ARTICLES ON HAWAIIAN BIRDS AND BIRDWATCHING

The Mariana Swiftlet (Aerodramus bartschi)

This species of Swiftlet is native to forested islands in Micronesia including the Mariana Islands and Guam in the southwest Pacific Ocean but has been introduced in small numbers to the Upper Halawa Valley and Moanalua Valley on O'ahu in the Hawaiian Islands, although it seems likely that the species is currently restricted to the former site, at least as a breeding bird. The species is listed as Endangered in the Mariana Islands under the Endangered Species Act of Guam, September 1981; Guam Public Law 15-36, June 18, 1979, although the species is not listed by CITES nor by the IUCN (Red Data Book 1981). The very similar Aerodramus vanikorensis or Uniform Swiftlet is found from the East Indies and Philippines to Melanesia and has at times in the past been considered conspecific, although current authorities consider both to be valid species.

The species is also sometimes referred to by other names, most of which are either incorrect or are also applied to other similar species, names include Mariana Gray Swiftlet, Gray Swiftlet, Caroline Swiftlet, Caroline's Swiftlet, Lowland Swiftlet, Mauritius Swiftlet, Edible-nest Swiftlet, Guam Edible-nest Swiftlet, Uniform Swiftlet, Cave Swiftlet, Guam Cave Swiftlet, Mossy-nest Swiftlet, Island Swiftlet, Swiftlet, Vanikoro and Yayaguak. Mariana Swiftlet picture taken from the USGS website [www.mesc.usgs.gov/resources/education/ bts/impacts/birds.asp](2001).

This species of Swiftlet is characterised by having sooty black upper parts with a slightly paler rump. The underparts are dark gray but with a brownish tinge. Some white is present at the base of the feathers in the loreal region. The tarsi are naked and the irises are dark hazel. The plumage of both sexes is alike. Weights of 21 birds averaged 7.4 grams (range = 6.4 to 9.0 grams). Other measurements include: wing, average of 107.6 mm and 108 mm; tail, average of 52.3 mm; exposed culmen, average of 4.0 mm; tarsus, average of 10.4 mm, and wingspan, maximum of 233 mm.

Listed below are taxonomic names and synonyms that have been used to describe A. v. bartschi.

Hirundo vanikorensis	Quoy & Gaimard 1830
Collocalia inquietus	Kittlitz 1836
Collocalia fuciphaga	Sclater 1865
Collocalia nidifica	Gray 1869
Collocalia vanicorensis	Finsch 1876
Collocalia fuchphaga	Wheeler 1900
Collocalia fuciphaga fuciphaga	Oberholser 1906
Collocalia unicolor amelis	Oberholser 1906
Collocalia bartschi	Mearns 1909
Collocalia fuciphaga tachyptera	Oberholser 1912
Collocalia fuciphaga bartschi	Kuroda 1922
Collocalia vanikorensis bartschi	Mathews 1927
Collocalia vanikorensis bartschi	Mayr 1936
Collocalia germani bartschi	Mayr 1937
Collocalia inexpectata bartschi	Peters 1940
Collocalia inexpectata	Strophlet 1946
Collocalia vanikorensis	Owen 1977
Aerodramus vanikorensis bartschi	Pratt, Bruner and Berrett 1979
Collocalia francica bartschi	Howard and Moore 1980
Aerodramus inquieta bartschi	Edwards 1982
Aerodramus bartschi	Pratt 1986, del Hoyo 1999

Information in table taken from the CMI website (1996).

