Dark-rumped Swift Apus acuticauda Scientific name definitions

One of the most poorly known, and probably rarest, swifts in Asia, the Dark-rumped Swift was once considered a subspecies of the Pacific Swift Apus pacificus and molecular work confirms a close relationship between them. Definite breeding locations are few but include sites in eastern Bhutan (possibly fewer than ten pairs) and northeast India (perhaps including southern Assam and Nagaland), while it may also occur in Myanmar and the type specimen of the species is from Nepal. Records from northwest Thailand are exclusively in winter, between January and March, and the same is also true of sightings in Yunnan, in southwest China, although it has been suggested that the Thai birds might represent a separate taxon, but confirmation of this will surely necessitate specimens and further research. Dark-rumped Swift is typically observed around deep valleys cloaked in subtropical forest, with waterfalls and cliffs, where it nests between February or March until June in colonies, but it has also been observed feeding over farmland with some trees. On present evidence, the overall population is considered to number no more than 700 mature individuals, and the species is considered Vulnerable by BirdLife International.

16–17 cm (1 Rasmussen, P. C., and J. C. Anderton (2005). Birds of South Asia: the Ripley Guide. Lynx Edicions, Barcelona, Spain. Close ). Large swift with rakish structure  very like A. pacificus, but lacks white rump; outer tail slighter less thickset as outer rectrices strongly emarginated and tail shape overall is more reminiscent of A. caffer (2 Chantler, P. (2005). Dark-rumped Swifts: notes on their breeding plumage and how to see them. BirdingASIA. 4: 39–40. Close ). Upperparts black  ; underparts heavily marked with broad white fringes  , although appearance of pale belly may be due to wear (2 Chantler, P. (2005). Dark-rumped Swifts: notes on their breeding plumage and how to see them. BirdingASIA. 4: 39–40. Close ); throat-patch indistinct, more heavily streaked and probably averaging darker than in A. pacificus, which generally also lacks solid black undertail-coverts of present species (1 Rasmussen, P. C., and J. C. Anderton (2005). Birds of South Asia: the Ripley Guide. Lynx Edicions, Barcelona, Spain. Close ). Compared to A. apus, blacker above with deeper tail-fork, lacks pale areas on face, and has overall longer tail (1 Rasmussen, P. C., and J. C. Anderton (2005). Birds of South Asia: the Ripley Guide. Lynx Edicions, Barcelona, Spain. Close ). Juvenile has narrow white fringing to upperparts feathers and to tips of remiges (1 Rasmussen, P. C., and J. C. Anderton (2005). Birds of South Asia: the Ripley Guide. Lynx Edicions, Barcelona, Spain. Close ).

Breeds with certainty in E Buthan (4 Spierenburg, P. (2005). Birds in Bhutan. Status and Distribution. Oriental Bird Club, Bedford, UK. Close ) and around Cherrapunji and Lilancote, in Khasi Hills (NE India); thought to breed also in Lushai Hills, in Mizoram (extreme S Assam), and Nagaland (5 Ahmed, M.F., Das, A. and Meyase, V. (2007). Khasi Hills Swift Apus acuticauda: first record from Nagaland and Manipur, north-east India. J. Bombay Nat. Hist. Soc. 104(1): 87–88. Close ); may occur in Myanmar and (one specimen) Nepal. In Thailand, to date known only from winter records from NW; recorded also in S China (Yunnan).

Deep gulleys, often with waterfalls, and cliffs in the very wet Khasi Hills. Breeds at c. 400 m in Bhutan, where observed feeding over farmland with scattered trees, as well as subtropical forest (6 Bishop, K.D. (1999). Preliminary notes on some birds in Bhutan. Forktail. 15: 87–91. Close ), and birds wander up to at least 1400 m (7 Spierenburg, P. (2005). Birds in Bhutan: Status and Distribution. Oriental Bird Club, Bedford, UK. Close ), while species has been recorded between 200 m and 2470 m in India.

