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Mariana Swiftlet Aerodramus bartschi
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This species qualifies as Endangered because it has undergone a rapid population decline, presumably owing to pesticide-use and predation by the introduced brown tree snake Boiga irregularis on Guam. Furthermore, a very rapid decline is expected following establishment of the brown tree snake on Saipan, its stronghold.

Taxonomic source(s)
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Taxonomic note
Aerodramus bartschi (del Hoyo and Collar 2014) was previously placed in the genus CollocaliaCollocalia inquieta (Sibley and Monroe 1990, 1993) was previously split into C. bartschi following Browning (1993) and AOU (1998) and C. inquieta following Browning (1993).

Aerodramus bartschi AOU checklist (1998 + supplements), Collocalia bartschi Mearns, 1909

11 cm. Swiftlet with dark greyish-brown upperparts and head. Silvery grey-white throat and upper breast. Remainder of underparts darker and greyer. Shallow fork-tail. Plumage lacks any noticeable sheen. Voice Chirps and twitterings. Makes echolocation clicks inside caves.

Distribution and population
Collocalia bartschi is endemic to Guam (to USA) and the Northern Mariana Islands (to USA), and was introduced to Oahu, Hawaiian Islands (USA) in the early 1960s. On Guam, it was very abundant but, from the mid-1960s to the early 1970s, it underwent a precipitous decline (Jenkins 1983). In 1999, only three colonies remained, the largest holding c.700 birds (total population c.800) (G. Wiles unpublished data). A 2008 report by the U.S. Navy estimated that the population on Guam has increased to around 1,150 individuals (Grimm 2008). In the Northern Marianas, populations disappeared from Rota and Tinian in the 1970s, although, on Tinian, it was possibly only nomadic (Engbring et al. 1982). In 1982, estimates were 9,120 on Saipan and 1,022 on uninhabited Aguijan (Engbring et al. 1982) but, more recently, estimates are c.5,000 (five colonies) and 416 (seven colonies), respectively (J. Cruz in litt. 2007, G. Wiles unpubl. data). On Oahu, it survives in a single known breeding colony in a small tunnel in the Ko`olau Mountains, although similar irrigation tunnels are common and thus other small colonies may exist (Chantler and Driessens 1995). Observations there in 1997 suggested a minimum of 17 breeding pairs (66 birds in total [Wiles and Woodside 1999]), whilst monitoring during 2009-2010 recorded up to 50 nesting pairs (E. Vanderwerf in litt. 2012). The number of nesting pairs and fledglings on Oahu was lower in 2011 because rats invaded the nesting tunnel after rat control was interrupted (E. Vanderwerf in litt. 2012).

Population justification
The population estimate of 3,200-3,500 individuals is derived from G. Wiles in litt. and Wiles & Woodside (1999). This is roughly equivalent to 2,100-2,300 mature individuals.

Trend justification
Population estimates have fluctuated over the last two decades but appear to be increasing. Recent population estimates on Saipan indicate that the population has increased to approximately 5,400 individuals from 1985 to 2005 (J. Cruz et al. in litt. 2007). The population on Guam is also believed to have increased to approximately 900 individuals from 1983 to 2006 (A. Brooke in litt. 2006) while the population on Aguijan appears stable at around 400 individuals based on 2002 surveys (J. Cruz et al. in litt. 2007). However, on Saipan, the species's stronghold, brown tree snake Boiga irregularis is in the process of becoming established (Rodd and Savidge 2007), which  is expected to cause a very rapid decline.

It feeds over coastal and interior forest and grassland (and formerly mangroves), capturing small insects in flight, preferring forest on Guam and Aguijan (G. Wiles unpublished data). It breeds and roosts in colonies in caves that typically hold a few to 700 birds (G. Wiles unpublished data). Nesting occurs year-round, but is greatest from late January to September or October. One egg is laid per clutch and pairs probably lay more than one clutch per year (G. Wiles unpublished data).

