Blue-Throated Mountain-Gem: King of the US Hummingbirds

Male Appearance

The male Blue-throated Mountain-Gem is distinguished by a combination of features impossible to confuse with any other North American hummingbird. The throat is a true, matte blue --- not iridescent, not changeable, simply blue --- a subtle gorget compared to the more flashy gorgets of smaller species but all the more striking for its permanence. The rest of the plumage is deep metallic green above and grayish-green below. The tail is long, broad, and dark, with very conspicuous white corners on the outer tail feathers --- these white outer-tail flashes are visible from twenty meters or more and are the most reliable long-distance field mark. Two white facial stripes --- above and below the eye --- bracket a dark face. The bill is long, straight, and black. In flight the large body size and slower wingbeat create an impression quite different from smaller canyon hummingbirds.

Female Appearance

The female Blue-throated Mountain-Gem is recognizable even among large female hummingbirds. She is plain gray-green above and medium gray below, lacking any spotting or streaking on the throat --- this clean, plain underpart distinguishes her from the spotted female Rivoli's. The same bold white facial stripes (supercilium and malar stripe) present in the male are equally visible on the female --- two clear white lines on either side of a darkish face --- making this a highly distinctive and useful mark. The tail shows the same large white outer corners as the male, equally conspicuous in flight. She is, simply, a large, gray-green hummingbird with white face stripes and white tail corners --- a combination that identifies her unambiguously in Arizona or Texas.

Similar Species & How to Tell Them Apart

• Rivoli's Hummingbird --- The only species approaching Blue-throated in size. Male Rivoli's has purple crown and green gorget, no blue throat, no white tail corners. Female Rivoli's is heavily spotted/streaked below, not plain gray like female Blue-throated.

• Broad-billed Hummingbird --- Much smaller; male is all blue-green with a red bill, no white tail corners.

• All other Arizona hummingbirds --- Substantially smaller; none combine the white tail corners with the plain gray underside and bold white facial stripes of the Blue-throated female.

The white tail corners are diagnostic at any distance. Once this mark is learned, Blue-throated Mountain-Gem ID is immediate.

• April--May: First Blue-throated Mountain-Gems arrive at Arizona canyon sites; birds at Chisos Basin (TX) generally arrive in April.

• May--July: Peak breeding season; males sing persistently, females incubate.

• July--August: Monsoon season; still active at feeders and natural flowers; young of year begin appearing.

• September--October: Most birds depart; some individuals --- particularly at lower-elevation Arizona sites --- have been documented overwintering.

• November--March: Rare winter records at SE Arizona feeder stations; a small number of individuals apparently winter annually.

Best timing: May through August for the full breeding experience. Cave Creek Canyon and Miller Canyon in June--July offer the best combination of Blue-throated activity and overall hummingbird diversity.

• Large-capacity feeders: Given the Blue-throated's body size and dominant feeder position, larger feeders with wide ports and sturdy perches are appropriate. The bird's bill fits standard ports comfortably.

• Multiple feeders: Because Blue-throateds will monopolize a single feeder and exclude all others, running six or more feeders at a property distributes dominant individuals and allows the full diversity of canyon species to feed. This is standard practice at productive Arizona canyon feeding stations.

• High placement: Blue-throateds are comfortable at height; feeders at 6--10 feet or suspended from canyon-edge trees are appropriate.

• Ant moats and regular cleaning: In summer canyon heat, change nectar every 2--3 days. Blue-throated Mountain-Gems are less tolerant of fermented nectar than the caloric desperation of migration sometimes forces smaller birds to accept.

• Observation setups: These are large birds that tolerate patient observers. Position a chair within 10--15 feet of a feeder at an established canyon station and Blue-throateds will feed comfortably while being observed and photographed at close range.

The Blue-throated Mountain-Gem breeds in the United States --- one of only a few Mexican hummingbird species to do so regularly. The nest is a remarkably large cup structure relative to other US hummingbirds, reflecting the bird's size; it is made of plant fibers, moss, and spider silk and is frequently built on or over water --- on a ledge behind a small waterfall, on a root mass overhanging a stream, or on a rocky overhang in a canyon wet zone. This preference for wet microsites is unusual among hummingbirds and has been noted by multiple researchers.

The female incubates two white eggs for approximately 17--19 days. Young fledge at roughly 24--29 days. The species is highly site-faithful and will reuse or rebuild nests at the same location in successive years.

Most remarkable reproductive behavior: Unlike every other hummingbird species in the United States --- in which the male sings only as part of territorial advertisement or courtship display --- the Blue-throated Mountain-Gem female sings back during courtship, creating a true duet between paired birds. This behavior is unique among US hummingbirds and has drawn attention from researchers studying the evolution of hummingbird vocal complexity.

The Blue-throated Mountain-Gem is classified as Least Concern (IUCN). It is fairly common throughout appropriate high-elevation habitat in the Sierra Madre Occidental and Sierra Madre Oriental of Mexico. The US breeding population --- concentrated in a few dozen canyon sites in AZ, NM, and TX --- is small in absolute numbers but appears stable.

Conservation concern for this species in the US context mirrors that for other sky-island specialists: long-term water availability in canyon systems, drought impacts on riparian vegetation, and climate-driven upward shifts in vegetation zones (which could compress or eliminate habitat at lower-elevation canyon sites). The US Forest Service's management of the Coronado National Forest (which encompasses much of the Huachuca, Chiricahua, Santa Rita, and Pinaleno mountains) and the National Park Service's management of Big Bend directly influence the long-term viability of Blue-throated Mountain-Gem habitat in the United States.