Winter records from NW Thailand and Yunnan (SW China) indicate short-distance migration, although birds concerned may possibly represent unknown populations. Myanmar records too few to indicate pattern to occurrence, although speculated to be resident there; most recent sighting, regarded as unconfirmed, was in winter (Dec) (8 Bezuijen, M.R., Eaton, J.A., Gidean, Hutchinson, R.O. and Rheindt, F.R. (2010). Recent and historical bird records for Kalaw, eastern Myanmar (Burma), between 1895 and 293939. Forktail. 26: 49–74. Close ). Found breeding in SE Bhutan (first recorded 1996), where certainly present in early Apr to mid May (7 Spierenburg, P. (2005). Birds in Bhutan: Status and Distribution. Oriental Bird Club, Bedford, UK. Close ) and Oct (9 Choudhury, A.U. (2006). Some new and interesting bird records from Bhutan. Indian Birds. 3(2): 51–53. Close ); few birders visit the area, except in spring, and species could be resident there. Not recorded from Andaman Is (19th century proved to be misidentified A. apus) (10 Chantler, P., and G. Driessens (2000). Swifts: A Guide to the Swifts and Treeswifts of the World. 2nd edition. Pica Press, Robertsbridge, UK. Close ), and some doubts surround origin of unique Nepalese record (the holotype). Often thought to be summer visitor to breeding zone, but records from throughout year in Indian portion of range.

Diet unknown, but has been observed foraging in small groups with Apus pacificus and Collocalia brevirostris (6 Bishop, K.D. (1999). Preliminary notes on some birds in Bhutan. Forktail. 15: 87–91. Close ), as well as with Hirundapus giganteus (11 Choudhury, A. (2016). Mizoram, north-east India: where to go and what you might see. BirdingASIA. 26: 99–106. Close ).

Calls around colonies often extremely high-pitched but cover broad frequency range, comprising rapid, thin trills that appear to waver in pitch (1 Rasmussen, P. C., and J. C. Anderton (2005). Birds of South Asia: the Ripley Guide. Lynx Edicions, Barcelona, Spain. Close ).

Season generally stated to be end Mar to end Apr, but perhaps more prolonged, Feb–Jun (1 Rasmussen, P. C., and J. C. Anderton (2005). Birds of South Asia: the Ripley Guide. Lynx Edicions, Barcelona, Spain. Close ). Colonial. Shallow cup-like nest of grass, moss (12 Ahmed, M.F., Das, A. and Meyase, V. (2007). Khasi Hills Swift Apus acuticauda: first record from Nagaland and Manipur, north-east India. Journal of the Bombay Natural History Society. 104(1): 87–88. Close ) and feathers agglutinated with saliva, on ledge in cliff fissure. Clutch 2–3, though four eggs have been recorded, size on average 26 mm × 16·3 mm (10 Chantler, P., and G. Driessens (2000). Swifts: A Guide to the Swifts and Treeswifts of the World. 2nd edition. Pica Press, Robertsbridge, UK. Close ). No further information (10 Chantler, P., and G. Driessens (2000). Swifts: A Guide to the Swifts and Treeswifts of the World. 2nd edition. Pica Press, Robertsbridge, UK. Close ).

VULNERABLE. Restricted-range species: present in Eastern Himalayas EBA. Overall population estimated at just 150–700 mature individuals. Apparently small population and very limited known range imply species at risk, though lack of recent information may mask true status. Bhutanese breeding population apparently tiny (< 10 pairs), but apparently stable and no known threats (7 Spierenburg, P. (2005). Birds in Bhutan: Status and Distribution. Oriental Bird Club, Bedford, UK. Close ). In NE India, one presumed breeding site lies within Blue Mountain National Park, Mizoram, with records in same state from Lengteng Wildlife Sanctuary (11 Choudhury, A. (2016). Mizoram, north-east India: where to go and what you might see. BirdingASIA. 26: 99–106. Close ), and has recently been discovered breeding in Khonoma Nature Conservation and Tragopan Sanctuary, Nagaland/Manipur (12 Ahmed, M.F., Das, A. and Meyase, V. (2007). Khasi Hills Swift Apus acuticauda: first record from Nagaland and Manipur, north-east India. Journal of the Bombay Natural History Society. 104(1): 87–88. Close ). Extensive research and survey work required.