middle, and grayish olive on the outer half, with a dark green spot. The sides of the throat are whiter than in the male. The extent of the dusky color in the throat varies between individuals. The flanks, belly, breast, and undertail coverts are grayish buff with occasional brighter olive green feathers, as are the ventral regions of the tail. The tail has white patches, the size and shape of which vary between individuals. The flight feathers of the tail are dusky bluish green. In both sexes, the beak is black, with yellowish tomia. A holotype specimen weighed 8.15 g. Males of the species may be distinguished from congeners by the presence of the ultramarine throat, emerald green head and upperparts with bluish-green feather tips, and emerald green tips to the throat feathers. Females may be distinguished by the presence of a dusky-gray chin and upper throat in contrast to a whitish lower throat, and emerald green head and upperparts with bluish green feather tips on the head and a bluish green shine on the body. The males are most similar to those of the green-headed hillstar (O. stolzmanni) and the Ecuadorian hillstar (O. chimborazo); they are differentiated most clearly by the green throat patch in the green-headed hillstar, and the purple hood in the Ecuadorian hillstar. The vocalizations of the blue-throated hillstar are similar to those of its congeners; they are highly variable, and include rapid titters of rising and falling frequency, and single noted calls consisting of an "up–down stroke". Habitat and ecology The preferred habitat of the blue-throated hillstar is grassland with patches of shrubs in the Andean paramo. In the region that the type specimen was collected, the shrubs were dominated by Chuquiraga. The terrain in which it was found included hilly regions, steep terrain, rocky outcrops, and stream banks. O. cyanolaemus was observed to feed by clinging to branches sideways or upside down, or by perching next to flowers. It was observed feeding most frequently from Chuquiraga jussieui, and also from Macleania rupestris and Lleresia hypoleuca. Collected males were also found to have eaten flies. Some females were once observed making aerial sallies after swarming flies. Blue-throated hillstars were frequently observed being chased away from perches by Shining Sunbeams (Aglaeactis cupripenni). Aggressive interactions were also seen between it and the Viridian metaltail (Metallura williami). Distribution and conservation The species is endemic to an area of