Mascarene Swiftlet Aerodramus francicus Scientific name definitions

A typical small swift, with very dark greyish brown plumage relieved only by paler underparts and especially rump, the Mascarene Swiftlet is endemic to the western Indian Ocean islands of Mauritius and Reunion, where it nests colonially in caves. Old reports of this species, little more than rumours, from Madagascar in the late 19th century are no longer considered to be acceptable, and presumably referred to the shorter-tailed Madagascar Spinetail (Zoonavena grandidieri). This species is currently considered Near Threatened by BirdLife International, with its population of 6,000‒15,000 mature individuals being limited by the relative paucity of suitable nest sites. It is generally rather common, perhaps even locally abundant on both islands, but on Reunion, where numbers appear to be unquestionably smaller, several of the species’ colonies are threatened by the actions of speleologists. Differences between the two populations, mooted for some years but never properly investigated, have very recently led to the proposal that two subspecies should be recognized.

Small swiftlet with forked tail; dark brown upperparts with whitish rump clearly paler, pale brown underparts. Species capable of echolocation.

Compared to similar but allopatric Seychelles Swiftlet (Aerodramus elaphrus), Mascarene Swiftlet has proportionately shorter wings and shorter bill, a narrower wing base (evident in flight) with secondaries clearly shorter than the tertials, and appears less hirundine-like. Also, Seychelles Swiftlet has a larger eye set within a deeply recessed loral mask, whereas Mascarene Swiftlet has a relatively small eye and shallow loral mask. Only real confusion species within the same distribution is Mascarene Martin (Phedina borbonica), which is larger, has shorter broader wings, and overall paler brown plumage. The present species has, in the past, been claimed to occur in Madagascar (1 Milne-Edwards, A., and A. Grandidier (1879). Histoire physique, naturelle et politique de Madagascar. Volume 12. Histoire naturelle des oiseaux. Tome 1. Imprimerie Nationale, Paris, France. Close ), where presence of Madagascar Spinetail (Zoonavena grandidieri) complicates matters, it being only slightly larger and longer-tailed than the present species, with more prominent black shaft-streaks below and, especially, on rump, and unlike Mascarene Swiftlet has very short spines on tips of tail feathers.

Juvenile

From Safford and Hawkins (2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ). Like adult, but tips of inner primaries and secondaries are finely fringed pale buff; plumage is usually fresh when adult is worn.

Adult

Based on type description of A. f. saffordi (3 Kirwan, G.M., H. Shirihai, and M. Schweizer (2018) A morphological revision of Mascarene Swiftlet Aerodramus francicus, with the description of a new subspecies from Reunion. Bulletin of the British Ornithologists’ Club 138(2):117–130. Close ). Very dusky above, and paler, slightly greyer below. Head basically shows four tones: the cap which is blacker and quite well demarcated reaching level with lowest part of eye; the lores which are even blacker; the paler greyish-brown ear-coverts and chin (slightly paler than the ear-coverts); with the throat being the palest part of the head. Upperparts: largely dusky brown, contrasting with ill-defined paler grey rump, with very few whitish bases and edges exposed; rectrices, remiges and some of the coverts and tertials are darkest part of wing, almost blackish brown, with very slight greenish gloss/iridescence. Underparts: lower throat to breast drab brown, or slightly darker, forming a very broad and somewhat diffuse breast-band, below which the remainder of the underparts (belly to undertail-coverts) become paler; especially from the mid-breast across the belly, shaft-streaks are very well pronounced and there are dark feather centres exposed between the lower throat and upper breast forming a broken mesial stripe. Underwing-coverts as top of head, but underside of remiges marginally paler. Sexes alike.

Almost nothing published; only details from Cheke (4 Cheke, A. S. (1987). The ecology of the smaller landbirds of Mauritius. In Studies of Mascarene Landbirds (Diamond, A. W., Editor), Cambridge University Press, Cambridge, UK. pp. 151–207. Close ). Molt takes 6–7 months (sometimes perhaps five months), overlapping with breeding and broadly synchronized within (but not between) colonies; at two adjacent colonies, feather replacement among adults commenced in October at one, but in November at the other.

