The Pearl Harbor Important Bird Area consists of two units of Pearl Harbor National Wildlife Refuge, the Honouliuli and Waiawa wetland units, which are located on the shores of Pearl Harbor, a large estuary on the southern coast of the island of O`ahu. The Kalaeloa unit of the Pearl Harbor refuge on the Ewa Plain was established primarily for protection of endangered upland plants and is not included in the IBA. The Honouliuli and Waiawa wetland units were established in 1972 as mitigation for construction of the Honolulu International Airport Reef Runway, through cooperative efforts by the Federal Aviation Administration, the State of Hawaii, the U.S. Navy, and the U.S. Fish and Wildlife Service. The refuge is managed by the U.S. Fish and Wildlife Service under a cooperative agreement with the U.S. Navy. The 15-hectare (37-acre) Honouliuli Unit borders the West Loch of Pearl Harbor and the 10-hectare (25-acre) Waiawa Unit borders the Middle Loch of Pearl Harbor. The primary purpose of the wetland units is to provide protection and habitat for four species of endangered waterbirds. The Waiawa Unit is composed of two ponds, one of which is primarily managed for Hawaiian stilts. On-site brackish artesian well water is piped into the ponds for management purposes at the Waiawa Unit. At the Honouliuli Unit, on-site slightly brackish well water is pumped into two ponds. The Honouliuli Unit has greater habitat diversity resulting from fresher water and more gently undulating substrate. The two ponds at Honouliuli can be managed with greater water level flexibility and deeper water levels can be achieved when necessary. Habitats include open water, freshwater marsh, emergent aquatic vegetation, with interspersed mudflats, increasing habitat value for a variety of water-related birds. Both units of the refuge are fenced and neither is open to the general public.
The wetland units of Pearl Harbor National Wildlife Refuge contain one of the largest concentrations of wetland birds in Hawai`i. They are important breeding, feeding, and resting areas for three birds listed under the U.S. Endangered Species Act; the Hawaiian Stilt, Hawaiian Coot, and Hawaiian Common Moorhen. The Hawaiian Coot is an endemic species, while the Hawaiian Stilt and Hawaiian Common Moorhen are endemic subspecies. Maximum numbers of these taxa recorded on the refuge are 389 coots at Honouliuli in December 2002 and 139 at Waiawa in October 1995, 155 stilts at Honouliuli in December 2001 and 259 at Waiawa in September 2004, and 6 moorhens at Honouliuli in January 1999 and 13 at Waiawa in March 1995. The endangered Koloa or Hawaiian Duck was reintroduced to Oahu in the 1960s and formerly occurred on the refuge, with a maximum of 15 recorded at Honouliuli and 8 at Waiawa in January 1999, but hybridization with feral Mallards has become widespread on Oahu recently and most or perhaps all of the birds now using the refuge are hybrids. The Pearl Harbor refuge also supports a variety of migratory waterfowl, shorebirds, and other wetland birds from August-April. Some species occur primarily during migration, but others are present throughout the winter months. Some of the more common migrants are Northern Pintail (115 at Honouliuli in January 2003) and Pacific Golden Plover (622 at Honouliuli in August 2005 and 365 at Waiawa in August 1999). Although these numbers are small by continental standards, they represent some of the largest concentrations of these species in Hawai`i and the Pacific.
The greatest threats to wetland birds at Pearl Harbor National Wildlife Refuge are predation by non-native animals, invasive alien plants, sea level rise, outbreaks of avian botulism, illegal human trespass for fishing and vandalism interfering with water level manipulation, and, for the Hawaiian Duck, hybridization with feral Mallards. Predation by feral dogs, feral cats, mongoose, and rats is a serious threat to waterbirds, especially their nests. Water management and quick response to correct conditions leading to botulism outbreaks (nutrient-rich sediments, high water temperature, low dissolved oxygen, and fish mortalities) have been effective at controlling this potentially deadly disease at Pearl Harbor. Invasive alien plant species, particularly Saltwort (Batis maritima), mangrove (Rhizophora mangle), and Indian fleabane (Pluchea indica), can degrade habitat quality by encroaching and choking wetlands, and require regular control through prescribed burning, water level fluctuation, and mechanical clearing. At the Honouliuli Unit a native plant (Water hyssop, Bacopa monnieri) has also become a problem by sometimes covering large expanses of mudflat and diminishing habitat quality for nesting Hawaiian stilts and wintering shorebirds. The number of feral Mallards on Oahu has increased since Koloa were reintroduced to the island in the 1960s, and hybridization between Koloa and feral Mallards is now common and widespread. Recent changes in regulations have made it illegal to import Mallards into the State of Hawaii, but there already may be no pure Koloa left on O`ahu. Existing feral Mallards should be removed to prevent hybridization and any further genetic introgression into the Koloa population, and it may be necessary to augment the Koloa population on O`ahu with birds from Kaua`i. Global sea level rise and surge from more intense storms could inundate freshwater and brackish coastal wetlands needed by waterbirds.
All of the land comprising Pearl Harbor National Wildlife Refuge is owned by the U.S. Navy and is managed under a cooperative agreement by the U.S. Fish and Wildlife Service.
The wetland units of Pearl Harbor National Wildlife Refuge include open water habitat, freshwater marsh, emergent aquatic vegetation, mudflats, and adjacent upland grassland and shrubland habitats that are dominated by alien plants. Water can be pumped or gravity-flowed into the ponds in order to provide nesting and foraging habitat for waterbirds during the appropriate seasons by using manually operated water control structures.
Pearl Harbor National Wildlife Refuge was established for the conservation of four species of endangered waterbirds, and that continues to be its primary purpose. The refuge is not open to the general public and there are no facilities of any kind. The Honouliuli Unit of the refuge is used by the Hawai`i Nature Center for a highly successful Third Grade Wetlands Education Program under a special use permit. There are periodic volunteer clean-up days to help remove alien vegetation, clear outlet ditches, and repair fences.