Ae`o: Hawaiian Stilt
In traditional Hawaiian society, one of the many ways children amused themselves was by walking on wooden stilts. The stilts were called kukuluae`o and made from `ohe (Reynoldsia sandwicensis) wood.1 Kukuluae`o is also one of the names for the Hawaiian stilt (Himantopus mexicanus knudseni), but the bird is more commonly referred to as the ae`o. The ae`o is one of six native resident waterbirds in Hawai`i. The others are the koloa maoli, Laysan teal, `alae ke`oke`o, `alae `ula, and `auku`u.
The ae`o is an endemic subspecies of the black-necked stilt of North and South America. It is a small, slender, black and white bird with long pink legs. A wader, the ae`o is often seen in shallow water and mudflats foraging for aquatic insects, worms, crustaceans, and small fish. Ae`o nest from March through August in low-lying vegetation adjacent to natural and artificial water bodies. Nests are shallow depressions lined with stones, twigs, and other materials, and the average clutch is four eggs. The downy chicks are tan with black speckling. The adults defend their territories by feigning injury to detract potential predators from their nests and young. They will also give a loud, sharp call and fly nervously around their nests when disturbed.
In traditional times – when the ae`o was common – it was eaten. People caught the birds by pelting them with stones. But populations of the ae`o and other waterbirds declined significantly after Western contact. Prior to humans arriving in the islands, large natural marshes and ponds occurred on most of the main Hawaiian islands. Native Hawaiian construction of fishponds along the coast and lo`i kalo (flooded taro patches) in the valleys resulted in the creation of additional waterbird habitat. Before Western contact, an estimated 25,000 acres may have been in kalo production. Changes in land tenure, the loss of Native Hawaiian land, and major stream diversions resulted in a decline in kalo production and the loss of waterbird habitat. By 1900, approximately 18,000 acres were in kalo production; by 1960, only 510 acres were being cultivated. Many wetlands were eventually filled, and hotels, subdivisions, golf courses, shopping centers, landfills, military bases, industrial areas, and agriculture have taken their place. Extensive wetland losses occurred at Mana on Kaua`i, Kanaha Pond on Maui, marshes in Waikiki, Mo`ili`ili, Moanalua, Kawainui, and Pearl Harbor, and Ka`elepulu and Kuapa ponds on O`ahu.
In addition to the loss of habitat, ae`o are threatened by introduced predators, such as rats, mongooses, dogs, and cats, habitat degradation by invasive plants, diseases, pollution, loss of food sources, and human disturbance. Botulism, caused by a soil bacterium passed on to ae`o through contaminated food sources, kills large numbers of birds during occasional outbreaks. Infected birds are unable to use their legs or wings or hold their heads up, and eventually die. Until around 1940, hunting was yet another threat to ae`o and other waterbirds in Hawai`i.
The ae`o was listed as an endangered species in 1970. The statewide population of some 1,200 to 1,600 birds is considered to be relatively stable or slightly increasing. Ae`o occur on Ni`ihau, Kaua`i, O`ahu, Moloka`i, Maui, Lana`i, and Hawai`i. The recovery of banded birds indicates that some ae`o move between the islands, especially between Ni`ihau and Kaua`i. The first reported occurrence of ae`o on Lana`i was made in 1989 at the Lana`i City wastewater treatment ponds. The Moloka`i population of ae`o appears to be increasing in recent years. Twenty ae`o were observed during the first annual Christmas count of ae`o on Moloka`i in 1989. The number has increased since then to 148 birds observed in 2001. The increase may be due to recent fishpond renovations along the coast and the creation of suitable habitat.
Although ae`o tend to occur in the lowlands, they are occasionally reported from upper elevations. For example, ae`o were observed in June of this year foraging in the Pu`u Wa`awa`a reservoir on Hawai`i at approximately 2300 feet, and they are still occupying this habitat.
One of the core breeding habitats for the ae`o on O`ahu is the Nu`upia Ponds Wildlife Management Area on Mokapu Peninsula. Active management of the habitat and surrounding environment is overseen by Dr. Diane Drigot, senior natural resources management specialist with the Marine Corps Base Hawai`i in Kane`ohe. Mangroves and other invasive plants have been removed from the wetland. Nesting islands for ae`o were created in the middle of the ponds to protect the birds from predators. Marines improve foraging habitat while conducting training maneuvers, predators are controlled, and school children learn about waterbird ecology and plant, weed, and monitor native riparian plants. Over the past 20 years, these efforts have resulted in a doubling of the stilt population at Mokapu from 60 to 130 birds. The base now provides habitat for nearly 10 percent of the state’s total stilt population, as well as 49 additional taxa of waterbirds, seabirds, and shorebirds.
The Corps is also contributing to the recovery of ae`o at a regional level. Sustainable Resources Group International, Inc., has been contracted to prepare a habitat protection plan for the district of Ko`olaupoko (windward O`ahu from Kualoa Point to Waimanalo). The environmental program at Mokapu and efforts by the Corps to help maintain a network of waterbird habitat in Ko`olaupoko are models for effective species conservation in Hawai`i.
1. Hawaiian Antiquities, by David Malo (1951); Hawaiian Dictionary, by Mary Kawena Pukui and Samuel H. Elbert (1986)
— Marjorie Ziegler
Volume 13, Number 2 August 2002
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