ARTICLES ON HAWAIIAN BIRDS AND BIRDWATCHING AND OTHER PACIFIC WILDLIFE

The Laysan Duck (Anas laysanensis)

The Laysan Duck (Anas laysanensis) is endemic to the Hawaiian Islands and is currently restricted in range to the island of Laysan in the Northwest Hawaiian Island Chain, but was once the most widespread of the native ducks on the Main Hawaiian Islands and sub-fossil records indicate that they also occurred on some of the other Northwestern Hawaiian Islands, such as Lisiansky. Twelve Laysan Duck were released by the U.S. Fish and Wildlife Service on Pearl and Hermes Reef in 1967 but none were reported after 1967 (Sincock and Kridler, 1977, Berger 1981).

The species is an island derivation from the Holarctic Mallard (Anas platyrhynchos), an irregular winter visitor to the Hawaiian Islands. The status of Mallards and their wild occurrence in the Islands in recent history has been clouded by the large numbers of escaped and released birds, which have taken to hybridising with the endemic Koloa (Anas wyvilliana), and only a handful of individuals deemed wild occur each year, although numbers occurring in historic times was likely much higher. On Laysan the only records of Mallard up to December 31st 1973 were as follows; one collected on 7th November 1896, a pair from December 22nd 1912 - February 1913 when collected and a drake seen on 18th March 1968.

Warner (1963) stated that "The high degree of endemicity of the flora of Laysan, seven endemic varieties of twenty-six recorded species (Christophersen & Caum, 1931), and of insect life strongly suggests that a rather protracted period of stability preceded the island's invasion by white men. The unusual nature of the vegetation, which included groves of endemic sandalwood trees (Santalum cunceatum var. laysanicum) and several prichardia palms, Prichardia sp?...both plants now extinct, further distinguished Laysan from the rest of the sand and coral islands at the northwest end of the chain. These generally have a rather simple flora with fewer endemics."

Individuals were killed for food on Laysan and sport by the early guano collectors, but were protected to a degree by some Island managers. In 1902 the population was estimated by Fisher as being under 100. During the feather raids of 1909 and 1910 more birds were killed for food and feathers and Dill and Bryan estimated that in 1911 only six or seven adults and five young had survived, the following year Bailey counted a total of just seven birds. It was also reported that just one female survived at one point and all the eggs from the nest were destroyed by a Bristle-thighed Curlew, but apparently the female managed to lay another clutch and all the eggs survived, if this is true then the species had a miraculous escape from complete annihilation. The population was not only under pressure from hunting but also from introduced rabbits, which had decimated the vegetation of the Island and had resulted in terrible erosion of the soil, in less than two decades. Eradication of the rabbits was attempted in 1912 and 1913 but failed, although this may have provided some respite. By the end of 1913 nearly no vegetation was left. At the same time Guinea pigs and domestic pigs were introduced and these also uprooted and ate large quantities of vegetation.

Figure 1. Laysan Island showing the large central saline lagoon.

Topographic data in part from "Tanager" Expedition, 1923. Beach morning-glory association includes the entire plant species complex found on and adjacent to the lake flat. The sand-filled depressions are believed to be former fresh water ponds.

By 1913 Munter counted 13 on the freshwater pond during a brief survey during on April 3rd, and 18 birds were recorded by Schlemmer on July 26th of the same year. In April 1923 Wetmore counted 23 individuals. By this time the freshwater pond had filled with drifting sand and dust and even the saline lagoon had started filling with sand. The future of the species was in doubt as few birds remained and the remaining habitat was slowly disappearing - the Laysan Duck seemed to be quickly heading for extinction.

In 1923 another eradication was attempted and was more successful, with almost 100 percent of the rabbits being wiped out. There was still little vegetation left and the last few rabbits died out between 1923 and 1926. During the years when most of the vegetation had been destroyed a few small areas of sesuvium were left standing and the Laysan Duck used these areas as cover and for foraging, however once the vegetation elsewhere on the island started to regrow the sesuvium was completely ignored as a food source.

