Waterfall Swift Hydrochous gigas Scientific name definitions

Also referred to as the Giant Swiftlet or Waterfall Swiftlet, this species’ large size and differences in breeding biology have led to its being separated in a genus apart, although not all taxonomists favour such an arrangement. This comparatively large swift has a deeply forked tail (albeit usually held closed) and generally uniform plumage (darker on the upperparts), but is not capable of echolocation. Considered Near Threatened by BirdLife International, the generally rare and local Waterfall Swift is endemic to the Sundaic region, where it is associated with waterfalls in primary lower montane and upper montane forest in Peninsular Malaysia, western and northern Sumatra, and West Java, with a few, widely scattered sight-only records across the northern half of Borneo (in Brunei, Sabah and Sarawak); it is presumably resident on the latter island.

A fairly large swift , appearing rather more like some of the Apodini swifts than the swiftlets, with deeply forked tail; uniformly dark brown above, slightly paler but still very uniform below. Not capable of echolocation (1 Medway, Lord and Wells, D.R. (1969). Dark orientation by the Giant Swiftlet Collocalia gigas. Ibis 111(4):609–611. Close ).

Considerably larger than all sympatric swiftlets, with a silhouette closer to that of House Swift (Apus nipalensis), broader and more triangular wings than other swiftlets, and has a bulkier body. Flight is described as being very smooth and direct on deep wingbeats, with the wings held only just below the horizontal (unlike swiftlets), and also lacks the unsteady rocking flight behavior of swiftlets. Note that although Waterfall Swiftlet has an obvious tail fork, the tail is often tightly closed for long periods in flight.

Nestling

The following is based entirely on Becking (2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close ). Hatchling is naked and blind. A well-developed whitish egg tooth is conspicuous at the distal upper ridge of the maxilla of the pinkish bill. The mandible protrudes somewhat beyond the maxilla due to a second egg tooth at the distal end of the mandible. The skin is pinkish, with a very slight plumbeous or grayish tinge, darker on the head, back, and wings. The pinkish feet are soft and rather large. Newly hatched chicks weighed c. 2–3 g and have a body length of c. 3.5 cm. At age 4–8 days, the chick develops slightly darker plumbeous feather tracts below the epidermis, one dorsal (spinal tract), and one on each side (femoral tract). Subsequently, the plumbeous-gray back and head become darker, and the pinkish bill acquires a blackish tip and darker upper rim. When 6–7 days old, the chick is c. 5 cm in length, and weighs c. 9.3 g. At 10–15 days, a ‘downy’ grayish-black semiplume covering sprouts on the back, giving the chick what looks like a coat of down. The first wing and tail feathers appear, still enclosed by their sheaths. The eyes first open at this age. At c. 17–22 days, the semiplumes are still prominent, and growth of the primaries and secondaries, followed by the greater coverts, is rather rapid. As these feathers are still in sheath, the chick acquires a pin-cushion-like appearance, and later the secondaries and upperwing-coverts start to open their vanes at the tips, whilst the primaries are still within their sheaths. The plumulaceous bases of these new feathers bear blackish-gray barbs identical to the initial semiplumes, but the closed vane is buffish yellow, and the gray semiplume-like endings have fine yellowish tips, affording a somewhat variegated appearance. A second wave of largely plumulaceous feathers arising from other follicles is exceptional (being unknown in all other swifts), and conflicts with any molt system known. At c. 25–45 days the chick is are covered with sooty gray-brown contour feathers, paler on the underside and darker on the upperside, with extensive white at their bases, particularly on the back, belly, and flanks, giving the nestling a somewhat spotted appearance. Completely white small underlying feathers also occur on the back and belly, but apparently only very few semiplumes under these first contour feathers. It is noteworthy that Waterfall Swift nestlings at this age lack the pale grayish fringes to the primaries, secondaries, and other contour feathers that are well known in older nestlings or juveniles of Apus, and also present in some Cypseloidinae (3 Marín, M., and F. G. Stiles (1992). On the biology of five species of swifts (Apodidae, Cypseloidinae) in Costa Rica. Proceedings of the Western Foundation of Vertebrate Zoology 4(5):286–351. Close ).

Juvenile/First-winter

Differs from adult by less prominent gray-white fringes to the undertail-coverts, but more pronounced white on the concealed feather barbs of the body feathers. First-year birds differ in that the central pair of rectrices have asymmetrical outer and inner webs at the tips (these are symmetrical in adults).