The cause of the decline on Guam and the extinction on Rota may relate to loss of insect prey through pesticide-use (Kohley et al. 2006). Currently, predation by brown tree snake Boiga irregularis is the primary limiting factor on Guam and interactions with introduced mud dauber wasps Vespula sp. may interfere with recovery (the additional weight of wasps nests causes swiftlet nests to fall from cave walls). On Saipan, exotic cockroaches (which damage and destroy nests by consuming nest material and swiftlet saliva gluing them to cave walls), predation by brown tree snake (which is in the process of becoming established on the island [Rodd and Savidge 2007]) and possible disturbance by humans and feral mammals are the main threats (Wiles and Woodside 1999, A. Saunders in litt, G. Wiles unpubl. data).

Conservation Actions Underway
On Guam, snakes have been trapped at the main colony. Colonies have been censused regularly, nesting has been observed and foraging ranges mapped. On Rota, surveys have been conducted confirming that there is now sufficient insect prey to allow successful reintroduction. On Saipan and Aguijan, colonies have been censused periodically and insecticide applied to kill cockroaches (G. Wiles in litt. 2000). Rat control on Oahu has resumed but is being done less often than previously because access to the site has become more difficult (E. Vanderwerf in litt. 2012).
Conservation Actions Proposed
Continue monitoring all populations. On Saipan, eradicate the brown tree snake and limit cave disturbance. On Guam, facilitate recolonisation of caves historically used by large colonies. On Rota, reintroduce birds (G. Wiles in litt. 2000). On Guam and Saipan, eradicate or control dauber wasps and cave dwelling cockroaches, respectively. On Oahu, control introduced black rats Rattus rattus near nesting tunnel entrance.

Browning, M. R. 1993. Species limits of the cave swiftlets (Collocalia) in Micronesia. Avocetta 17: 101-106.

Chantler, P.; Driessens, G. 1995. Swifts: a guide to the swifts and treeswifts of the world. Pica Press, Robertsbridge, U.K.

Engbring, J.; Ramsey, F. L.; Wildman, V. J. 1982. Micronesian forest bird survey, 1982: Saipan, Tinian, Agiguan, and Rota. U.S. Fish and Wildlife Service, Honolulu.

Grimm, G. 2008. Mariana swiftlet surveys on Naval Munitions Site, Guam. U.S. Navy, NAVFAC Marianas, Guam.

Jenkins, J. M. 1983. The native forest birds of Guam. American Ornithologists' Union, Washington, D.C.

Kohley, C. R.; Kershner, E. L.; Kremer, S. 2006. The assessment of the diet of the endangered Mariana Swiftlet. Wings without borders: IV North American Ornithological Conference, October 3-7 2006, Veracruz, Mexico, pp. 177. American Ornithologists' Union, Waco, TX, U.S.A.

Lee, L. M.; Clayton, D. H.; Griffiths, R.; Page, R. D. M. 1996. Does behavior 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.

Morton, J. M.; Amidon, F. A. 1996. Development of field techniques for studying and restoring the Vanikoro Swiftlet (Aerodramus vanikorensis bartschi) on Guam.

Wiles, G. J.; Woodside, D. H. 1999. History and population status of guan swiftlets on O'ahu, Hawai'i. 'Elepaio 59: 57-61.

Further web sources of information
Explore HBW Alive for further information on this species

View photos and videos and hear sounds of this species from the Internet Bird Collection

Text account compilers
Derhé, M., Mahood, S., O'Brien, A., Stattersfield, A.

Cruz, J., Saunders, A., Wiles, G.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2014) Species factsheet: Aerodramus bartschi. Downloaded from on 01/08/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from on 01/08/2014.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Key facts
Current IUCN Red List category Endangered
Family Apodidae (Swifts)
Species name author Mearns, 1909
Population size 2100-2300 mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 730 km2
Country endemic? No
Links to further information
- Additional Information on this species