Ruby-crowned kinglets and golden-crowned kinglets are two very similar North American bird species in the genus Regulus. They are among the smallest passerines in North America and can be challenging for birders to distinguish in the field due to their tiny size and active foraging behavior. However, they can be told apart by several key physical differences as well as some subtle variations in habitat preference and behavior.
Physical Appearance
In terms of physical appearance, ruby-crowned kinglets and golden-crowned kinglets differ most noticeably in the coloration of the crown feathers on the top of their heads. As their names suggest, ruby-crowned kinglets have a distinctive ruby-red crown patch, while golden-crowned kinglets have an orangey-yellow crown patch. The crown feathers are normally flattened, but can be raised briefly to reveal the colorful patches.
Some other differences in plumage:
- Ruby-crowned kinglets have olive-green upperparts and white underparts with buffy flanks. They have two narrow white wing bars.
- Golden-crowned kinglets have olive-green upperparts and buffy underparts with whitish belly. They have one broader white wing bar.
- Ruby-crowned kinglets have thin, sharply pointed bills. Golden-crowned kinglets have shorter, more conical bills.
- Male ruby-crowned kinglets have a black stripe through the eye. Golden-crowned kinglets lack this stripe.
In general, ruby-crowned kinglets have more contrast between the green upperparts and white underparts compared to golden-crowned kinglets which have more buffy olive coloration throughout. But in the field, the crown color is the most obvious difference.
Size and Weight
Both ruby and golden-crowned kinglets are tiny birds, though on average, golden-crowned kinglets are ever-so-slightly larger:
Species | Length (cm) | Wingspan (cm) | Weight (g) |
---|---|---|---|
Ruby-crowned kinglet | 10-12 | 16-18 | 5-7 |
Golden-crowned kinglet | 11-13 | 17-20 | 6-10 |
So while there is some overlap, golden-crowned kinglets are generally slightly stockier with a quarter-inch longer body and broader wingspan. But the differences are subtle and variable enough that size alone is not a reliable identification marker.
Song and Call
Ruby and golden-crowned kinglets can also be distinguished by differences in their vocalizations:
- Ruby-crowned kinglets have a quick, high-pitched call described as “tse-tse-tse-tse” or “zwee-zwee-zwee.”
- Golden-crowned kinglets have a call more like “tsee-tsee” or “zee-zee.” Slower and not as hurried sounding as the ruby-crowned kinglet.
- The song of ruby-crowned kinglets is a series of high-pitched notes and trills ending in a rapid warble. Often transliterated as “si ti ti ti ti tu tu.”
- Golden-crowned kinglets have a song that is a rapid jumble of twitters, chips, and trills. Less musical and more variable than the ruby-crowned kinglet’s song.
So while their calls are quite similar, attentive listening can pick up on the faster, higher frequency of the ruby-crowned kinglet vocalizations compared to the golden-crowned kinglet.
Range and Habitat
Ruby and golden-crowned kinglets occupy broadly overlapping ranges across Canada, the western and northeastern United States, and down into Central America. However, there are some habitat preferences that differ between the species:
- Ruby-crowned kinglets are more associated with coniferous forests, especially young stands of spruce and fir. They prefer the lower and middle levels of open forests.
- Golden-crowned kinglets make greater use of mixed and deciduous forests. They frequent the upper canopies of mature, dense hardwood stands.
- During migration and winter, ruby-crowned kinglets use a wider variety of wooded habitats including parks and suburban areas with tall trees. Golden-crowned kinglets tend to stick closer to deep forest interiors.
So while their breeding ranges overlap extensively, ruby-crowned kinglets are more of a coniferous forest specialist, while golden-crowned kinglets are more closely tied to dense deciduous stands. Hybridization between the species can occasionally occur where their habitats merge.
Behavior and Feeding
Ruby and golden-crowned kinglets forage actively in the trees for small insects and spiders, often joining mixed-species foraging flocks in the nonbreeding season. Some behavioral differences:
- Ruby-crowned kinglets feed by gleaning insects from the outer foliage and making short sallies and hover-gleans going after insects. They start from the lower canopy and work their way up.