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Baker lists the following specimens: 21 specimens from Guam and one from Rota in the National Museum of Natural History; and 18 specimens from Guam and 8 from Saipan in the American Museum of Natural History. Also, 2 specimens are in the collection of the Bishop Museum, Honolulu. An unknown number of specimens may exist in other collections. The type specimen of A. v. bartschi is from Guam and is located in the National Museum of Natural History. Photographs of Vanikoro Swiftlets are held by the Guam Division of Aquatic and Wildlife Resources, Department of Agriculture, Agana,
Guam. The taxonomy of this group of swiftlets is in much debate. Virtually all current authorities recognize bartschi as either a
subspecies (usually of vanikorensis) or as its own monotypic species. The generic name continues to be debated as well.
Several common names have been applied to this species. These include Edible-nest Swiftlet, Guam edible-nest Swiftlet, Gray Swiftlet, Uniform Swiftlet, Mauritus Swiftlet, Caroline Swiftlet, Carolines Swiftlet, Guam Cave Swiftlet, Mossy-nest Swiftlet, Island Swiftlet, and the Lowland Swiftlet. The species was previously listed pursuant to the Endangered Species Act of 1973, as amended under the common nameVanikoro Swiftlet. "Yayaguak" is the local name for swiftlets used by Chamorro residents in the Mariana Islands. Most recent literature names the species as Gray Swiftlet, Island Swiftlet or Guam Swiftlet. The name was changed by the AOU to Mariana Swiftlet as the species is not confined to Guam in the Mariana Islands.

According to del Hoyo (1999) the genus is often merged into Collocalia (cf. Mearns 1909 in above table) and forms a superspecies with A. salangana (Mosy-nest Swiftlet), A. vanikorensis (Uniform Swiftlet), A. pelewensis (Palau Swiftlet) and A. inquietus (Caroline Swiftlet), all of which were formally considered conspecific. The genus was also previously lumped with A. pelewensis and sometimes associated with A. fuciphagus germani and A f. inexpectatus (Edible-nest Swiftlet). Sometimes it is considered a race of A.inquietus (Caroline Swiftlet) by some authors.

MARIANA SWIFTLETS IN HAWAI'I

Mariana Swiftlets were introduced to the Halawa and Moanalua Valleys on O'ahu in 1962, where a small population was established with birds nesting in a 30 to 40 meter long man-made irrigation tunnel. Apparently they are the only Mariana Swiftlets in the Pacific (and perhaps elsewhere) that have been reported to nest in non-natural caves, although according to Pratt they inhabit natural and man-made caves, such as abandoned World War II gun implacements on Micronesia. Mariana Gray Swiftlets roost exclusively in caves.

Today, due to construction of the H-3 Freeway through the Halawa Valley in the 1990's the nesting cave and prime feeding habitat area is out of bounds to all but a few researchers or those with special access permission and so the species can be very difficulat to observe. Although the species occasionally wanders from these valleys (at least as far as Pearl City) they are usually rather sedentary and often fly at height, which makes observations of the species away from the northern end of Halawa Valley unusual. Although the actual nesting site is off-limits, birds are seen from the new freeway and from nearby peaks, although even here they very rarely wander far away and are often difficult to locate as they are either high up or very distant. Anybody wishing to see this species should try to get on the ridges overlooking the valley as this is the best chance at present for observing this species. The end of the Aiea Ridge Trail is a good place to look as birds have been seen several times over and below the trail.

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GENERAL LIFE HISTORY

(Much of the following text comes from the Conservation Management Institute website (1996) draft taxonomy text on the Mariana Gray Swiftlet and uses the name of Aerodramus bartschi and details information for the Mariana and Hawai'i birds).

The Mariana Gray Swiftlet (Aerodramus bartschi) has been designated an Endangered species pursuant to the Endangered Species Act of 1973 (50 CFR 17.11; P.L. 93-205, 87 Stat. 884; 16 U.S.C. 1531-1540), as amended. The subspecies has this status in the Territory of Guam and the Commonwealth of the Northern Mariana Islands. This subspecies is protected by the Lacey Act (P.L. 97-79, as amended; 16 U.S.C. 3371 et seq.) which makes it unlawful to import, export, transport, sell, receive, acquire, or purchase any wild animal (alive or dead including parts, products, eggs, or offspring):
(1) in interstate or foreign commerce if taken, possessed, transported or sold in violation of any State law or regulation, or foreign law; or (2) if taken or possessed in violation of any U.S. law, treaty, or regulation or in violation of Indian tribal law.
It is also unlawful to possess any wild animal (alive or dead including parts, products, eggs, and offspring) within the U.S.
territorial or special maritime jurisdiction (as defined in 18 U.S.C. 7) that is taken, possessed, transported, or sold in
violation of any State law or regulation, foreign law, or Indian tribal law.

