Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [121]
Taxonomically, kinglets have long been a puzzle. Bent placed them among the thrushes and their allies. They have also been assigned to the titmice family, Paridae. They were thought closely related to the Old World warblers, subfamily Sylviinae (as opposed to the New World warblers, Parulidae). However, DNA studies (Sibley and Ahlquist 1985) suggest that they are of another descent (Ingold and Galati 1997); they are now known to be unrelated to either thrushes, tits, or warblers (Sheldon and Gill 1996). They are different, and unique.
In Europe there are two species of kinglets, the goldcrest Regulus regulus and the firecrest Regulus ignicapillus. Both species are relatively sedentary, but not entirely so as they have a tendency to migrate north and south within Europe. In North America there are also two species of kinglets. The ruby-crowned kinglet (Regulus calendula) breeds in Alaska and throughout Canada and migrates in the winter to Mexico and the southern United States. In contrast, the golden-crowned Regulus satrapa occurs throughout the United States and southern Canada in winter and summer, although part of the population also migrates into northern Canada to breed there.
Despite the depictions in most bird books, recent studies of the kinglet’s proteins (Ingold, Weight, and Guttman 1988) indicate that there are substantial genetic differences between the two American species. These differences are large enough to warrant putting them into different genera. On the other hand, our North American golden-crowned kinglets are nearly indistinguishable from the European and Asiatic goldcrest. Even their songs are nearly identical (Desfayes 1965). They could easily be lumped into the same species, although for perhaps no other than practical purposes they currently aren’t. For practical purposes I also restrict my discussion to the North American golden-crowned kinglet.
The golden-crowned kinglet’s ability to hold on in the north, where insect food is plentiful in summer and scarce in winter, is in no small measure dependent on its nesting behavior. Kinglets produce many young that compensate not so much for a high nestling mortality as in most other northern songbirds, but for a high winter mortality. Their nesting behavior is noteworthy in several ways. First, even in Maine and in Nova Scotia, where the deciduous trees don’t leaf out until mid-May, the kinglets already start nest-building in mid-April. Snowstorms are still common at that time and if kinglets built their nests like many other birds, then these nests would often be buried under snow. However, unlike crossbills, kinglets build their nests suspended under spruce branches where they are covered from above by a thick latticework of twigs and needles. Here the nest is virtually invisible from above and therefore well protected from most predators, and if the branches over a nest get covered with a thick layer of snow then all the better, because the nest is then inside a snug insulating snow cave.
Cold is still a potential problem early in the year, but a kinglet’s nest is built for warmth. Few people have observed the nest-building process, and even fewer have described it. I quote here a detailed set of observations of Miss Cordelia J. Stanwood, of Ellsworth, Maine, whose notes were published by Bent (1964, p. 386):
Golden-crowned kinglet beginning to build a nest.
The kinglets selected for the roof of their cradle a heavy spruce limb with a dense tip; and the female, hopping down through the branch from twig to twig, attached her pensile nest to the sprays.
The bird wove her spherical structure about herself much as the caterpillar of the luna or cecropia moth weaves its cocoon about itself, except that the kinglet had to gather her materials. The bird stood on a twig on one side of the space she had chosen for her nest and measured off her length, as far as the situation of the twigs would permit, by attaching bits of spider’s silk and moss to the twigs. Thus