive toward another kinglet, it will expose its red or orange feathers, signaling its willingness to fight.

In the summer, both kinglets are primarily insect-eaters. Like most of our other leaf-gleaning insectivores like warblers, vireos and tanagers, ruby-crowns migrate in the fall.

We do have some year-round species like chickadees, nuthatches and titmice that primarily eat insects in the summer but switch their diet to seeds to get through the winter.

The golden-crowned kinglet has a different strategy. It is a resident species but does not give up its meat-eating ways in the winter. Instead, it forages for insects and spiders that have allowed their bodies to freeze in a controlled way to survive the winter. The kinglets forage at the tips of conifer branches and underneath bark scales on those conifers where the invertebrates are overwintering.

The ability of golden-crowned kinglets to survive the winter astounds me. Small warm-blooded animals are greatly disadvantaged by geometry. The laws of geometry result in small objects having a high surface-to-volume ratio. Heat is lost across the surface and must be replaced by the cells in the volume of the body. The modest number of cells in the body of a kinglet must work hard to replace the heat lost across the relatively large surface. Small birds and mammals are really living on the edge during the winter.

To reduce the rate of heat loss, golden-crowned kinglets will huddle together at night on the tips of exposed conifer branches. Some of the heat lost by each bird is absorbed by a neighbor.

The two species of kinglets differ in their vocalizations. Golden-crowned kinglets have a very high-pitched “tsee” contact call throughout the year. This note is one of the first to go for birders experiencing some hearing loss as they age. The song is a series of thin, high-pitched ascending notes.

Ruby-crowned kinglets are much easier to detect by ear. Their contact call can be described as “che-dit” and is often given in a series. It’s easy to pick up and highly distinctive.

The song is a complex series of galloping notes and trills that are surprisingly loud for such a small bird. The song is audible for over half a mile in open habitat.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu

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