The Koloa Maoli or Hawaiian Duck (Anas wyvilliana) - Distribution and Population Status.

The Hawaiian Duck is small and brownish with orange legs but has a highly variable plumage with some birds having various amounts of red-brown, chestnut, mottling, streaks and in the males often a green sheen to the head and neck. The bill varies from grey through to almost orange. In flight the species shows a green or sometimes purplish speculum bordered on each side by white and has a white underwing. Males are usually slightly larger than the females.

In the past the Hawaiian Duck has often been treated as a race or sub-species of the Mallard, and it is obvious from its behaviour and morphology that the species is closely related to the North American Mallard complex (Phillips 1912). It has been shown that the Hawaiian Duck is genetically distinct from the Mallard based on allozymic evidence (Griffin & Browne 1990). It was also shown that the species is closely allied to the Mottled Duck (A. fulvigula) and Black Duck (A. rubripes) (USFWS 1999), and distinct from the Mallard at the mitochondrial level.

Historical Range and Population Status

The Hawaiians referred to the Koloa as Koloa Maoli to differentiate the species from migrant ducks which visit the islands, mainly during winter. Captain Cook was probably referring to this species when he landed on Kaua'i in 1778 and wrote in his journal of a wild duck being present. It was not until the voyage of the H.M.S. Challenger in 1875 that the bird was described to science by P.L.Sclater as the "Hawaiian Duck" - Anas wyvilliana (Bryan 1939).

The Koloa Maoli (referred to from now on as Koloa) was formerly present on all but two of the main islands, being absent from Lana'i and Kaho'olawe (Munro 1944). The species began to decline around the turn of the 20th Century (Henshaw 1902), this being attributed to habitat loss, hunting, predation by Mongoose (Herpestes auropunctatus), Dogs (Canis familiaris), Cats (Felis catus), Rats (Rattus sp.) and genetic diluting by cross-breeding with the Mallard (Anas platyrhynchos), and although only two cases of hybridisation had been documented in the wild by 1990 (Griffin and Browne 1990) the potential for hybridisation is apparently high, and the wide occurrence of hybrids on O'ahu is testament to this. The bird was eventually extirpated from all the islands as a breeding species except Kaua'i, occasional birds may have wandered to neighbouring islands during the winter or unusual climatic periods.

Kaua'i was probably always the species stronghold due to the high rainfall, large wetland and marsh areas and the large number of low gradient rivers and upland streams. Certainly during the early part of the 20th Century the numbers were reported as being very high with an estimate of 400 Koloa per square mile at the Mana wetlands on the west side of Kaua'i (Schwartz and Schwartz 1953). After the drainage of this area in 1923 the numbers fell dramatically and were estimated at only 5 per square mile a few years later (Schwartz and Schwartz 1953).

Hunting of the species was prohibited for two years in 1939 (Anon 1939) and remained in effect during World War II, after this time the Territory of Hawai'i was allowed to reset the hunting season, however this was never reinstated and the Koloa has been protected from legal hunting ever since. By 1949 the population in the Hawaiian Islands was estimated by Schwartz to be approximately 30 birds on Oahu and about 500 individuals on Kaua'i. Hawai'i, Moloka'i and Maui were believed to be devoid of a permanent population of Koloa. By 1960 it is believed that they were absent from O'ahu also, therefore leaving Kaua'i as the only island with a population of the duck (Swedberg 1967 and USFWS 1994).

O'ahu population

On O'ahu, a captive propagation and release program was conducted between 1958 and 1982 which re-established a population on that island. During this period 326 - 350 birds were released on O'ahu and the population appears to have increased during 1977 - 1987. A total of 300 Koloa was estimated for on O'ahu during this period (Engilis & Pratt 1993 ). The success of these introductions is questionable however, as many of the birds appear to have Mallard traits due to hybridisation after their release into the wild. All Koloa on O'ahu that have been sampled for genetic characteristics have proven to be hybrids (Griffin and Browne 1990).

Hawai'i Population

Birds released on Hawaii appear to be surviving in smaller numbers. Engilis & Pratt (1993) estimated a population of some 200 individuals. They also stated that birds on Hawai'i inhabit more remote streams and ponds than those on O'ahu and therefore would be less likely to come into contact with Mallards and thus were less likely to hybridise.

Maui population

In 1989 the Department of Forestry and Wildlife released a few Koloa on Maui but subsequent data is not available, Engilis & Pratt (1987) doubted however that this would result in a self-supporting population, although there is a small breeding population at present (F.Duvall in pers. comm. to A. Engilis 1996).

Kaua'i population

The individuals present on Kaua'i have managed to maintain a population without supplementation from captive reared birds. Surveys of lowland areas in the 1940's and 1950's estimated 500 birds, Swedberg estimated a total population of 3000 birds in the mid 1960's and Engilis & Pratt (1993) concluded from these figures and waterbird surveys that the Kauai population was probably about 2000 individuals and Telfer in Kato (1981) believed that the total estimated by Swedberg was too high and estimated a population of 1500 to 2000. Many of the birds that Swedberg surveyed and later estimated for were present in high mountain streams which would probably account for discrepancies in earlier accounts and surveys. The fact that Koloa appear to be especially fond of or are forced to use mountain areas has often been overlooked in the literature and in surveys of the species and only in the last few years has the importance been fully realised by biologists, although it was touched upon in earlier reports. Engilis & Pratt (1993) also agree that numbers of Koloa found on annual surveys are below the true total due to their preference for remote streams and bogs which are not surveyed during the counts.