Adult

Upper head black-brown and slightly glossed, and entire upperparts are similar, showing no contrast with the head; remiges and rectrices are also black-brown. Forehead and narrow line of feathers above the eye have grayer fringes, appearing contrastingly paler, but only slightly so. Black eye patch, with whiter bases to the feathers. Ear-coverts similar, but become progressively paler away from the crown, and the entire throat is mid-brown to gray-brown, and appears slightly mottled. Underparts are fairly uniform mid-brown, although the throat usually appears marginally paler; the undertail-coverts have distinct grayish-white fringes. Underwing shows some contrast between the dark glossy gray remiges and dark gray coverts, especially the more blackish lesser coverts, and the leading edge of the wing appears slightly paler, and gray-fringed. Sexes similar.

All data from Somadikarta (4 Somadikarta, S. (1968). The Giant Swiftlet Collocalia gigas Hartert and Butler. Auk 85(4):549–559. Close ). Primaries are molted descendantly, from the innermost to the outermost, with p2 usually shed when p1 is in large pin and the rest are shed sequentially when the adjacent one is half-grown to full length, while usually no more than two primaries are growing simultaneously. The secondaries are replaced starting with s1 (the outermost) followed by the seventh (innermost), then the second, third, fourth, fifth, and sixth centripetally, with s6 shed at the same time as p9 is full or p1 is in pin. Tail molt progresses centripetally, starting with the outermost pair of rectrices, concurrent with the growth of p7 or p8, rarely earlier. Probably the wing and tail feathers are not molted during the first year of life; at least some, but not all, juvenile body feathers are in molt when pp5–10 are growing. Whereas males commence wing molt in the last week of December, females do so one month later, and both complete feather replacement between late August and mid September, thereby complementing the breeding cycle; no females, and just one male, was in molt during the nesting season. Five live birds trapped in Peninsular Malaysia in October–November showed no evidence of molt (5 Wells, D. R. (1999). The Birds of the Thai-Malay Peninsula. Volume 1. Non-passerines. Academic Press, London, UK. Close ).

Adult has all of the bare parts blackish (5 Wells, D. R. (1999). The Birds of the Thai-Malay Peninsula. Volume 1. Non-passerines. Academic Press, London, UK. Close ).

Linear Measurements

Overall length 16 cm.

Linear measurements (in mm, means and sample sizes in parentheses, all data from Somadikarta 4 Somadikarta, S. (1968). The Giant Swiftlet Collocalia gigas Hartert and Butler. Auk 85(4):549–559. Close ):

Mass

Male 37 g, female 35–39 g (4 Somadikarta, S. (1968). The Giant Swiftlet Collocalia gigas Hartert and Butler. Auk 85(4):549–559. Close ), unsexed 36.5–45.9 g (5 Wells, D. R. (1999). The Birds of the Thai-Malay Peninsula. Volume 1. Non-passerines. Academic Press, London, UK. Close ).

Currently treated as the sole member of the genus Hydrochous, which is perhaps closest to Aerodramus, and both are commonly merged into Collocalia.

None.

Monotypic.

Large size and differences in breeding biology favour generic isolation of present species (6 Brooke, R. K. (1972). Generic limits in old world Apodidae and Hirundinidae. Bulletin of the British Ornithologists’ Club 92(2):53–57. Close , 7 Medway, Lord, and D. Pye (1977). Echolocation and the systematics of swiftlets. In Evolutionary Ecology (B. Stonehouse, and C. M. Perrins, Editors), Macmillan, London, UK. pp. 225–238. Close ), although some authors have regarded these differences as marginal and of doubtful taxonomic significance; others suggest that present species may not be closely related to the swiftlet genera (8 Brooke, R.K. (1970). Taxonomic and evolutionary notes on the subfamilies, tribes, genera and subgenera of the swifts (Aves: Apodidae). Durban Museum Novitates 9(2):13–24. Close , 9 King, B. (1987). The Waterfall Swift Hydrochous gigas. Bull. Brit. Orn. Club. 107(1):36–37. Close ). The ‘down-like’ semiplume nestling plumage of this species is absent in all Collocalia and Aerodramus species but does occur in the subfamily Cypseloidinae of the New World, presumably as a result of convergence (2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close ). DNA and other studies inconclusive (10 Lee, P. L. M., D. H. Clayton, R. Griffiths, and R. D. Price (1996). Does behaviour reflect phylogeny in swiftlets (Aves: Apodidae)? A test using cytochrome b mitochondrial DNA sequences. Proceedings of the National Academy of Sciences of the United States of America 93:7091–7096. Close , 11 Thomassen, H. A., A. T. Wiersema, M. A. G. de Bakker, P. de Knijff, E. Hetebrij, and G. D. E. Povel (2003). A new phylogeny of swiftlets (Aves: Apodidae) based on cytochrome-b DNA. Molecular Phylogenetics and Evolution 29(1):86–93. Close ); while one phylogenetic analysis indicated that present species and Three-toed Swiftlet (Aerodramus papuensis) are sister taxa (12 Price, J. J., K. P. Johnson, S. E. Bush, and D. H. Clayton (2005). Phylogenetic relationships of the Papuan Swiftlet Aerodramus papuensis and implications for the evolution of avian echolocation. Ibis 147(4):790–796. Close ), its precise taxonomic position remains to be determined (2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close , 13 Thomassen, H. A., R. J. den Tex, M. A. G. de Bakker, and G. D. E. Povel (2005). Phylogenetic relationships amongst swifts and swiftlets: a multi locus approach. Molecular Phylogenetics and Evolution 37(1):264–277. Close ).