HABITAT ASSOCIATIONS and FOOD HABITS

Mariana Gray Swiftlets have been reported to forage over a wide variety of habitats including grasslands, limestone forest,
ravine forest, and coconut groves as well as Orchards, Groves, Vineyards, Nurseries, Mixed Rangeland, Evergreen Forest Land, Forested Wetland and Nonforested Wetland,where they are carnovores of General Arthropods. A. v. bartschi feeds on insects captured in flight, although detailed food studies have not been conducted and insects species that are eaten are not known. These habitats on Guam have been described in detail by Fosberg and Stone. On Saipan, they also feed over tangan-tangan (Leucaena leucocephala) forests. Clifflines, grassy hills, and grassy ravines are among the preferred foraging habitats. On Guam, the colony inhabiting the eastern side of the Naval Magazine feeds over savanna grasslands dominated by Miscanthus and ravine forest. Birds from this colony also feed over several types of seasonally-flooded wetlands. These areas are designated in the National Wetlands Inventory as palustrine, forested, broad-leaved evergreen and palustrine, emergent, persistent. No specific information exists on the habitat use of Mariana gray swiftlets on Saipan and Aguijan. On Oahu, swiftlets occur over forested hills and valleys.
Mariana Gray Swiftlets roost exclusively in caves. All caves reported to be used by swiftlets are natural except for one in Hawai'i which was a 30 to 40 meter long man-made irrigation tunnel. According to Pratt (1986) they inhabit natural and man-made caves, such as abandoned World War II gun implacements on Micronesia. Caves used by A. (v.) bartschi for roosting and nesting are formed from limestone rock and occur in limestone forest and ravine forest. Colonies of swiftlets are also known to roost in at least three limestone sinkholes. Caves may be as short as 10 meters in length, but are normally much longer. Cave chambers used for nesting are four meters or more in height. Colonies of swiftlets are also known to roost in at least three limestone sinkholes. One of these on Guam was 18 meters wide and 23 meters deep. Two others on Saipan and Guam were 7 to 10 meters deep and 41 meters deep, respectively. There does not appear to be any seasonal changes in habitat use by Mariana Gray Swiftlets.

HOME RANGE/TERRITORY:

Little is known about the movements or home ranges of A. v. bartschi. On Guam, birds thought to be from the colony at the
Naval Magazine are seen feeding most often within 1.5 kilometers of their roosting cave. A few sightings occur up to five
kilometers away. Swiftlets forage singularly, in pairs, or in flocks of up to several hundred birds. It seems unlikely that individuals have or defend preferred feeding territories, since they are dependent at times upon shifting winds to concentrate the prey at different times and places. Mariana Gray Swiftlets are highly colonial roosters and nesters. They typically form colonies numbering from a few individuals toseveral thousand birds. A colony on Guam contains 250-300 birds while on Saipan there are at least 200 birds. Mariana gray swiftlets roost in caves at night. Some birds may return to caves during the day to rest or for nesting. Swiftlets are diurnal and crepuscular feeders. Marshall noted on Saipan that large flocks of A. v. bartschi fed for only a few weeks in any one part of the island. He believed their movements may have been seasonal. Nests are composed of moss held tightly together and sealed to the cave surface by copious amounts of hardened mucus-like saliva. On Guam, nests are made of Neckeropsis lepiniana, a moss that is common in forests near nesting caves. In Hawai'i a liverwart (Herberta spp.) is used as the preferred nesting material (superficially, it strongly resembles Neckeropsis).

REPRODUCTIVE CHARACTERISTICS:

Clutches of A. (v.) bartschi contain single eggs laid between January and July. Nesting possibly occurs during theremainder of the year but has not been reported previously. Nesting is not synchronous within colonies. Double clutches or renesting attempts have not been observed. The incubation period of Mariana grey swiftlets is at least 12 days. Other breeding information is not available for these swiftlets. Young Mariana Gray Swiftlets are highly altricial. They require two to three weeks to open their eyes and develop rudimentry feather tracts. One nestling took 35 days to fledge. It is not known whether both adults participate in incubation, brooding, or feeding of the young.

