Tracking Nēnē Movements Across Park Boundaries

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The federally endangered nēnē, or Hawaiian Goose, once present on most of the Hawaiian Islands, was found only on Hawai‘i Island by 1900. This remnant population was reduced to as few as 30 individuals by 1952 due to the combination of unregulated hunting, introduced mammalian predators, and large-scale habitat degradation. Nēnē have been restored to a few places like Hawai‘i Volcanoes National Park (HAVO) through years of dedicated efforts in captive breeding, reintroduction to the wild, habitat management, and predator control. As their slow recovery has progressed, nēnē have begun to reestablish some natural movement patterns and routes that connect their isolated small subpopulations on Hawai‘i Island.

Nene geese on foggy mountain

A mating pair of nēnē on a foggy day on Hawai‘i Island. Photo: USGS

Overview:

The federally endangered nēnē (Branta sandvicensis), or Hawaiian Goose, once present on most of the Hawaiian Islands, was found only on Hawai‘i Island by 1900. This remnant population was reduced to as few as 30 individuals by 1952 due to the combination of unregulated hunting, introduced mammalian predators, and large-scale habitat degradation. Nēnē have been restored to a few places like Hawai‘i Volcanoes National Park (HAVO) through years of dedicated efforts in captive breeding, reintroduction to the wild, habitat management, and predator control. As their slow recovery has progressed, nēnē have begun to reestablish some natural movement patterns and routes that connect their isolated small subpopulations on Hawai‘i Island.

Map of nene travel routes

Map of nēnē travel routes on Hawai‘i Island. 

There is currently little information about Nene movements between distant Hawai‘i Island populations. Documentation of these movements in conjunction with other land managers is based on re-sightings of individually banded birds outside of expected ranges. Although these sightings are extremely valuable, our understanding of movement activity between established management areas is limited. New field study approaches are needed to determine the routes, timing, and frequency of birds traveling between populations. Importantly, the current gap in understanding leaves Nene vulnerable because potential threats along their movement routes cannot be managed or mitigated. Nēnē that spend seasons outside HAVO may be subject to a suite of threats that reduce their survival.

The recovery strategy for nēnē advocated by the statewide nēnē Recovery Action Group and the Draft Revised Recovery Plan calls for managing an island wide metapopulation by linking small isolated subpopulations. The establishment of an island-wide metapopulation will improve the genetic structure and introduce individuals to new locations, thereby increasing habitat and forage opportunities during periods of food scarcity, while simultaneously reducing the risk of extinction due to catastrophic events such as diseases and severe drought. One strategy is to establish flyways between the different populations: introducing birds to different areas via translocations, and restoring habitat at stop-over locations along their routes. Little information is currently available, however, about which lowland and high elevation subpopulations could best be linked based on movement patterns and the importance of available habitats. A better understanding of these newly established movement patterns and the value of lowland habitats will enable cooperation with other agencies, landowners, and alliances to manage nēnē across their entire range.

Pair of adult nene geese

Pair of adult nēnē. Photo: USGS

Highlights and Key Findings:

The first subject nēnē fitted with a transmitter was from ‘Ainahou Ranch in Hawai‘i Volcanoes National Park (HAVO).  The subject was confined to a pen to protect its two goslings and mate from predators during molt.  Upon release, the subject and its family subsequently flew to Hakalau Forest National Wildlife Refugee (HFNWR) and to the South slope of Mauna Kea, traveling a distance of more than 45 miles.  Two other subjects from HFNWR joined the first subject at the Mauna Kea location after completing molt.  Two additional subjects were fitted with transmitters at the Kahuku Unit of HAVO.

Despite the fact that nēnē are among the most terrestrial of all geese, our subjects have all centered their use around small ponds, wetlands, or water catchments, which are unusual anthropogenic features for nēnē to use given the lack of natural sources of standing water on Hawai‘i Island.  Our subjects also ranged up to 2,512 meters (8,241 feet) in elevation on the slopes of Mauna Loa.  Hawai‘i Island nēnē appear to be recovering some traditional movement patterns lost during their severe population reduction of the 20th century.  For example, subjects have been using locations where nēnē have not been observed for 60 years.  The combined patterns of movements from satellite telemetry and band resights suggest there may be a well-defined flight path between Mauna Kea and Mauna Loa, and an intersection with leeward-windward movements at Kipuka ‘Ainahou nēnē Sanctuary.  Our findings may have major implications for the conservation of nēnē habitat along these routes.

Binomial Generalized Linear Models of meso-scale and fine-scale habitat selection and identified preferred habitat characteristics of nēnē were used.  Meso-scale habitat modeling revealed that nēnē prefer human-modified landscapes during the molting season and higher elevation locations dominated by native shrubland during the non-breeding season.  Fine-scale modeling confirmed results from meso-scale anaylses and revealed nēnē preference for short, sward grasses during the breeding and molting seasons. Understanding nēnē habitat selection throughout the year on an island-wide scale may allow for more comprehensive management planning of this endangered species.