The Hawaiian duck (Anas wyvilliana) breeds in montane streams and feeds and loafs in lowland wetlands. It historically occurred on all the main Hawaiian Islands except Lana`i and Kaho`olawe which have little surface water. Suitable stream habitats have steadily declined since humans arrived on the islands some 1,600 years ago. Wetlands initially increased due to cultivation of taro and rice, but have been declining in extent since at least the late 19th century. Wetlands and streams have been degraded or destroyed by development, changed agriculture practices, and introduced pigs and goats [1]. Direct impact was caused by human hunting and predation of eggs and chicks by introduced rats, mongooses, dogs, cats, fish and birds. Hybridization with feral mallards that escaped from commercial farms established on Oahu in the 1930s and 1940s continues to threaten the species. Hybridization is also a problem on Kaua`i and Hawai`i.
The Hawaiian duck was fairly common in the 19th century, but was rare in many places and generally declining in the early 20th century [3]. By 1949 it was extirpated from Maui and Molokai, rarely seen on Hawaii, and reduced to just 500 birds on Kauai, 30 on Oahu, possibly some birds on Niihau [1]. By 1962 it occurred only on Kauai [3]. The Kauai population declined significantly between 1956 and 1982 [4]. A state of Hawaii captive breeding program reintroduced the species to the Kohala Mountains on the island of Hawaii in 1958-1980 resulting in a current population of about 200 bird utilizing stock ponds, streams, and the Hakalau Forest National Wildlife Refuge [1, 3]. Hybridization is occurring in both high and low elevation sites [1]. Three hundred and twenty six Hawaiian ducks were reintroduced to Oahu by the state between 1968 and 1980 [3]. The introduction site was occupied by feral mallards and no mallard control program was initiated. Most of the current population is believed to be hybridized, with suspected pure birds declining and suspected hybrids increasing in recent years [1]. The state introduced 12 Hawaiian ducks to Maui in 1989 and 1990, but did not control existing mallard populations [1, 3]. There are currently 20-50 birds on the island, mostly at Kanaha Pond, and most if not all are hybridized [1, 3].
Population estimates between the 1960s and 2000s suggest a relatively stable population but are unreliable due to the majority of birds being located in remote montane streams and hybridized birds resembling pure birds [1]. Biannual summer and winter surveys indicate a population increase between 1967 and 2003, with the Kauai population increasing and others declining due to hybridization [1]. The most recent estimate is of 2,200 birds on Kauai (2,000) and Hawaii (200) and unknown number of pure birds within the 300 Hawaiian duck-like birds on Oahu and 50 on Maui. [3].
Kauai supports considerably more birds than all other islands combined due to its having few mongooses and very low levels of hybridization [1]. The species occurs year round on the Hanalei National Wildlife Refuge and nearby taro fields, though most breeding occurs in montane streams [1]. Use of the refuge increased (first as loafing habitat, later as foraging habitat) due to the creation of impoundments in the 1980s and 1990s and modifications in the late 1990s [1]. The species also uses reservoirs, particularly near Lihu`e and on the Mana Plain [1].
[1] U.S. Fish and Wildlife Service. 2005. Draft Revised Recovery Plan for Hawaiian Waterbirds, Second Draft of Second Revision. U.S. Fish and Wildlife Service, Portland, Oregon. 155 pp.
[2] Engilis, A., Jr. and T.K. Pratt. 1993. Status and population trends of Hawaii’s native waterbirds, 1977-1987. Wilson Bulletin 105:142-158.
[3] Engilis, A., Jr., K.J. Uyehara, and J.G. Giffin. 2002. Hawaiian Duck (Anas wyvilliana). In The Birds of North America, No. 694 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
[4] W. E. Banko 1987. Historical synthesis of recent endemic Hawaiian birds. Koloa-Maoli. CPSU/UH Avian history report 12 B-Pt. 1. Univ. of Hawai‘i, Manoa. |
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