Ruby-crowned kinglets are small birds with an olive-green coloration. Males and females are about the same size and shape, although males have a small patch of red feathers on the top of their head, a feature not seen in females and young birds. Ruby-crowned kinglets have two white wing bars and a broken, white eye-ring. Their under parts are off-white, their lower back feathers are olive-green with white bars on the middle of each feather, and their wing feathers are grayish with green edges and white tips. Their legs and feet are brown, to yellowish-brown near their toes. Their bill is blackish brown, thin, and pointed. Their mouth lining is orange in adults and bright red in hatchlings. Juveniles have brownish upper parts and off-white wing bars. Ruby-crowned kinglets are most often confused with Hutton's vireos due to their color and the way they flick their wings, in comparison however, ruby-crowned kinglets are much more active. (Alderfer, 2006; Ingold and Wallace, 2008; Pettingill, 1985; Sterry and Small, 2009; Terres, 1980)
Ruby-crowned kinglets (Regulus calendula) are found in northern, western, and some eastern parts of North America. They breed in Alaska, Canada, parts of the Rocky Mountains, and the northern parts of the Great Lakes. Ruby-crowned kinglets can be found in parts of the western United States and southwestern Canada year-round. Their winter range includes the southeastern to western United States and dips south into Mexico and Central America. ("California Wildlife Habitat Relationships System", 1988; Ingold and Wallace, 2008; Lepthien and Bock, 1976; Swanson, et al., 1999)
Ruby-crowned kinglets can live in woodlands, thickets, and open or edge habitats. During their spring and fall migration, they are found in coniferous, deciduous, and floodplain forests, as well as suburban yards. In their winter range, they prefer forests in low-laying lands. During winter migration, they are found in tropical riverside forests, semi-humid forests and woodlands, tropical semi-deciduous forests, and dry pine-oak forests in Central America and Mexico. They can be found from 450 to 3,000 m in elevation. ("California Wildlife Habitat Relationships System", 1988; Alderfer, 2006; Arlott, 2011; Ingold and Wallace, 2008; Laurenzi, et al., 1982; Lepthien and Bock, 1976; Rappole, 2006; Sterry and Small, 2009)
Ruby-crowned kinglets are monogamous, meaning that males and females only mate with one bird during the breeding season. Each new breeding season, ruby-crowned kinglets find a new mate. A male begin courtship by approaching a female and hopping from branch to branch with his tail raised and his red crown visible. The male sings and in response, the female flutters her wings, the male moves closer to the female and they disappear behind shrubbery to mate. (Ingold and Wallace, 2008)
Ruby-crowned kinglets usually have one brood each year. During the first week of May, females choose a nesting site, carry nest materials, and build nests in about five days. Nesting trees are usually about 16 m tall and nests are generally found at 12 m. Their nests are protected by canopies and may blend in with tree trunks. The outside of their nests are made of mosses, lichens, feathers, cocoon silk, spider webs, pieces of bark, twigs, roots, grasses, and conifer needles, while the lining is made of feathers, fine grasses, plants, lichens, and animal fur. Their nests expand as their brood gets larger and are usually 10 cm across and 12 to 15 cm deep. Female ruby-crowned kinglets lay 5 to 11 eggs per brood. Their eggs appear nearly identical to those of golden-crowned kinglets, they are smooth, with a rounded oval shape and can be pure white or off white, they are also spotted with a brownish color and occasionally have a circle around the large end. Females lay eggs in about 8 to 12 days. They begin incubating shortly after they build their nest in late May to early June and continue for about 12 to 14 days. When incubating, the female buries herself in the nest and sits on top of her eggs; they also groom themselves often and take breaks by standing on a branch next to the nest. When ruby-crowned kinglets hatch in mid-June, they are altricial, meaning they are mostly naked and helpless, and parents begin feeding them immediately. They fledge about 12 to 19 days after hatching (typically early July), and become restless and energetic about a week beforehand. Young kinglets start vocalizing when they leave their nest. They become sexually mature in about 1 year. (Farley, 1993; Ingold and Wallace, 2008; Terres, 1980)
Male ruby-crowned kinglets feed the females while they incubate the eggs, especially during cold weather. In warmer weather, females leave the nest for about five minutes at a time to find food. Females do all of the brooding of the eggs and nestlings. Males usually feed the newly hatched chicks by regurgitation while the female broods. Both parents feed the young and keep the nest clean by removing fecal matter. In one study, a chick attempted to jump from the nest early, but the male pushed the chick back into the nest for safety. (Ingold and Wallace, 2008)
The longest recorded lifespan for ruby-crowned kinglets is 5 years and 7 months in the wild. They are not usually kept in captivity. (De Magalhaes and Costa, 2009; Ingold and Wallace, 2008; Klimkiewicz, et al., 1983)
