Small hummingbird with an exceptionally long tail. Green overall with a fairly short, slightly decurved bill. The male’s long tail is striking. Sexes similar but females are more spotted below and have a shorter tail. Could be confused with Long-tailed Sylph, but the trainbearer occurs in dry, scrubby, open habitats, not in forests. Compare with very similar Green-tailed Trainbearer; Black-tailed has a longer, more decurved bill, a longer tail that usually looks slightly curved, and is somewhat duller green. Occurs from Colombia to Peru, from around 2,500 to 3,800 m. Occasionally visits feeders, but more often seen feeding at flowering shrubs.