Pacific Islands Fish and Wildlife Office
Pacific Region
 

Endangered Species in the Pacific Islands

Hawaiian Stilt / Himantopus mexicanus knudseni  / Ae‘o (one standing tall)

Photo of Hawaiian stilt The ae‘o is a slender wading bird that grows up to 15 inches in length. It has a black back and white forehead, and is white below; the female has a tinge of brown on its back. This endangered species has very long pink legs and a long black bill. The Hawaiian subspecies differs from the North American stilt by having more black on its face and neck, and longer bill, tarsus, and tail.
Ae‘o - Photo credit USFWS

Habitat & Behavior:
Ae‘o use a variety of aquatic habitats but are limited by water depth and vegetation cover. Specific water depths of 13 cm (5 inches) are required for optimal foraging. Nest sites are frequently separated from feeding sites and stilts move between these areas daily. Nesting sites are adjacent to or on low islands within bodies of fresh, brackish, or salt water.

Feeding habitats are shallow bodies of water providing them with a wide variety of invertebrates and other aquatic organisms (worms, crabs, fish). They like to loaf around in open mudflats, sparsely vegetated pickleweed mats, and open pasture lands perhaps because visibility is good and. During the nesting period, incubating pairs may move between the nest site and a foraging area.

Stilts have a loud chirp that sounds like: kip kip kip. The female chirp is lower than the male’s.

Past & Present:
Stilts were historically known to be on all the major islands except Lana‘i and Kaho‘olawe. As with the other Hawaiian waterbirds, historic numbers are unknown. It is believed that there were about 1,000 of them in the late 1940s.

The ae‘o can still be found on all the major islands except Kaho‘olawe, but their numbers have not increased by much. It appears that the population has stabilized or slightly increased over the past 30 years. Stilt numbers have varied between 1,100 and 1,783 between 1997 and 2007, according to state biannual waterbird survey data, with Maui and O‘ahu accounting for 60-80% of them.

The primary causes of the decline of this Hawaiian native waterbird has been the loss and degradation of wetland habitat and introduced predators (e.g., rats, dogs, cats, mongoose). Other factors include alien plants, introduced fish, bull frogs, disease, and sometimes environmental contaminants.

The ae‘o can be seen at Hanalei National Wildlife Refuge on Kaua‘i, James Campbell National Wildlife Refuge on O‘ahu, Kakahai‘a NWR on Moloka‘i, and Kealia Pond NWR on Maui, as well as other wetlands around the state.

Conservation Efforts:
The ae‘o was once a popular game bird, but waterbird hunting was banned in 1939. State and Federal effort in protecting wetlands, enforcing strict hunting laws, educating, and working with private organizations and landowners, play an important role in ensuring the livelihood of the ae‘o and many other waterbirds.

The ae‘o was listed as an endangered species in 1967 under the Federal Endangered Species Act. The Hawaiian Waterbirds Recovery Plan was completed in 1978, revised in 1985, and in May 2005 a draft recovery plan was published.

Last updated: September 20, 2012
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