Introduction

The Ruby-crowned Kinglet, one of North America’s smallest songbirds, has a loud, complex song and, with up to 12 eggs, lays the largest clutch of any North American passerine for its size. Males and females are nearly identical in plumage, being olive green-gray on the upperparts with two strong white wing-bars and a broken, white eye-ring. The male has a crown patch, usually concealed, which may be either scarlet to yellow, or absent.

During migration and winter, the Ruby-crowned Kinglet occupies a variety of habitats and is often recognized by its constant wing-flicking. As a breeder, it inhabits spruce-fir forests of the northern and mountainous western United States and Canada. Its nest is hidden, often near the trunk and up to 30 meters above the ground, making reproductive data difficult to gather. Much remains to be learned about the breeding biology and behavior of this species.

The Ruby-crowned Kinglet winters farther south than the hardier Golden-crowned Kinglet (Regulus satrapa), and its winter range appears to be determined primarily by temperature. Its breadth of habitat choices during migration and the nonbreeding season has allowed the species to escape the influences of most human disturbances, although a resident population on Gaudalupe Island off Baja California may have been extirpated, and western populations may be affected by logging activities.