- Golden-crowned kinglets tend to forage higher in the trees, feeding primarily on small insects like aphids, psyllids, and bark lice gleaned from the inner foliage.
- Ruby-crowned kinglets are more adaptable to a variety of foraging techniques and will readily come to feeders. Golden-crowned kinglets strongly prefer to forage in the leafy canopy.
- Ruby-crowned kinglets are more solitary in the winter, while golden-crowned kinglets remain social and continue to travel in flocks outside the breeding season.
So while both species are active foragers, ruby-crowned kinglets cover more territory and will make use of a wider range of food sources. Golden-crowned kinglets tend to be more specialized canopy-foragers.
Breeding
The breeding ecology of these two kinglet species also shows some slight differences:
- Ruby-crowned kinglets often nest in conifers like spruce and fir, especially young trees around forest edges and openings. The nest is well-concealed in a natural tree cranny or old woodpecker cavity.
- Golden-crowned kinglets nest primarily in mature deciduous trees, tucked into crevices of the bark or clumps of lichens and moss. Favorite nest sites include oak, hickory, birch, and beech.
- Ruby-crowned kinglets have higher nesting success rates compared to golden-crowned kinglets.
- Clutch sizes are similar with 6-9 creamy white eggs laid in a cup nest built from mosses, lichens, feathers, and spider webs.
- Ruby-crowned kinglets are frequent hosts of brown-headed cowbird nest parasitism. Golden-crowned kinglets are less prone to brood parasitism.
So ruby-crowned kinglets are more flexible in their nest-site selection while golden-crowned kinglets have very specific requirements. Both invest heavily in well-hidden nests to avoid predation.
Migration
As North American breeders, ruby and golden-crowned kinglets are both strongly migratory:
- Ruby-crowned kinglets winter primarily in the southern U.S. and Mexico. They migrate relatively early in fall and show up late in spring.
- Golden-crowned kinglets winter farther south, down to Guatemala and the West Indies. They migrate later in fall and arrive earlier in spring on the breeding grounds.
- Ruby-crowned kinglets make extensive overwater crossings of the Gulf of Mexico and Caribbean. Golden-crowned kinglets tend to “island hop” and follow more coastal routes.
- Ruby-crowned kinglets often linger and make return migrations in the southern part of their range. Golden-crowned kinglets carry out more distinct and direct migrations between breeding and wintering areas.
So ruby-crowned kinglets follow a “leapfrog” migration pattern while golden-crowned kinglets are more strictly “latitudes migrants.” Both species form large mixed-species flocks during migration.
Taxonomy
Ruby and golden-crowned kinglets were formerly considered to be one species – the “ruby-crowned kinglet.” They were split into separate species based on morphological, vocal, and genetic differences. Here is how they are classified:
- Ruby-crowned kinglet – Regulus calendula
- Golden-crowned kinglet – Regulus satrapa
- Both are in the kinglet family Regulidae. This is in the larger parvorder Passerida of the order Passeriformes (perching birds).
- DNA analysis suggests ruby and golden-crowned kinglets diverged around 2.2 million years ago, likely driven by habitat specialization.
- There are 6 other Regulus kinglet species worldwide, but the ruby and golden-crowned are the only members of the genus found in the Americas.
Conservation Status
Despite some population declines linked to deforestation and loss of wintering habitats, neither ruby nor golden crowned kinglets are considered threatened species currently:
- Ruby-crowned kinglet:
- IUCN Red List: Least Concern
- Population: Estimated global breeding population of 19 million
- Golden-crowned kinglet:
- IUCN Red List: Least Concern
- Population: Estimated global breeding population of 10 million
Their tiny sizes and high metabolisms require abundant food sources and make them vulnerable in degraded habitats. But maintaining connected forest landscapes through responsible logging and development practices can ensure the long-term survival of both species.
Conclusion
In summary, ruby and golden-crowned kinglets can be very challenging to distinguish in the field due to their diminutive size, active movements, and similar olive-green plumage. Focusing on the crown color, subtle plumage variations, vocalizations, foraging behavior, and habitat preferences are the best ways to positively identify these species. While requiring specialized techniques to separate, being able to differentiate these two tiny, gem-crowned sprites provides an accomplishment and skill-builder for birders of any experience level.