Olive-gray above; dusky colored under parts; wings black with two white wing bars; ruby-colored crown patch on the males (not always visible). 11 cm (4.25 in) in length.
This species does not breed in the Southeast, but the breeding season begins in late May and extends to mid-July. Nesting usually occurs in conifer or mixed-conifer forest. The nest is usually 4.5-9 m (15-30 feet) high in a conifer. The female builds the nest out of moss, lichen, leaves, and spider webs. The nest is suspended under a branch, usually near the branch's outer edge. The female lays 5-11 (usually 7-9) eggs that she incubates for approximately 12 days. The young are altricial and fledge about 12 days after hatching. Both the male and female tend to the young while they are in the nest and for a period after fledging.
The primary habitat of the Ruby-crowned Kinglet is coniferous forests, but also includes mixed forests. The diet consists mostly of insects and spiders and occasionally seeds, fruits, and tree sap. This kinglet forages by moving among the tree branches and leaves, moving its wings to flush prey. It also picks insects off of branches, leaves, and needles of the trees. This species is migratory.
The Ruby-crowned Kinglet breeds in the western United States and Canada. Wintering birds occur throughout the southern United States, with some birds wintering as far south as Guatemala. In the Southeast they are common during the winter except in the mountain regions and in extreme southern Florida.
This species is common in appropriate habitat and season, and is not listed as Threatened or Endangered in any part of its southeastern range.
The species most similar to the Ruby-crowned Kinglet is the Golden-crowned Kinglet. The Golden-crowned Kinglet has a white eye brow, dark eye stripe, and a yellow and black border around its orange (male) or yellow (female) crown patch. Those characteristics plus the whiter underparts distinguish the Golden-crowned Kinglet from the Ruby-crowned Kinglet.