Linear Measurements

Overall length 10.5 cm.

Linear measurements (in mm, means and sample sizes, where available, in parentheses, sexes combined):

Mass

A. f. francicus 7.8–13.9 g; A. f. saffordi 7.9–11.4 g (5 Cheke, A.S. and Jones, C.G. (1987). Measurements and weights of the surviving endemic birds of the Mascarenes and their eggs. Pp. 403–422 in: Diamond (1987). Close , 2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close , 3 Kirwan, G.M., H. Shirihai, and M. Schweizer (2018) A morphological revision of Mascarene Swiftlet Aerodramus francicus, with the description of a new subspecies from Reunion. Bulletin of the British Ornithologists’ Club 138(2):117–130. Close ).

Editor's Note: This article requires further editing work to merge existing content into the appropriate Subspecies sections. Please bear with us while this update takes place.

In the past, was treated as part of a composite species that also included Halmahera Swiftlet (A. infuscatus), Mountain Swiftlet (A. hirundinaceus), Australian Swiftlet (A. terraereginae), and White-rumped Swiftlet (A. spodiopygius) (6 Oberholser, H. C. (1906). A monograph of the genus Collocalia. Proceedings of the Academy of Natural Sciences of Philadelphia 58:177–212. Close , 7 Medway, Lord (1966). Field characters as a guide to the specific relations of swiftlets. Proceedings of the Linnean Society of London 177(2):151–172. Close , 8 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 , 9 Pratt, H. D. (1986). A review of the English and scientific nomenclature of cave swiftlets (Aerodramus). 'Elepaio. 46(11):119–125. Close ).

Differences between birds on Reunion and those on Mauritius suggest that two subspecies are involved (3 Kirwan, G.M., H. Shirihai, and M. Schweizer (2018) A morphological revision of Mascarene Swiftlet Aerodramus francicus, with the description of a new subspecies from Reunion. Bulletin of the British Ornithologists’ Club 138(2):117–130. Close ). See below.

Two subspecies recognized, one only recently described.

A. f. francicus (J. F. Gmelin, 1789)—Mauritius.

A. f. saffordi Kirwan, Shirihai and Schweizer, 2018—Reunion. Differs by its on average smaller/narrower pale rump patch than the nominate; tail fork on average considerably (c. 20%) shallower; rump patch far less contrasting by virtue of the often many fewer pure or almost pure white feathers therein, in addition to its being narrower; the wings, especially the flight feathers, appear substantially less glossed; head-sides and ear-coverts typically appear much less solidly dark, thus its cap seems smaller, with much more of a paler and contrasting neck-collar; and appears considerably more patterned below, displaying much more obvious shaft-streaks on the lower breast and belly, and a sharper division between the darker throat and breast, versus paler (and grayer) remainder of the underparts (3 Kirwan, G.M., H. Shirihai, and M. Schweizer (2018) A morphological revision of Mascarene Swiftlet Aerodramus francicus, with the description of a new subspecies from Reunion. Bulletin of the British Ornithologists’ Club 138(2):117–130. Close ).

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Thought to be closest to Seychelles Swiftlet (A. elaphrus), and sometimes considered conspecific (10 Peters, J. L. (1940). Check-list of Birds of the World. Volume 4. Harvard University Press, Cambridge, MA, USA. Close , 11 Gaymer, R., Blackman, R.A.A., Dawson, P.G., Penny, M. and Penny, C.M. (1969). The endemic birds of Seychelles. Ibis 111(2):157–176. Close ); has alternatively been lumped with White-nest Swiftlet (A. fuciphagus), although the two do not appear to be closely related.

