Goldcrests, Kinglets

Kinglets, small members of the Regulidae family, are tiny birds earlier grouped with Old World warblers. Known for their brightly colored crowns in males, which gave them their regal name, they inhabit North America and Eurasia, comprising six species including the recently recognized Madeira firecrest. These birds are among the smallest passerines, measuring 8 to 11 cm in length and weighing just 6–8 grams, with similar size dimorphism between sexes. Characterized by grey-green plumage, pale wingbars, and a distinctive head marking, they also differ in some adaptations; for instance, conifer specialists have modifications allowing them to perch on twigs and cling on vertically, whereas the generalists, who tend to hunt more in flight, have smoother soles, shorter hind claws, and longer tails. Their taxonomy has evolved, with most kinglets sharing the genus Regulus, except for the ruby-crowned kinglet given its unique vocal patterns and plumage, placed in its own genus Corthylio. Kinglets can be found across temperate zones of the Nearctic and Palearctic realms, adept at living in conifer forests, though they show habitat adaptability, especially during migration. Kinglets have a high metabolism, necessitating continuous foraging, primarily on insects with soft cuticles. Their nests, small and insulated with moss, lichen, and spiderwebs, are placed on conifer branches. Females lay 7 to 12 eggs in layers due to space constraints, with a unique egg "size hierarchy." Kinglet eggs hatch asynchronously after 15 to 17 days, and the young, which leave the nest after 19 to 24 days, demonstrate a survival challenge within the nest hierarchy. Despite their high reproduction rate, kinglets have short lifespans. Adult mortality is steep, particularly for the goldcrest, with an estimated 80 percent yearly mortality rate and a maximum lifespan of only six years, making them some of the most ephemeral of all altricial birds.