Nothing known.

Mountainous areas of Peninsular Malaysia (14 Medway, L., and D. R. Wells (1976). The Birds of the Malay Peninsula. Volume 5. Conclusions and Survey of Every Species. Witherby & Penerbit University Malaya, London, UK & Kuala Lumpur, Malaysia. Close , 5 Wells, D. R. (1999). The Birds of the Thai-Malay Peninsula. Volume 1. Non-passerines. Academic Press, London, UK. Close ), Sumatra (15 van Marle, J. G., and K. H. Voous (1988). The Birds of Sumatra. An Annotated Check-list. B.O.U. Check-list 10. British Ornithologists’ Union, Tring, UK. Close ) and West Java (16 Bartels, M. (1915). Zur Ornis Java. Verh. orn. Ges. Bayern 12:199–200. Close ); few records from Borneo (17 Smythies, B. E. (1957). An annotated checklist of the birds of Borneo. Sarawak Museum Journal (New Series) 7(9):523–818. Close , 18 Smythies, B. E. (1981). The Birds of Borneo. Third edition. The Sabah Society and the Malayan Nature Society, Kuala Lumpur, Malaysia. Close , 19 Mann, C. F. (2008). The Birds of Borneo. An Annotated Checklist. B.O.U. Checklist 23. British Ornithologists’ Union and British Ornithologists’ Club, Peterborough, UK. Close ).

Typically found over mountainous rainforest in areas of waterfalls; known from c. 800 to 1,500 m in Malay Peninsula (5 Wells, D. R. (1999). The Birds of the Thai-Malay Peninsula. Volume 1. Non-passerines. Academic Press, London, UK. Close ), c. 440 m in Sumatra and c. 300–1,500 m in West Java.

Believed to be resident, although the available data are equivocal; virtually all records in Peninsular Malaysia are dated October–November and March (5 Wells, D. R. (1999). The Birds of the Thai-Malay Peninsula. Volume 1. Non-passerines. Academic Press, London, UK. Close ). Recorded at night from Fraser’s Hill (20 Wells, D. R. (1992). Night migration at Fraser’s Hill, Peninsular Malaysia. Bulletin of the Oriental Bird Club 16:21–25. Close ), western Peninsular Malaysia, and on islands off northern Borneo.

Analyses of stomach contents from West Java show prey variable, presumably depending on availability: one stomach contained mainly flying ants, lesser numbers of Diptera, including sizeable tipulid, a small beetle and a small bug (4 Somadikarta, S. (1968). The Giant Swiftlet Collocalia gigas Hartert and Butler. Auk 85(4):549–559. Close ). Others recorded predominance of Diptera (4 Somadikarta, S. (1968). The Giant Swiftlet Collocalia gigas Hartert and Butler. Auk 85(4):549–559. Close ). However, species is believed to have strong predilection for winged termites, at least during the breeding season (2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close ). Gregarious, often with Brown-backed Needletail (Hirundapus giganteus) and to lesser extent Cave Swiftlet (Collocalia linchi) on Java (4 Somadikarta, S. (1968). The Giant Swiftlet Collocalia gigas Hartert and Butler. Auk 85(4):549–559. Close ). Though lacks ability to echolocate, has acute poor-light vision and may be mainly a crepuscular feeder (21 Chantler, P. and Driessens, G. (2000). Swifts. A Guide to the Swifts and Treeswifts of the World. 2nd edition. Pica Press, Robertsbridge, UK. Close ). Data suggest this species more likely to be seen foraging during day on Java in rainy season, October–March.

