Mariana Swiftlet Aerodramus bartschi Scientific name definitions

11 cm; 6·5–8 g (1 Dunning, J. B., Jr. (2008). CRC Handbook of Avian Body Masses. Second edition. CRC Press, Boca Raton, FL, USA. Close ). A small swiftlet with a moderately forked tail; warm brown upperparts lacking sheen and with uniform rump; underparts darker grey beneath silver-grey throat; tarsi bare or lightly feathered; supraloral patch missing or much reduced; underparts lack shaft streaks. Notably paler than A. inquietus. Available information suggests the species is probably capable of echolocation.

Introduced to Oahu, Hawaii.

Northern Mariana Is (Saipan and Aguijan; extirpated from Rota and Tinian) and Guam.

Occurs over a wide range of cleared and forested habitats in interior and on coast, including mangroves.

Nomadic movements account for occasional temporary gatherings at dusk or for longer periods, and absence from certain islands.

Tends to be most noticeably gregarious in evenings when large groups feed very low, not moving up and away until nightfall. Feeding times and habits similar to those of sympatrically occurring sheath-tailed bats (Emballo­nura).

Described as weak chirps and twitterings (2 Chantler, P.J. and Driessens, G. (1995). Swifts. A Guide to the Swifts and Treeswifts of the World. Pica Press, Robertsbridge, UK. Close ).

Active colonies Mar–May, but on Oahu (Hawaii), where introduced, nesting has been recorded year-round, albeit with a peak in May–Sept (3 Johnson, N.C., Haig, S.M., Mosher, S.M. and Hollenbeck, J.P. (2017). Reproductive success of Mariana Swiftlets (Aerodramus bartschi) on the Hawaiian island of O’ahu. J. Field Orn.. 88(4): 362–373. Close ). Colonial, up to 250 nests with clusters of 25–50. Nest cylindrical, constructed of plant material, birds adding to it each season, supported by niche in cave wall, or in human-made tunnel in Halava Valley, on Oahu, Hawaii (3 Johnson, N.C., Haig, S.M., Mosher, S.M. and Hollenbeck, J.P. (2017). Reproductive success of Mariana Swiftlets (Aerodramus bartschi) on the Hawaiian island of O’ahu. J. Field Orn.. 88(4): 362–373. Close ); on Guam principally composed of Neckeropsis lepiniana moss, and agglutinated by large amounts of hardened saliva; size typically 50–60 mm wide, 65–70 mm in length with a shallow cup c. 10 mm deep. Clutch single white egg, size 17–19·7 mm × 10·3–13 mm, mass 0·8–1·6 g (4 Reichel, J. D., Collins, C. T., Stinson, D. W. and Camacho, V. A. (2007). Growth and development of the Mariana Swiftlet. Wilson Journal of Ornithology. 119(4): 686–692. Close ), incubated 17–30 days (mean c. 24 days on Oahu or 22·9 days on Saipan), with a nestling period of 41–84 days (mean 55 days) on Oahu, or 40–55 days (mean c. 47 days) on Saipan (4 Reichel, J. D., Collins, C. T., Stinson, D. W. and Camacho, V. A. (2007). Growth and development of the Mariana Swiftlet. Wilson Journal of Ornithology. 119(4): 686–692. Close , 3 Johnson, N.C., Haig, S.M., Mosher, S.M. and Hollenbeck, J.P. (2017). Reproductive success of Mariana Swiftlets (Aerodramus bartschi) on the Hawaiian island of O’ahu. J. Field Orn.. 88(4): 362–373. Close ); young hatch naked, and weigh 1–1·2 g, but are 5·4–10·4 g (mean c. 8 g) around fledging (4 Reichel, J. D., Collins, C. T., Stinson, D. W. and Camacho, V. A. (2007). Growth and development of the Mariana Swiftlet. Wilson Journal of Ornithology. 119(4): 686–692. Close ). On Oahu, estimated nest success was 63% over five seasons, with more than half (52%) of nest failures being attributed to eggs found on the tunnel floor (3 Johnson, N.C., Haig, S.M., Mosher, S.M. and Hollenbeck, J.P. (2017). Reproductive success of Mariana Swiftlets (Aerodramus bartschi) on the Hawaiian island of O’ahu. J. Field Orn.. 88(4): 362–373. Close ).

ENDANGERED. Previously considered not globally threatened. Restricted-range species: present in Mariana Islands EBA. Marked decline seems apparent since species was recorded as abundant on both Guam and Saipan in 1949. By 1987, it had become extinct on Rota, was approaching extinction on Guam and was uncommon on Saipan, Tinian and Agiguan, with field work on the last-named island recording the species in very small numbers in 2008, compared to those observed in 1982, but this followed two years (2000 and 2002) when the species was not recorded at all there (5 Amidon, F., Camp, R.J., Marshall, A., Pratt, T.K., Williams, L., Radley, P. and Cruz, J.B. (2014). Status and trends of the land bird avifauna of Aguiguan, Mariana Islands. Bird Conserv. Int. 24(4): 505–517. Close ); further surveys needed. Population on Saipan recently estimated at c. 5000 individuals (4 Reichel, J. D., Collins, C. T., Stinson, D. W. and Camacho, V. A. (2007). Growth and development of the Mariana Swiftlet. Wilson Journal of Ornithology. 119(4): 686–692. Close ). Introduced to Oahu, Hawaii, in 1962, and now breeds in Halawa and Moanalua Valleys, although population appears to be very small. Just 12 pairs found breeding in 1989, but more recently the population appears to have grown somewhat, although rat (Rattus spp.) predation of both nests and adults is still very much a limiting factor (3 Johnson, N.C., Haig, S.M., Mosher, S.M. and Hollenbeck, J.P. (2017). Reproductive success of Mariana Swiftlets (Aerodramus bartschi) on the Hawaiian island of O’ahu. J. Field Orn.. 88(4): 362–373. Close ).