Rück's blue flycatcher is a passerine bird in the Old World flycatcher family Muscicapidae. It is known from only four specimens and is endemic to a small area in northeast Sumatra, Indonesia, inhabiting primary lowland forest. Although all specimens share common characteristics, such as a black bill, brown iris, and black feet, two of the collected specimens show some physical discrepancy with the other two. They were initially described as Cyornis vanheysti before being accepted as specimens of C. ruckii. Rück's blue flycatcher has also been compared to other species of Cyornis.
Region
Sumatra, Indonesia
Typical Environment
The species is presumed restricted to primary lowland rainforest in northeastern Sumatra. It likely prefers dense, shaded understorey with scattered perches for sallying, especially near streams and in mature dipterocarp forest. Records suggest association with undisturbed forest rather than secondary growth or plantations. Given the paucity of observations, its precise range, microhabitat preferences, and tolerance of disturbance remain poorly known.
Altitude Range
0–300 m
Climate Zone
Tropical
Ease of Keeping
Beginner friendly: 1/5
Rück's blue flycatcher is known from only four historical specimens and is endemic to northeastern Sumatra, Indonesia. It was once split as Cyornis vanheysti, but those specimens are now considered within C. ruckii, though some plumage discrepancies persist. It likely inhabits intact lowland primary forest and may be highly elusive, which, together with habitat loss, explains the lack of recent records.
Temperament
shy and retiring
Flight Pattern
short rapid wingbeats
Social Behavior
Likely occurs singly or in pairs within territories in dense lowland forest. Nesting biology is unconfirmed but, by analogy with congeners, it may nest in cavities or sheltered sites close to the ground. Pair bonds are probably seasonal, with both sexes involved in care.
Migratory Pattern
Resident
Song Description
The vocalizations are poorly known. By comparison with related Cyornis, the song is expected to be a soft series of thin, whistled phrases and high-pitched notes, with a sharp ticking call when alarmed.