Poorly documented, and reported to be usually silent (22 Myers, S. (2016). Birds of Borneo. Second edition. Christopher Helm, London, UK. Close ); described as a sharp wickering or loud twittering, readily audible above the roar of the waterfall and somewhat similar to the voice of House Swift (Apus nipalensis) (9 King, B. (1987). The Waterfall Swift Hydrochous gigas. Bull. Brit. Orn. Club. 107(1):36–37. Close ). A bird handled at night in Peninsular Malaysia uttered a brief, Apus-like chittering (5 Wells, D. R. (1999). The Birds of the Thai-Malay Peninsula. Volume 1. Non-passerines. Academic Press, London, UK. Close ).

Recorded October–March in West Java (16 Bartels, M. (1915). Zur Ornis Java. Verh. orn. Ges. Bayern 12:199–200. Close , 4 Somadikarta, S. (1968). The Giant Swiftlet Collocalia gigas Hartert and Butler. Auk 85(4):549–559. Close , 23 Becking, J.-H. (1971). The breeding of Collocalia gigas. Ibis 113(2):330–334. Close , 2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close ); egg taken late Apr in Peninsular Malaysia (24 Allen, F. G. H. (1961). Further notes on breeding birds of Fraser’s Hill. Malayan Nature Journal 15:45–47. Close , 23 Becking, J.-H. (1971). The breeding of Collocalia gigas. Ibis 113(2):330–334. Close ). Nests are always associated with falling water, being usually placed singly or in small colonies of up to ten (especially 5–8) (25 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: I. Occurrence and nesting. Bull. Brit. Orn. Club 126(2):117–122. Close ), on ledges or in crevices behind or very close to waterfalls (16 Bartels, M. (1915). Zur Ornis Java. Verh. orn. Ges. Bayern 12:199–200. Close , 26 Hoogerwerf, A. (1949). De Avifauna van Tjibodas en Omgeving (Java). Koninklijke Plantentuin van Indonesië, Buitenzorg, Java. Close , 23 Becking, J.-H. (1971). The breeding of Collocalia gigas. Ibis 113(2):330–334. Close ), but perhaps 10–20% of nests are sited in nearby narrow gorges or ravines, where rapid streams or rivulets formed small cascades of water, here usually singly or in tiny groups of up to four (25 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: I. Occurrence and nesting. Bull. Brit. Orn. Club 126(2):117–122. Close ). Inter-nest distance is typically 3–15 m (25 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: I. Occurrence and nesting. Bull. Brit. Orn. Club 126(2):117–122. Close ). Nest is constructed mainly (90–95%) of liverworts (Mustigophora and Herberta spp.) with green fern fronds or whole ferns (Hymenophyllaceae and Asfdenium sp.) in the nest wall, collected by birds by pulling with beak while still in flight, and to lesser extent mosses (Aerobryopsis, Ectropothecium and Meteorium spp.) and aerial roots of epiphytes (Orchidaceae), agglutinated with feathers and saliva into a truncated cone and attached with same adhesive to rock substrate, on small ledge within spray of waterfall (23 Becking, J.-H. (1971). The breeding of Collocalia gigas. Ibis 113(2):330–334. Close ); 90–100 mm in diameter, 40–60 mm tall at the front but 10–30 mm at the back, and the egg chamber measures 60–70 mm in diameter and is just 10–15 mm deep (23 Becking, J.-H. (1971). The breeding of Collocalia gigas. Ibis 113(2):330–334. Close ). An earlier description (27 Hoogerwerf, A. (1950). De avifauna van Tjibodas en omgeving, inclusief het natuurmonument Tjibodas-Gn. Gede (West-Java). Limosa 23(1–2):1–158. (In Dutch.) Close ) of a nest as comprising mainly dark rootlets is erroneous (23 Becking, J.-H. (1971). The breeding of Collocalia gigas. Ibis 113(2):330–334. Close ). Same nests are typically occupied in consecutive seasons (25 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: I. Occurrence and nesting. Bull. Brit. Orn. Club 126(2):117–122. Close ), although whether by the same individuals is unknown. Clutch typically a single white egg (26 Hoogerwerf, A. (1949). De Avifauna van Tjibodas en Omgeving (Java). Koninklijke Plantentuin van Indonesië, Buitenzorg, Java. Close ), measuring 28.2 (26.0–31.5) × 18.1 (17.2–19.2) mm (28 Hellebrekers, W. P. J., and A. Hoogerwerf (1967). A further contribution to our zoological knowledge of the island of Java (Indonesia). Zoologische Verhandelingen Leiden 88:1–64. Close , 23 Becking, J.-H. (1971). The breeding of Collocalia gigas. Ibis 113(2):330–334. Close ). Replacement clutch is laid if first is lost (2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close ). Incubation and nestling periods appear to be unknown with certainty, but the latter is estimated at 48–55 days (2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close ). The hatchling is naked and blind, but has a well-developed whitish egg tooth on the distal upper ridge of the pinkish bill, while the lower mandible protrudes somewhat beyond the maxilla due to a second egg tooth at its tip; the skin is pinkish, with a very slight plumbeous or greyish tinge, darker on the head, back and wings; mass c. 2–3 g (2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close ). By 24–25 days, the chick is covered with sooty grey-brown contour feathers, paler on the underside and darker above, with extensive white at their bases, especially on the back, belly and flanks, while completely white small underlying feathers occur on the back and belly, but apparently only very few semiplumes under these first contour feathers; they lack lack the pale greyish fringes to the primaries, secondaries and other contour feathers well known in older nestlings or juveniles of Apus and some Cypseloidinae (2 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: II. Nestling plumage and phylogenetic relationships. Bull. Brit. Orn. Club 126(2):123–136. Close ).