The vegetation started to recover on the island by 1930. The population of ducks slowly started to increase:

1936 - 11 birds seen

1950 - 26 adults and two broods seen

1951 - 39 birds seen

1957 - 22 adults seen and population estimated at 580 to 740 birds

1958 & 1961 - Population estimates of 600 to 700 birds

1973 - Population estimated at c. 700 birds

1979 - 1980 Population estimated at 510 birds

1986 - 1987 Population estimated at 500 birds

1991 - 1992 450 birds observed

1994 - Population considered to be less than 100 adults

1995 - Population risen to 246 adults

2000 - Population estimated at c.500 individuals

The number of birds seen and the population estimates vary widely due to the fact that most birds spend the day out of view under vegetation.

Figure 2. Graph showing estimated population size of the Laysan Duck during historical times, based on published records and transect censuses. Precise nature of growth since 1923 speculative. Authorities and year of census as indicated by numbers on graph. 1. Fisher, 1902; 2. Dill & Bryan, 1911; 3. Bailey, 1912; 4. Wetmore, 1923; 5. Coultas, 1936; 6. Brock, 1950; 7. Brock, 1951; 8. McKernan, 1955; 9. Warner & Woodside, 1957; 10. Warner & Rice, 1958; 11. Warner and Party, 1961. Above left photo and graph at left taken from Warner 1963.

Current status

Restricted in the wild to Laysan Island in the Northwestern Hawaiian Islands. Laysan lies 1,463 kilometres WNW of Honolulu, O'ahu at 25 degrees 46' N,171 degrees, 44'W.

The current population is about 500 individuals. Moulton and Marshall (1996) state, "In fall-winter 1991-1992, as many as 450 observed during counts; followed by reproductive failure and discovery of abnormally large number of dead (48) from August to December 1993. By early 1994, population thought to be <100 adults, but by late 1995 weekly counts had risen to as many as 246 adults (M.Webber pers. comm). Drought, very low water level in lake, related shortage of brine flies, perhaps in combination wit a nematode infestation, may have caused population decline. Total reproductive failure, presumably owing to drought and scarcity of brine flies, also occurred in 1987. Very high water level in lake, and presumably abundant brine flies, in 1994-1995 resulted in extended reproductive season with unusually large number of ducklings observed".

The present estimated number of five hundred individuals is probably the carrying capacity of the island.

Habits and Behaviour

Feeding: The main food taken by the ducks is macroinvertebrates which the birds find in the littoral zone of the lake, in shallows and on the mudflats, as well as in sand under vegetation. Birds will run through swarms of adult brine flies with their neck out-stretched and their bill held open low to the ground. The birds snap up the brine flies with sidewards head movements. Ducks will also feed on larvae and pupae of noctuid moths which they find under vegetation and in sand, as well as feeding on fly larvae in the lake by dabbling and sifting with their bills. Occasionally they will feed on invertebrates found under dead seabirds. The majority of feeding and drinking is undertaken at the lake at dusk and at night, with birds sheltering under vegetation during the heat of the day.

Locomotion: The species walks and runs very well and usually uses this method to escape, rather than flying. The pelvic girdle is adapted to a terrestrial existence and the leg skeleton has a long femur and short middle toe, both which represent some loss of ability to swim, but enhanced ability to walk and run. Birds do still use the lake for swimming in though, especially if crossing from one feeding area to another or during pair-bond formation. Occasionally recorded swimming on the ocean. The species regularly flies in order to reach other areas of the island, although Marshall (1989) recorded that adults were observed flying <1% of the time. Apparently the skeletal dimensions of the wing have undergone reduction relative to the Mallard and exceed those changes in the Hawaiian Duck (Livezey, 1993). Further signs of wing reduction is the frequent lack of full complement of primary remiges. Drinking occurs at freshwater seeps by taking water into the bill and raising head to swallow.

Breeding: The male does not establish a territory but defends the female during the pre-nesting and laying periods, whilst the pair is feeding and drinking at communal areas. A temporal, mobile territory is based upon the dominance among pairs, and there can be vigorous competition for limited resources, such as freshwater.

