It shares the genus Surniculus with the Philippine Drongo-cuckoo Surniculus velutinus. This is sometimes treated as a subspecies of S. lugubris, but can be separated as a species on the basis of vocalization and juvenile plumage.
Some recent work suggests that the species may need to be split into two based on call and morphological differences:
- Square-tailed Drongo-Cuckoo (Surniculus lugubris including brachyurus, musschenbroeki. It has white bars on the vent and outer undertail feathers. The tail is notched with slightly flared tips. In flight, a white wing-stripe is visible from below. It occurs naturally in South East Asia and is a summer visitor to the Himalayas from Kashmir to eastern Bangladesh. The calls are series of piercing sharp whistles rising in pitch but shrill and choppily delivered.
- Fork-tailed Drongo-Cuckoo (Surniculus dicruroides) – It has a deeply forked tail often having a white spot on the back of the head. The race is Sri Lanka stewarti has a shallower fork. Found resident mainly in peninsular India in hill forests although some specimens are known from the Himalayan foothills. They are said to brood parasites on the Dark-fronted Babbler. The song has been described as a series of 5 or 6 whistling “pip-pip-pip-pip-pip-” notes rising in pitch with each “pip”.