Browsing by Author "Pratt, Thane K."

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    Abundance, distribution, and population trend of the Hawaiian Hawk; 1998-2007.
    (2008-04) Gorresen, P. Marcos; Camp, Richard J.; Klavitter, John L.; Pratt, Thane K.
    The current population size and distribution of the endemic Hawaiian Hawk (or`Io in Hawaiian, Buteo solitarius) on Hawai`i Island was determined as part of a reevaluation of the species’ endangered status. Locations originally sampled in 1998 were resurveyed in 2007 with variable circular plot (VCP) count methods to produce habitat-specific estimates of density and assess trends in abundance. In addition, we developed a method for correcting density estimates for the unobserved movement of hawks attracted to call playbacks. We estimated that the 5,755 km2 breeding range harbored 3,239 hawks (95% CI = 2,610 to 3,868) in 1998 and 3,085 hawks (95% CI = 2,496 to 3,680) in 2007. No significant difference in densities was found among years at either regional or island-wide scales. However, pooled 1998 and 2007 densities did show significant differences among habitats and regions. Our 1998 and 2007 population estimates are as much as twice that of previous estimates, and we discuss reasons for this including differences among studies in the accuracy of distance estimation, accounting for unobserved hawk movement, and the extent of area used for the extrapolation of mean densities. The Hawaiian Hawk appears to persist as a viable population well-distributed throughout forest and adjacent habitats on Hawai`i Island. However, with a population comprised of about 3,000 individuals confined to a single island, the species is vulnerable to the effects of human-caused change to its habitat base.
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    Population trends of native Hawaiian forest birds, 1976-2008: the data and statistical analysis.
    (2009-11) Camp, Richard J.; Gorresen, P. Marcos; Pratt, Thane K.; Woodworth, Bethany L.
    The Hawaii Forest Bird Interagency Database Project has produced a centralized database of forest bird survey data collected in Hawai`i since the mid-1970s. The database contains over 1.1 million bird observation records of 90 species from almost 600 surveys on the main Hawaiian Islands—a dataset including nearly all surveys from that period. The primary objective has been to determine the status and trends of native Hawaiian forest birds derived from this comprehensive dataset. We generated species-specific density estimates from each survey and tested for changes in population densities over the longest possible temporal period. Although this cumulative data set seems enormous and represents the best available information on status of Hawaiian forest birds, detecting meaningful population distribution, density, and trends for forest birds in Hawai`i has been difficult. These population parameters are best derived from long-term, large-scale, standardized monitoring programs. The basis for long-term population monitoring in Hawai`i was established by the Hawaii Forest Bird Survey of 1976-1983 (Scott et al. 1986). Since then, however, only key areas have been resurveyed, primarily to monitor rare species. The majority of surveys since the early 1980s have been conducted by numerous, independent programs, resulting in some inconsistencies in methodology and sampling that in some cases has been intermittent and usually at limited scale (temporally or spatially). Thus, despite the consolidation of data into a centralized database, our understanding of population patterns is rather limited, especially at the regional and landscape scales. To rectify their deficiency, we present a framework to improve the understanding of forest bird trends in Hawai`i through an overarching monitoring design that allocates sampling at appropriate regional and temporal scales. Despite the limitations of the current monitoring effort, important generalities stand out vividly from the multiplicity of species-specific trends. Overall, in marginal habitats the Hawaiian passerine fauna continues to decline, with populations of most species shrinking in size and distribution. Since the early 1980s, 10 species that were rare at the time may now be extinct, although one, the `Alalā (Corvus hawaiiensis), survives in captivity. Dedicated search effort for the remaining nine species has been inadequate. Of the 22 species remaining, eight have declined, five appear to be stable, two are increasing, and the trend for seven species is unclear. On the bright side, native passerines, including endangered species, appear to be stable or increasing in areas with large tracts of native forest above 1,500 m elevation, even while decreasing in more fragmented or disturbed habitats, particularly at lower elevation. For example, all eight native species resident at Hakalau Forest National Wildlife Refuge have shown stable trends or significant increases in density over the long-term. Thus, native birds are ever more restricted to high-elevation forest and woodland refugia. It is these upland habitats that require sustained and all-out restoration to prevent further extinctions of Hawaiian forest birds.
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    Rare and endangered species of Hawaii Volcanoes National Park
    (2011-12) Pratt, Linda W.; Pratt, Thane K.; Foote, David
    Hawai`i Volcanoes National Park (HAVO) is the largest area in the State of Hawai`i protected for its geology and landscapes and its native flora and fauna. The park covers approximately 135,000 hectares or 333,000 acres in all. These lands stretch from the seacoast of Kīlauea Volcano to far above timberline on the summit of Mauna Loa (Figure 1). This vast area includes expanses of forests, woodlands, shrublands, and barren lava flows that represent an array of native ecosystems. Contained within these communities are a great many species of rare animals and plants, most of them unique to the island of Hawai`i, and some of them surviving only in the park. These are the biological treasures of Hawai`i Volcanoes National Park. Our book is a guide to all animal and plant species in HAVO that are specially recognized as endangered species in the general sense. (The official designations at four levels and the unofficial designation of species of concern are explained later.) There are 23 such animal species and 71 plant species covered in the handbook, including six species planted in HAVO but not naturally occurring. In addition, we describe seven rare communities. In some cases, HAVO offers the best opportunity to save these species and communities from extinction. Increasingly, the park has attempted to restore rare populations by conducting surveys to locate them, controlling threats such as feral livestock, and bolstering existing populations or creating new ones by planting nursery stock. To aid such efforts, our original intent was to publish an identification guide for researchers and field management personnel. Particularly, we wanted to familiarize the reader with the many rare plant species which otherwise are known mainly from the technical literature. Because we soon came to realize that this handbook would be useful to a much larger, general readership, our aim is to make this information available to anyone interested in endangered animals and plants at Hawai`i Volcanoes National Park.
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    Status and trends of native birds in the Keauhou and Kilauea Forest, Hawai`i Island.
    (2010-05) Camp, Richard J.; Jacobi, James D.; Pratt, Thane K.; Gorresen, P. Marcos; Rubenstein, Tanya
    A Safe Harbor Agreement (SHA) is a voluntary arrangement between the U.S. Fish and Wildlife Service and non-Federal landowners to promote the protection, conservation, and recovery of listed species without imposing further land use restrictions on the landowners. Kamehameha Schools is considering entering into a SHA for their Keauhou and Kīlauea Forest lands on the island of Hawai′i. Bird surveys were conducted in 2008 to determine the current occurrence and density of listed species for the Keauhou and Kīlauea Forest, a prerequisite for establishing an agreement. Because of different management practices in the proposed SHA area we stratified the survey data into intact and altered forest strata. The listed passerines—′Akiapōlā′au (Hemignathus munroi), Hawai′i Creeper (Oreomystis mana), and Hawai′i ′Ākepa (Loxops coccineus)—occur in both strata but at low densities. The endangered ′Io (Hawaiian Hawk; Buteo solitarius) also occurs within both strata at low densities. This report was prepared for the U.S. Fish and Wildlife Service and Kamehameha Schools to provide information they can use to establish baseline levels for the SHA. In addition, we describe the status and trends of the non-listed native birds.