The importance of upland streams to the Koloa is now clear and was obviously well known to the ancient Hawaiians who would engage in hunting trips into the wild interior of the island in search of Koloa (Schwartz & Schwartz 1953, Bostwick 1982). Large concentrations of birds in the past, such as at the Mana wetlands, and in more recent times at locations such as Hanalei probably imply that the species is adaptable to or prefers lowland areas at certain times and has been forced into the more protected, less disturbed interior of the island. It also seems probable that the species is a solitary stream nester but outside the breeding season is comfortable gathering in flocks at a wider range of habitats. Observation of birds in the evening also supports the fact that birds are present in the upland areas in the day and fly down to lower elevations during the night (Perkins 1903, Asquith and Melgar in press).

Although Mongoose do not occur on Kaua'i and hunting no longer takes place; dogs, cats, rats and habitat destruction and disturbance have almost certainly had an effect on the species and its population, although there is little documentation of the impact caused by these threats.

Statewide waterbird counts have shown an increase in Koloa numbers, mostly on Kaua'i, although this could be due to better observer coverage and gathering of birds at favoured sites, where a large flock is easier to observe than a single bird or pair in a stream 10 miles from the nearest path.
Even though Kaua'i has experienced loss of lowland wetland habitat the island still retains a large number of rivers, streams and ditches amounting to over 2,092 miles (Swedberg 1967). Swedbergs census figures show that the majority of Koloa are present in these areas for a great deal of their life; lowland marsh areas are presumably a secondary area that the species uses during times of hardship or when a site can offer more than one of the basic demands required of an area.

The three most basic demands that the species requires are:
1) Feeding areas
2) Loafing areas
3) Nesting areas

All sites may not provide all three requirements and so a number of sites may have to be used to supply all these factors, this would certainly fit in well with movement patterns, both diel and seasonal observed at several sites island-wide.

If the Koloa is to survive on other islands long -term, away from Kaua'i, it has to be realised that the species needs to be able to utilise other habitats as often and as effectively as they use the upland stream and ditch areas on that island. It is essential that research is carried out as to how to entice Koloa into lowland areas and to provide the correct habitat for the species once it is there. Although the previously described areas may account for the majority of Koloa habitat (especially on Kaua'i) it is important to create and manage lowland wetlands which support the species and provide at least some of the basic demands for survival of the Koloa. As Kaua'i possesses the required Koloa habitat for the most part, focus should be turned to creating and increasing populations on other islands, and as these may not have any or as much suitable upland stream areas, the need for optimum lowland habitat should be investigated.

Observing Koloa on Kaua'i

The following locations should provide sightings of the species:

Hanalei NWR, North Shore All year. Best in morning and evenings. Easily viewable from the road and overlooks. Most spend their days at the far west end of the refuge. Numbers range between 100 and 300 birds, with more present during the winter months. Sometimes a few on the river.
Wailua Reservoir, near Kapa'a, East side. All year. Evenings are best, although often distant. Usually between 20 and 30 birds, but numbers fluctuate widely and sometimes none present at all.
Wailua Golf Course Pool, East Side. All year. Early morning and evening best. Small size of pool means that birds are not always present, but up to six may be present. The small size of the pool also means that birds are easily flushed.
Huleia NWR, near Lihue, southeast side. All year. Mornings and Evenings best. Up to 30 may be present, although restricted viewing usually means birds are only seen flying in/out of refuge.
Menehune Fishpond, near Lihue, southeast side. All year. Mornings and Evenings best. Usually about 10 or so present, but sometimes large flocks and often none at all.
Koloa Reservoirs, near Koloa, south side. All year. Evenings best. Numbers vary widely, depending on weather conditions and food availability. Access limited too.
Alexander Reservoir, south side. All year. Evenings best. Birds usually come to feed during the night. Birds may be distant. Four-wheel drive recommended.
Kawaiele State Sanctuary, near Barking Sands, west side. All year. Mornings best. Usually only a couple of pairs. Birds easily flushed.
Mana Wetlands, near Barking Sands, west side. All year. Mornings and Evenings best. Numbers vary depending on water availability. Birds often hard to observe as they spend much time in ditches etc.
Upland Streams, Island-wide. All year, although numbers much higher during the summer. Numbers would be in the hundreds, but actually observing the species before it flushes on approach is difficult.

Most non-population data collected regarding the Koloa tends to be anecdotal and much is now dated. Schwartz and Schwartz (1949) provided limited behavioural notes during their survey of the islands. Banko (1987) provides exhaustive accounts of species distribution but barely touches on the subject of habitat requirements. Engilis and Pratt (1993) concentrated on numbers and general (island) distribution with comments on possible movement patterns. Giffin (1983) provided data and accounts for movements, survival and reproductive success of the Koloa on Hawaii but did not examine feeding requirements in detail.