Subspecies A. f. saffordi is named for Roger Safford, conservationist and ornithologist, and one of the co-editors of a regional handbook to the birds of the southwest Indian Ocean (2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ).

No information.

Mauritius and Reunion (Mascarene Islands).

Occurs over wide range of habitats throughout both islands, foraging from sea level to 3,069 m, the highest point on Reunion (12 Barré, N., Barau, A. and Jouanin, C. (1996). Oiseaux de la Réunion. Second edn. Les Éditions du Pacifique, Paris. Close , 2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ). Nesting caves are typically sited in lava tunnels or tubes, apparently most frequently in younger lava (13 Staub, J.J.F. (1973). Oiseaux de l’Île Maurice et de Rodrigues. Mauritius Printing Co., Port Louis, Mauritius. Close , 4 Cheke, A. S. (1987). The ecology of the smaller landbirds of Mauritius. In Studies of Mascarene Landbirds (Diamond, A. W., Editor), Cambridge University Press, Cambridge, UK. pp. 151–207. Close , 14 Safford, R.J. (2001). The Comoros. Pp. 185–190 in: Fishpool, L.D.C. & Evans, M.I. (eds), Important Bird Areas in Africa and associated islands: Priority sites for conservation. Pisces Publications and BirdLife International (BirdLife Conservation Series No.11), Newbury and Cambridge, UK. Close , 2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ).

Resident. Records from Madagascar no longer considered acceptable (2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ).

Gregarious, foraging in flocks (rarely large). Usually feeds at least 20 m above ground, though will feed lower over lakes and during cloudy periods (4 Cheke, A. S. (1987). The ecology of the smaller landbirds of Mauritius. In Studies of Mascarene Landbirds (Diamond, A. W., Editor), Cambridge University Press, Cambridge, UK. pp. 151–207. Close ). In two boluses of prey collected by adults to feed nestlings, Diptera (of 13 families) predominated (50–60%, especially chironomid and drosopholid flies), with addition of Hemiptera, beetles, small moths (microlepidoptera), barkflies (Psocoptera) and small quantities of spiders; most prey 1.6–3.2 mm long, though some flying ants 5.2–8.2 mm with an anthomyid fly measuring 4.2 mm (2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ). Foraging ends never more than 35 minutes after dark and more typically within 30 minutes of dusk (4 Cheke, A. S. (1987). The ecology of the smaller landbirds of Mauritius. In Studies of Mascarene Landbirds (Diamond, A. W., Editor), Cambridge University Press, Cambridge, UK. pp. 151–207. Close ).

Two sounds recorded: twitter calls and echolocating clicks (15 Horne, J.F.M. (1987). Vocalisations of the endemic land-birds of the Mascarene Islands. Pp. 101–150 in: Diamond, A.W. ed. (1987). Studies of Mascarene Landbirds. Cambridge University Press, Cambridge. Close ). Calls include a repeated throaty, hoarse or hissing cheeee or churrr, each note lasting 0.5 seconds and repeated every 0.5–1.0 seconds, often uttered by several or even many birds simultaneously and given in conjunction with clicks. Uses echolocation inside nesting caves, more occasionally heard in open (perhaps mostly in misty conditions) (2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ); double-clicking sounds typical of many Asian species of Aerodramus (16 Price, J. J., K. P. Johnson, and D. H. Clayton (2004). The evolution of echolocation in swiftlets. Journal of Avian Biology 35(2):135–143. Close ), emitting repeated high-bandwidth clicks at a rate of c. 5–10 clicks per second and mainly at 4–8 kHz (especially 5 kHz) but some harmonics reaching < 16 kHz, sounding like a rattling tic-tic-tic-tic-tic..., and their tempo increasing when entering nesting cave or when in proximity to other birds (2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ).

Occasionally observed mobbing Mauritius Kestrels (Falco punctatus), but no observed cases of predation (4 Cheke, A. S. (1987). The ecology of the smaller landbirds of Mauritius. In Studies of Mascarene Landbirds (Diamond, A. W., Editor), Cambridge University Press, Cambridge, UK. pp. 151–207. Close ); Mascarene Swiftlet is, however, sometimes hunted by Sooty Falcons (Falco concolor) (2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ).

