Blue-throated Mountain-gem Life History

Habitat

In Arizona, New Mexico, and Texas Blue-throated Mountain-gems inhabit cool coniferous and mixed woodlands in the mountains. They forage mostly in the understory, in flower-rich areas along flowing streams, usually between 4,500 and 11,500 feet elevation but sometimes as low as 3,200 feet. In Mexico, the species may live even higher, to 12,800 feet. Blue-throated Mountain-gems mainly use pine-fir and pine-oak forests, where they forage mostly in gaps and along streams that flow through canyons, areas that are usually filled with flowers during the rainy season. Common tree species include Arizona sycamore, bigtooth maple, Chihuahua pine, Apache pine, ponderosa pine, silverleaf oak, Arizona white oak, alligator juniper, white fir, Douglas-fir, Arizona cypress, border pinyon pine, Arizona madrone, and Texas madrone. Migrants may be found in lower elevations such as deserts, but they gravitate to moister, greener environments such as streambeds, oases, and backyards with gardens. The small number of birds that winter in the United States appear to be tied to feeding stations. In Mexico, nonbreeding birds appear in all sorts of habitats, from tropical deciduous forests at sea level to pine forests near treeline.

Food

Blue-throated Mountain-gems consume floral nectar, insects, and spiders. They rely heavily on invertebrate prey during the dry season, when flowers are scarce or absent. Mountain-gems capture insects in flight or glean them from vegetation or branches, sometimes even from spiderwebs or sapsucker wells. In especially productive areas for insects, they hunt from a favored perch or sometimes hover over water and chase insects. In May, new growth in conifers holds many insects, and mountain-gems often feed heavily on these, moving from tip to tip among the branches to glean prey. Prey include small spiders, harvestmen, aphids, flies, bugs, beetles, and wasps. Like most other hummingbirds, they hover at flowers (and feeders) and insert the long bill to drink nectar. They feed most heavily in the morning and late afternoon, resting during the heat of midday. In Arizona, they feed on bearded penstemon, cardinal monkeyflower, Texas betony, Lemmon’s sage, mountain sage, Harvard agave, Parry's agave, Palmer's agave, desert honeysuckle, golden columbine, twinberry, tree tobacco, New Mexican locust, Arizona thistle, coral bells, pointleaf manzanita, Arizona madrone, and various species of gilia (genus Ipomopsis). They also forage at flowers planted in gardens.

Nesting

Nest Placement

Females build nests on tree branches and rock ledges as well as houses, sheds, bridges, and other artificial supports. Nests are at least 6 feet off the ground and may be built on top of older nests and even nests of other species.

Nest Description

The female builds the nest. The outside of the nest is about 2 inches wide and 3–10 inches high (new nests may be built atop older ones). The inside cup measures 1–2 inches wide and 0.6–1.3 inches deep. Nests are held together with spider silk, plant fibers, animal hair, feathers, and even spider egg sacs and cocoons on the interior; and mosses, bark, and other plant matter on the exterior. Nests in drier areas may contain little or no moss and are not as well camouflaged. Unlike other hummingbirds, mountain-gems do not use lichens in their nests. Females may reuse materials from old nests when building new ones.

Nesting Facts

Behavior

Male Blue-throated Mountain-gems are avid and active in their courtship, although they don’t have a flight display as many other hummingbirds do. Instead, they sing and flash their blue gorget and the white corners of their tails; these displays may last for several days. Males sing a complex and variable song, usually from a perch, to mark territory, warn other males, and attract females. This song is quite soft, unlike the usual series of chip notes that males produce, and some have termed it a “whisper song.” Females attracted to a male sometimes give a sharp series of calls, especially when chased by males, and they also—remarkably—perch or fly very close to singing males and begin singing as well, a song similar to the male song. This duetting is unknown in other hummingbirds of the United States. After several days of courtship, males mate with females but provide no additional help with breeding activities. Females build the nest, incubate the eggs, defend the nest area, and raise the young. Males are territorial and aggressive toward other hummingbirds during the breeding season, often chasing away rivals for females or for food, sometimes attacking them with the large bill. To threaten other hummingbirds, males expand the plumage and fan and flick the large tail, making them appear quite large. Females are less aggressive but usually drive away other hummingbirds when feeding. Territory sizes have been measured in Mexico at 0.1 to 0.2 acres. Young males may attempt to establish territories shortly after fledging.

The sexes remain apart except during the brief period of courtship, and there is no evidence of pair bonds. As flowers become less prevalent in autumn, and the dry season begins, Blue-throated Mountain-gems migrate southward into Mexico, passing through deserts to winter mostly in mountains farther south, though some appear in coastal lowlands during winter.

Conservation

Blue-throated Mountain-gems are numerous in Mexico but they have a very limited range in the United States. Partners in Flight estimates a global breeding population of 2 million birds, with fewer than 2,000 of those in the United States. The species is a 12 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Although they adapt to some modifications of their habitat, including very low-density human settlement, the patchiness of their favored habitats makes them vulnerable to habitat loss, including logging, grazing, mining, water diversion, and the introduction of exotic plants.

Credits

Chai, P. and D. Millard. (1997). Flight and size constraints: hovering performance of large hummingbirds under maximal loading. Journal of Experimental Biology 200:2757-2763.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Rosenberg, K. V., J. A. Kennedy, R. Dettmers, R. P. Ford, D. Reynolds, J. D. Alexander, C. J. Beardmore, P. J. Blancher, R. E. Bogart, G. S. Butcher, A. F. Camfield, A. Couturier, D. W. Demarest, W. E. Easton, J. J. Giocomo, R. H. Keller, A. E. Mini, A. O. Panjabi, D. N. Pashley, T. D. Rich, J. M. Ruth, H. Stabins, J. Stanton, and T. Will (2016). Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

Williamson, Sheri L. (2000). Blue-throated Hummingbird (Lampornis clemenciae), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

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