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a family of birds of the order Passeriformes. Related to the Sylviidae, the Regulidae are small birds with soft, downy plumage. The family comprises seven species, which are distributed in the forests of the northern hemisphere. There are three species in the USSR. The most common is the goldcrest (Regulus regulus), the smallest bird in the USSR. Its body measures up to 10 cm long and it weighs 5–6 g. The plumage is gray-green. The males have an orange crown, and the females have a black-bordered yellow crown. The goldcrest lives in fir or spruce forests from the western borders of the USSR to the Kuril Islands. The Regulidae suspend their almost spherical nests from the branches of trees. The clutch contains five to ten eggs. In the winter the birds migrate in flocks, often together with the Pari-dae. The Regulidae feed on insects. The firecrest (R. igni-capillus) is found in the forests of the western Ukraine, the Crimea, and Transcaucasia. The lilac-colored crested tit-warbler (Leptopoecile sophiae) inhabits thickets of savin in the Tien-Shan.