Virtually all data from Mauritius (4 Cheke, A. S. (1987). The ecology of the smaller landbirds of Mauritius. In Studies of Mascarene Landbirds (Diamond, A. W., Editor), Cambridge University Press, Cambridge, UK. pp. 151–207. Close , 2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ). Season not clearly defined, with eggs and young present in every month except April and May 1974 during a 16-month study of two colonies from October 1973 to January 1975, and even during these months nests were being built; these two sites, although geographically close, were not in synchrony. Openings of subterranean waterways typically used for breeding, often sited in canefields, and colonies usually compact. Self-supporting, bracket-shaped nest of Usnea lichen filaments, sometimes moss (five genera identified in nests on Reunion), liverworts, Casuarina needles (especially in coastal areas) or conifer needles, but each nest often constructed of a single material, agglutinated with saliva which is copious only in hinge; size 30–60 mm × 55–85 mm and 15–20 mm deep. Adjacent nests often attached. Two eggs typical, one rarely, chalky white, size 18.3–21.7 × 12.5–13.4 mm (5 Cheke, A.S. and Jones, C.G. (1987). Measurements and weights of the surviving endemic birds of the Mascarenes and their eggs. Pp. 403–422 in: Diamond (1987). Close ); four weeks from starting fresh nest to laying, or 4–6 weeks if nest destroyed, though slower if starting again after a non-breeding period; mean relaying interval 27 days; interval between clutches c. 3 weeks, allowing for two broods in 6.5 months or three in 9.5 months. Incubation period probably 21–23 days; young hatch synchronously but probably fledge asynchronously, and are probably fed by both adults, mean fledging period probably 45–55 days. Hatching success high, 84% in non-vandalized nests, but 24 of 44 nests destroyed by vandals, and 94% of hatchlings fledged; overall success 81%, with failure attributed to eggs being ejected by adults, young being predated by cockroaches (Blattodea), post-cyclone flooding and direct persecution by humans, perhaps also by other predators, e.g. feral cats. Young usually switch colonies, nesting away from their natal site.

No information.

Not globally threatened. Currently considered Near Threatened. Restricted-range species: present in Reunion EBA and Mauritius EBA (17 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 ). Population limited by paucity of suitable nest-sites; most recently estimated at 6,000–15,000 mature individuals. Generally rather common to locally abundant on Reunion and Mauritius; on latter island declined during 20th century until 1970s (4 Cheke, A. S. (1987). The ecology of the smaller landbirds of Mauritius. In Studies of Mascarene Landbirds (Diamond, A. W., Editor), Cambridge University Press, Cambridge, UK. pp. 151–207. Close ), but was increasing again by late 1990s, when 34 caves were found to support colonies, but very few held more than 100 individuals and total population was estimated at no more than c. 2,600 individuals (14 Safford, R.J. (2001). The Comoros. Pp. 185–190 in: Fishpool, L.D.C. & Evans, M.I. (eds), Important Bird Areas in Africa and associated islands: Priority sites for conservation. Pisces Publications and BirdLife International (BirdLife Conservation Series No.11), Newbury and Cambridge, UK. Close , 2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ). On Reunion, where numbers historically always considered smaller than on Mauritius, by mid 1990s population was estimated at c. 10,000 birds (some sites holding more than 1,500 and one, at La Chapelle, said to hold > 10,000 nests) (18 Cheke, A. S., and J. P. Hume (2008). Lost Land of the Dodo: An Ecological History of Mauritius, Réunion and Rodrigues. T. & A. D. Poyser, London, UK. Close ). Nevertheless, several colonies threatened by actions of speleologists and direct persecution (2 Safford, R., and F. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ), while many cave sites inaccessible which, though granting protection, limits estimation of population size.