Swedberg (1969) provides the most authoritative early text on the Koloa, which details the species history, reproduction, behaviour, food habits, range and habitat, abundance and status. Eighteen pages were devoted to the species range and habitat and includes a useful appraisal of different sites around Kaua'i with suitable Koloa areas and details of birds observed. Surveys conducted by Swedberg and the Hawaii Division of Fish and Game resulted in an estimate for the Kaua'i population of koloa. Food habits are confined to just half a page.

The Hawaiian Duck was listed on March 11th 1967 (32 Federal register 4001).

Occurrence of Hawaiian Duck in the Hawaiian Islands.
** Species re-introduced but many/most birds are hybrid Koloa-Mallards (Anas platyrhynchos).
*** Species re-introduced but some birds likely to be hybrid Koloa-Mallard.

Hanalei NWR, Kaua'i. This site holds more

Koloa than any other single site in Hawai'i.


ANON. 1939. Session laws of Hawaii 1939. Act 197. Honolulu.

ASQUITH, A. and C. MELGAR. 2000. Activity of Koloa Maoli in Kaua'i wetlands and their foraging behaviour. Unpublished report.

BANKO, W.E. 1987. Historical synthesis of recent endemic Hawaiian birds. Part I. Population histories - species accounts, freshwater birds: Koloa Maoli. Cooperative National Park Resources studies unit, University of Hawaii at Manoa, CPSU/UH Avian History report No. 12

BOSTWICK, J.M. 1982. Habitat loss and hybridization: the dual threat to the Koloa. Senior Honors Thesis, Department of Zoology, University of Hawaii, Honolulu. 79pp.

BRYAN, E.H. 1939. How Hawaiian birds have been collected and studied. Elepaio 1 96):28

ENGILIS, Jr, A. and T.K. PRATT. 1993. Status and population trends of Hawaii's native Waterbirds,1977-1987. Wilson Bulletin, vol. 105 (1) pp 142-158.

ENGILIS, Jr., A. 1987. Surveys and inventories of waterbirds in the state of Hawaii. Progress report job No. R-III-A, project No. W-18-R-12. Division of Forestry and Wildlife, Honolulu. 48pp.

GIFFIN, J.G. 1983. Abundance and distribution of Koloa on the island of Hawaii. Final report. Pittman-Robertson Project No. W-18-R-7. Job No. R-III-H. 21pp.

GIFFIN.1983. Movements, survival,reproductive success and habitat of Koloa on the island of Hawaii. Final report. Hawaii Division of Fish and Game. Pittman-Robertson Project No. w-18-R-8, Job No. R-III-H. 21pp.

GRIFFIN, C.R. and R. BROWNE. 1990. Genetic variation and hybridization in Hawaiian Ducks and Mallards in Hawaii. Unpublished Report submitted to U.S. Fish and Wildlife Service.

HENSHAW ,H.W. 1902. Birds of the Hawaiian possessions. Thos.G.Thrum Publisher, Honolulu

KATO, T. 1981. Preliminary investigationof Koloa and Mallard hybrdisation. Honors thesis. University of Hawaii Internship program

MELGAR, C.W. 2002. Habitat Creation and Management for endangered Hawaiian waterbirds. PhD thesis in prep. University of Greenwich, U.K. 2002.

MUNRO, J.A. 1939. The relation of Loons, Holbell's Grebes, and Coots to Duck populations. Journal of Wildlife Management No.3. pp339 - 344.

MUNRO, G.C. 1944. Birds of Hawaii. Tongg Publishing Co. Honolulu

PERKINS, R.C.L. 1903. Fauna Hawaiiensis: Vertebrata (Aves). New York: Columbia University Press. 1 (4): 451-461

PHILLIPS, J.C. 1912. A reconsideration of the American Black Duck with special reference to certain variations. Auk 24: 295-306

SCHWARTZ, C.W.and SCHWARTZ, E.R. 1949. The game birds in Hawaii. Board of Agriculture and forestry, Honolulu

SCHWARTZ, C.W. and E.R. SCHWARTZ 1953. Notes on the Hawaiian Duck. The Wilson Bulletin.Volume 65, No. 1

SWEDBERG, G.E. 1967. The Koloa. Hawaii Department Land and Natural Resources, Division of Fish and Game. Honolulu, Hawaii. Unpublished report. 56pp

U.S. FISH AND WILDLIFE SERVICE. 1994. Draft Revised Recovery Plan for Hawaiian Waterbirds. Second revision: Hawaiian Duck or Koloa, Hawaiian Coot, Hawaiian Moorhen and Hawaiian Stilt. U.S. Fish and Wildlife Service, Portland, OR. 96pp.

U.S. FISH AND WILDLIFE SERVICE. 1999. Draft Revised Recovery plan for Hawaiian Waterbirds, second revision. U.S. Fish and Wildlife Service, Portland OR. 107pp

Christian Melgar, Worthing, West Sussex. 2000 - 2002.

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