No information (5 Wells, D. R. (1999). The Birds of the Thai-Malay Peninsula. Volume 1. Non-passerines. Academic Press, London, UK. Close ).

Not globally threatened. Currently considered Near Threatened. Restricted-range species: present in Sumatra and Peninsular Malaysia EBA and Java and Bali Forests EBA (29 Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wege (1998). Endemic Bird Areas of the World: Priorities for Biodiversity Conservation. BirdLife Conservation Series 7. BirdLife International, Cambridge, UK. Close ). Rare and local, though exact status unclear with few population counts; 60–80 together at well-known breeding site (Gunung-Gede/Pangrango National Park) in West Java, August 1985 (9 King, B. (1987). The Waterfall Swift Hydrochous gigas. Bull. Brit. Orn. Club. 107(1):36–37. Close , 30 Andrew, P. (1985). An annotated checklist of the birds of the Cibodas-Gunung Gede Nature Reserve. Kukila 2(1):10–28. Close ). Counts of up to eight at site near Gunung Kerinci, in Kerinci-Seblat National Park, south-central Sumatra (15 van Marle, J. G., and K. H. Voous (1988). The Birds of Sumatra. An Annotated Check-list. B.O.U. Check-list 10. British Ornithologists’ Union, Tring, UK. Close ). Said to be common around Mt Pangrango in early 20th century (15 van Marle, J. G., and K. H. Voous (1988). The Birds of Sumatra. An Annotated Check-list. B.O.U. Check-list 10. British Ornithologists’ Union, Tring, UK. Close ). May be more widespread in Sumatra than currently thought, as two records (groups of seven and eight individuals) from Gunung Leuser and record of two from Brestagi (15 van Marle, J. G., and K. H. Voous (1988). The Birds of Sumatra. An Annotated Check-list. B.O.U. Check-list 10. British Ornithologists’ Union, Tring, UK. Close ). Distribution and status in Borneo still poorly known, with the few records (all since 1950s) either involving local wanderers from a resident population, or visitors from elsewhere, occurring from lowlands to 1,800 m, in Brunei, Kalimantan, Sabah and Sarawak (31 Wilkinson, R., G. Dutson, B. Sheldon, Darjono, and Y. S. Noor (1991). The avifauna of Barito Ulu region, Central Kalimantan. Kukila 5(2):99–116. Close , 19 Mann, C. F. (2008). The Birds of Borneo. An Annotated Checklist. B.O.U. Checklist 23. British Ornithologists’ Union and British Ornithologists’ Club, Peterborough, UK. Close , 32 Fischer, J. H., N. S. Boyd, A. Maruly, A., A.-S. van der Kaaden, S. J. Husson, and J. Sihite (2016). An inventory of the avifauna of the Bukit Batikap Protection Forest, Central Kalimantan, Indonesia. Forktail 32:26–35. Close ); local people report that what is presumably this species breeds at a waterfall in Bukit Batikap Protection Forest, central Kalimantan (32 Fischer, J. H., N. S. Boyd, A. Maruly, A., A.-S. van der Kaaden, S. J. Husson, and J. Sihite (2016). An inventory of the avifauna of the Bukit Batikap Protection Forest, Central Kalimantan, Indonesia. Forktail 32:26–35. Close ), suggesting that Hydrochous gigas is indeed resident on Borneo. Recorded over Panti Forest Reserve, Johor Province, Malaysia, in November 1996 (33 Robson, C.R. (1997). From the field. Malaysia. Bulletin of the Oriental Bird Club 25:67. Close ). Deforestation in vicinity of nest sites, as well as human disturbance, can ultimately cause colonies to be abandoned, even if the waterfall or ravine itself remains suitable (25 Becking, J.-H. (2006). Notes on Waterfall Swift Hydrochous gigas: I. Occurrence and nesting. Bull. Brit. Orn. Club 126(2):117–122. Close ).