MIGRATION PATTERNS:

Swiftlets are not known to be migratory, although Marshall describes their former presence on Tinian as being nomadic.

Distribution of Aerodramus vanikorensis	Distribution of Aerodramus bartschi

Maps taken from the Handbook of the Birds of the World, Volume 5, edited by del Hoyo et al. (1996).

POPULATION BIOLOGY:

The population biology of the Mariana gray swiftlet is not known. Current limiting factors of populations are not understood but are probably closely related to the reasons for the specues decline.

MANAGEMENT PRACTICES

MANAGEMENT PRACTICE	RESULT
Restricting/regulating human disturbance of populations	Beneficial
Land Acquisition	Beneficial
Controlling/Restricting Pesticide Use	Beneficial
Transplanting wild animals	Beneficial
Disease Control Measures	Beneficial
Controlling/Removing Exotic Vertebrates	Beneficial
Artillery/Explosions	Adverse
Artillery/Explosions	Existing
Harassment/Vandalism/Indiscriminate Killing	Adverse
Harassment/Vandalism/Indiscriminate Killing	Existing
Disease	Adverse
Disease	Existing
Predation	Adverse
Predation	Existing
Applying pesticides	Adverse
Applying pesticides	Existing
Exotic/Feral/Introduced Species	Adverse
Exotic/Feral/Introduced Species	Existing

Information in table taken from the CMI website (1996).

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MANAGEMENT PRACTICES:

Many authors have referred to the past abundance of A. (v.) bartschi on Guam and Rota. Reasons for the decline of Mariana gray swiftlets are unknown but hypothesized causes include pesticide poisoning, introduced predators, disease, typhoons, and disturbance or permanent loss of nesting caves. To date, no infectious diseases have been isolated on Guam that could account for the decline. Feral dogs, cats and rats probably have little or no effect on swiftlets, which are aerial feeders and cave nesters. However, the Brown tree snake (Boiga irregularis), an introduced snake present only on Guam, is a more likely predator. Data indicates that it is responsible for the sharp decline in some of Guam's other native birds. Pesticides residues are apparently not a current problem for swiftlets or their prey on Guam but pesticides may have had some impact in the past.
Typhoons are a regular occurrence under which all species of native wildlife in the Marianas have evolved. Typhoons might cause temporary declines in the swiftlets populations but presumably would not incur permanent losses. Caves were used for a variety of defensive purposes by the Japenese military in World War II. During the invasion of Saipan, Tinian and Guam, a number of caves were destroyed or highly disturbed. These activities probably affected swiftlets for at least a short period of time before reuse. Guano has been mined from swiftlet caves on Rota, Aguijan, Tinian and Saipan and this activity may have disturbed birds that were roosting or nesting.

The Marianas race of Vanikoro Swiftlet has declined for unknown reasons. The Vanikoro Swiftlet Recovery Plan now in
preparation emphasizes three recovery goals: (1) complete protection of nesting and roosting caves, (2) development of a complete understanding of limiting factors, and (3) reestablishment of swiftlets to suitable habitat (i.e. historically used caves) within the historical range of the species. Securing caves and a buffer zone around each cave would involve transferring ownership or managing authority to a conservation agency. Caves could then be mangaged to reduce disturbance by people, and to do so may require constructing barriers at cave entrances. It may also be necessary to "snake-proof" caves by various means yet to be determined. Research on swiftlets should receive high priority and would include general autecological
studies, determination of the causes of decline (potentially, the Brown tree snake, pesticides, human disturbance, and diseases),
surveys for additional nesting caves,and continued censusing of known swiftlet caves. Once cave management and research are well underway, it may become feasible to reestablish swiftlets in abandoned caves, though the techniques for doing this are yet unknown. Recovery actions underway include: (1) surveys for nesting caves and censusing of these caves and (2) transfer of lands encompassing caves from the Marianas Public Land Corporation to the Division of Fish and Wildlife, Commonwealth of the Northern Marianas Islands.

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