White-tailed Goldenthroat

This elegant taxon displays a highly specialized morphology adapted to the open and humid landscapes of South America. It is a medium-sized hummingbird, measuring between 9.5 and 11 centimeters in length and weighing around 4.5 grams. Its most prominent diagnostic feature is a long, decurved bill, which features a black upper mandible and a contrasting pinkish lower mandible with a dark tip. The dorsal plumage is a shimmering golden-green or bronze-green. Adult males boast a brilliant, metallic golden-green underparts, whereas females present a lighter, whitish-buff throat and breast speckled with green. The face of Polytmus guainumbi features a highly visible white postocular stripe paired with a dark auricular patch. The slightly rounded tail displays bronze-green central feathers, while the outer feathers are tipped with broad, conspicuous white bands, a key diagnostic field mark especially visible during flight.

Geographical distribution: It is widely distributed throughout the eastern region of South America. Its geographic range extends from northern South America in Colombia, Venezuela, Trinidad and Tobago, Guyana, Suriname, and French Guiana, southward through vast portions of Brazil (primarily excluding the heavily forested core of the Amazon basin). Its presence continues through eastern Bolivia and Paraguay, reaching its southern limit in northeastern Argentina, specifically in the provinces of Formosa, Chaco, Corrientes, and Misiones.

Habitat: This species primarily occupies open and semi-open biomes with high humidity and abundant water sources. It is highly characteristic of wet savannas, seasonally flooded grasslands, marsh borders, Cerrado formations, riparian shrublands, and agricultural landscapes with scattered low bushes. It is predominantly found in lowland areas, generally staying below 1000 meters above sea level, strictly avoiding the interior of dense, closed-canopy primary forests.

Feeding: The diet is highly nectarivorous, supplemented by the intake of small invertebrates. It extracts high-energy nectar from a diverse array of flowering plants, showing a marked preference for species within the Fabaceae, Rubiaceae, Bromeliaceae, and Malvaceae families. Its curved bill is perfectly adapted to access tubular corollas. To fulfill its protein requirements, it captures tiny insects mid-air using aerial hawking maneuvers and gleans small arthropods directly from foliage surfaces.

Behavior: Highly active and aggressively territorial, it is known for its energetic defense of rich nectar sources. It is frequently observed perching on exposed, low-lying twigs of bushes to monitor its feeding territory. It performs complex, agile aerial displays to ward off both conspecifics and other hummingbird species. Its vocalization consists of a repetitive, high-pitched metallic chatter, most commonly heard during the early morning hours.

Nesting: The breeding biology of this hummingbird involves the construction of a neat, cup-shaped nest. The female alone gathers materials, utilizing soft plant fibers, seed down, and spider webs to bind the structure, decorating the outer walls with lichens for camouflage. The nest is typically placed low, between 0.5 and 1.5 meters above the ground or water surface, securely attached to the vertical forks of thin shrubs in swampy areas. The female lays a clutch of two white, elliptical eggs. Incubation lasts between 14 and 15 days and is performed exclusively by the female. She also assumes sole responsibility for brooding and feeding the chicks via regurgitation until they fledge, which occurs at 20 to 22 days of age.

Conservation status: It is currently classified as Least Concern (LC) on the IUCN Red List. Although its global population is considered stable and its geographical range is exceptionally large, localized threats persist. The drainage of wetlands, conversion of natural savannas into intensive agricultural land, and cattle ranching continue to alter and fragment its preferred habitats.