Predation: No real threats to the species on this isolated site, although Laysan Finches do crack the shells and eat the contents of some Laysan Duck eggs.

Future for the species

The future for the Laysan Duck is unclear at the moment. The population on Midway is very susceptible to extinction through disease, drought or some other factor and so it is clear that further populations are needed to ensure the continued survival of the species. A few birds are kept in collections and zoos and these may help to increase numbers eventually, however a further population should be created in the wild. It has been mooted that birds should be released on Kaua'i, as this species was once common there, but it is unknown what effect this would have on the native Koloa or other endemic waterbirds. It has been proven time and time again that alien species have a devastating effect on Hawai'i's habitats and endemic species - would the re-introduction of a once common endemic have the same consequences? Consideration also has to be given to the Laysan Teal themselves. Could they cope with other species? Could they find enough food? Would they be even more susceptible to disease on other islands? Would they hybridise with Mallards or Koloa ? Also some birds kept in captivity have shown increased amounts of white feathering on the head, which seems to increase the longer a bird is held, and some birds have become almost entirely white. There are many factors to consider before relocation can be attempted of this enigmatic and unusual Duck.

Thanks to Mark Rauzon for the use of the fantastic Laysan Duck photograph from his book Isles of Refuge - Wildlife and History of the Northwestern Hawaiian Islands. (University of Hawai'i Press, Honolulu. 2001.)

References:

BERGER, A.J. 1981. Hawaiian Bird life. 2nd ed. University of Hawaii Press, Honolulu.

COLLAR, N.J., M.J. Crosby and A.J. Stattersfield. 1994. Birds to Watch 2. The World List of Threatened Birds. Birdlife International, U.K.

DILL, H.R. and W.A. BRYAN. 1912. Report of an Expedition to Laysan Island in 1911. U.S. Department of agriculture Biological Survey Bulletin 42.

ELY, C.A. and R.B. CLAPP. 1973. The Natural History of Laysan Island, Northwestern Hawaiian Islands. Atoll Research Bulletin No. 171. The Smithsonian Institute, Washington D.C.

FISHER,W.K. 1903. Birds of Laysan and the Leeward Islands, Hawaiian Group. U.S. Fish Comm. Bulletin. No. 23.

LIVEZEY, B.C. 1993. Comparative morphometrics of Anas ducks, with particular reference to the Hawaiian Duck Anas wyvilliana, Laysan Duck A. laysanensis, and Eaton's Pintail A. eatoni. Wildfowl 44: 75 - 100.

MADGE, S. and H. BURN. 1998. Wildfowl - An Identification Guide. Helm, Kent.

MARSHALL, A.P. 1989. The behavior of Laysan Ducks (Anas laysanensis) in captivity and on Laysan Island. Ph.D. diss.,Ohio State University, Columbus.

MOULTON, D.W. and A.P.MARSHALL. 1996. Laysan Duck (Anas laysanensis). In The Birds of North America, No. 242 (A.Poole and F.Gill, eds). The Academy of Natural Sciences, Philadelphia, PA. and The American Ornithologists' Union, Washington, D.C.

MOULTON,D.W. and M.W. WELLER. 1984. Biology and Conservation of the Laysan Duck (Anas Laysanensis). In The Condor, Volume 86, No.2. The Cooper Ornithological Society.

MUNTER, W.H. 1915. Report of destruction of bird life on Laysan Island. Annual Report. Coast Guard for 1915.

SCHLEMMER, M. and E.L. SCHLEMMER. 1915. Copy of the log of the yacht "Helene" and diary written on Laysan Island from June 25 to December 2 1915. Rec. Group 22, U.S. National Archives.

SINCOCK, J.L. and E. KRIDLER. 1977. The extinct and endangered endemic birds of the Northwestern Hawaiian Islands. Unpublished manuscript, U.S. Fish and Wildlife Service, Honolulu.

WARNER, R.E. 1963. Recent History and Ecology of the Laysan Duck. In The Condor, Volume65, No.1. The Cooper Ornithological Society.

Christian Melgar. Worthing, West Sussex, UK. 2002.

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