Slender-tailed Woodstar

This minuscule representative of the Trochilidae family is distinguished by its delicate physique, pronounced sexual dimorphism, and remarkably slender tail feathers. Adults typically measure between 7 and 9 centimeters in total length and weigh a mere 2 to 3 grams. The male exhibits a shimmering metallic olive-green dorsal plumage, highlighted by a striking, iridescent amethyst-pink to violet gorget on the throat, bordered below by an inconspicuous whitish pectoral band. Its underparts are mostly grayish-green. The male´s tail is exceptionally long, deeply forked, and features extremely thin, thread-like outer rectrices of a dark coloration. Conversely, the female lacks the brilliant throat patch, showing instead a warm pale cinnamon or buffy throat and breast, green upperparts, and a shorter, rounded tail tipped with white and cinnamon. Both sexes possess a short, straight, and black bill that is proportionate to their small head.

Geographical distribution: It is primarily restricted to the inter-Andean valleys and the eastern slopes of the Andes, extending from central Bolivia (including the departments of Cochabamba, Santa Cruz, Chuquisaca, and Tarija) southward to northwestern Argentina (inhabiting the provinces of Jujuy, Salta, Tucumán, and Catamarca). Its distribution is somewhat disjunct but closely tied to specific sub-Andean elevation zones.

Habitat: It primarily frequents semi-arid environments, temperate valleys, dry montane forest edges, xerophytic scrublands, and open woodlands dominated by Prosopis or Acacia species. It is most commonly recorded at elevations ranging from 1,000 to 3,000 meters above sea level, showing a high adaptability to degraded secondary scrublands and ecotones between Andean dry forests and the wetter yungas.

Feeding: It is essentially nectarivorous, complementing its diet with small soft-bodied arthropods. It feeds on a diverse range of flowering plants with short tubular corollas, showing a preference for species within the Fabaceae, Solanaceae, and Loranthaceae families. To fulfill its protein requirements, it engages in aerial hawking to capture tiny flying insects and gleans small spiders directly from the foliage and branches.

Behavior: It exhibits an incredibly rapid, agile, and darting flight pattern, which often resembles that of a large insect due to its diminutive size and high wingbeat frequency. Males are territorial and defend rich floral patches against rivals and other hummingbirds, singing from exposed perches atop low shrubs with high-pitched, metallic squeaks. During the breeding season, males perform steep aerial displays to court females.

Nesting: Breeding activity occurs during the wet season, which corresponds with peak floral availability from late spring through the austral summer. The female is solely responsible for nest construction, incubation, and provisioning. The nest is a compact, cup-shaped structure meticulously woven from fine plant fibers, moss, and lichens, bound together with spider silk to allow the nest to stretch as the chicks develop. It is typically built on thin, sheltered branches of low shrubs. The clutch size consists of two pure white eggs, incubated for a period of 14 to 16 days.

Conservation status: It is currently classified as Least Concern (LC) on the IUCN Red List. Although its global population of Microstilbon burmeisteri is not considered threatened, local populations face moderate pressure from habitat loss, degradation, and fragmentation caused by agricultural expansion and overgrazing in the fragile dry forest ecosystems of the Andes.