Ruby-crowned kinglets spend their time flying, foraging, nesting, hopping, sleeping, and roosting, although most of their time is spent foraging for food. They hover to search for insects in trees and under leaves, similar to golden-crowned kinglets. They also fly to search for insects. They forage mostly on twigs and branches in taller trees. While they are foraging, they flick their wings continuously. Kinglets usually roost alone on tree branches close to the trunk. Male kinglets may become aggressive when they face a rival. During aggressive displays, males lean forward, with their red crown up and their rump in the air, showing off the white bars on their tail. They flash their wings and turn from side to side while singing and moving their head from side to side slowly. In the winter, they are aggressive to Carolina chickadees, yellow-rumped warblers and orange-crowned warblers by chasing and sometimes attacking them. They are more aggressive toward golden-crowned kinglets than other ruby-crowned kinglets. Males migrate earlier in the spring than females, and in the fall, females migrate earlier than males. (Franzreb, 1984; Ingold and Wallace, 2008; Keast and Saunders, 1991; Laurenzi, et al., 1982; Rappole, 2006; Sterry and Small, 2009; Swanson, et al., 1999; Terres, 1980)
Ruby-crowned kinglets live in large territories of 1.1 to 6.0 hectares, which include their nests and their needed resources. ("California Wildlife Habitat Relationships System", 1988; Ingold and Wallace, 2008)
Ruby-crowned kinglets mostly communicate with vocalizations, such as songs and calls. There are four kinds of vocalizations. The first type is a song, which is mostly produced by males and includes a complex series of loud chattering and warbling notes. They mostly sing on their breeding grounds, but they may also be heard on their wintering grounds and during spring migration. The second type is an alarm call, which includes two variations. The third vocalization is a simple contact call, which is used to communicate with other ruby-crowned kinglets. The final vocalization is the begging call, produced by chicks when they leave the nests; this is usually the first type of vocalization produced by the birds. When male kinglets communicate by displaying, they typically sing, whether they have a male audience or not. Males stand up straight and puff the feathers on their rump and crown. When other males are present, they move as though they are performing a dance, moving side to side, with their rump and red crown puffed out. When they face a rival, they add to their display by flapping their wings and turning from side to side. (Ingold and Wallace, 2008; Päckert, et al., 2003; Rappole, 2006; Sterry and Small, 2009)
Ruby-crowned kinglets mostly eat insects and spiders, but prefer flying insects. They mostly eat scale insects, mealy bugs, beetles, flies, wasps, ants, and moths. They also eat pseudoscorpions, some fruit, hardened seeds, and other vegetable matter, as well as various kinds of berries, such as elderberries and wax myrtle berries and they occasionally drink tree sap. Their diet does not change very much during different seasons. During the winter and migration, they eat insects and their eggs, spiders and their eggs, hardened seeds, various fruit, and vegetable matter, although they do not eat vegetable matter during their breeding season. (Franzreb, 1984; Ingold and Wallace, 2008; Keast and Saunders, 1991; Laurenzi, et al., 1982; Terres, 1980)
Ruby-crowned kinglets may be preyed on by large birds and small mammals, including eastern-screech owls, sharp-shinned hawks, merlins, common grackles, gray jays, and red squirrels. In addition, gray jays are known to eat their eggs and red squirrels may destroy their nests. Ruby-crowned kinglets may also be harmed by the thorns of certain plants, such as greenbrier. Likewise, the sticky seeds of beggar's lice may attach to their feathers. (Forsman and Martin, 2009; Ingold and Wallace, 2008; Shackelford and Shackelford, 2001)
Ruby-crowned kinglets are known to carry ticks (Ixodes dentatus and Haemaphysalis leporispalustris), mites (Proctophyllodes longiquadratus and Ptilonyssus acrocephali), and hippoboscid flies (Ornithomyia confluent). They may also carry avian malaria (Leucocytozoon) and encephalitis. Brown-headed cowbirds occasionally lay their eggs in ruby-crowned kinglets' nests, but they usually choose to lay their eggs in the nests of larger birds. (Forsman and Martin, 2009; Holt, 1942; Ingold and Wallace, 2008; McCurdy, et al., 1998; Spicer, 1987)
There are no known negative effects of ruby-crowned kinglets on humans. (Ingold and Wallace, 2008)
By eating insects, ruby-crowned kinglets help control pest populations. Many of the insects they eat are considered pests to humans. They also eat invasive insect species, such as larch casebearers, which may be harmful to certain plants. (Ingold and Wallace, 2008; Sloan and Coppel, 1968)
Ruby-crowned kinglets are a species of least concern according to the IUCN Red List of Threatened Species, and may actually have a growing population, although populations in eastern North America may be slightly decreasing. Ruby-crowned kinglets are negatively affected by the wildfires and logging that occurs in their habitats. One subspecies, Regulus calendula obscurus is likely extinct. This subspecies was known from a single island (Guadalupe Island in Mexico) and has not been seen in over 60 years. (BirdLife International, 2012; Ingold and Wallace, 2008; Sauer, et al., 2013)
Amanda Pendergrass (author), Radford University, Karen Powers (editor), Radford University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
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