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Forest bird monitoring protocol for strategic habitat conservation and endangered species management on O`ahu Forest National Wildlife Refuge, Island of O`ahu, Hawai`i.
|Title:||Forest bird monitoring protocol for strategic habitat conservation and endangered species management on O`ahu Forest National Wildlife Refuge, Island of O`ahu, Hawai`i.|
Gorressen, P. Marcos
native bird species
endangered bird species
|Date Issued:||26 Jan 2016|
|Series:||Technical Report HCSU - 026|
|Abstract:||This report describes the results of a pilot forest bird survey and a consequent forest bird monitoring protocol that was developed for the O‘ahu Forest National Wildlife Refuge, O‘ahu Island, Hawai‘i. The pilot survey was conducted to inform aspects of the monitoring protocol and to provide a baseline with which to compare future surveys on the Refuge. The protocol was developed in an adaptive management framework to track bird distribution and abundance and to meet the strategic habitat conservation requirements of the Refuge. Funding for this research was provided through a Science Support Partnership grant sponsored jointly by the U.S.
Geological Survey (USGS) and the U.S. Fish and Wildlife Service (USFWS).
Between 28 February and 17 May, 2011, we established and carried out pilot point-transect surveys at 33 stations within the Refuge. In general, the sampling conditions were good during the surveys. We detected only two native forest birds, O‘ahu ‘Amakihi (Hemignathus flavus) and ‘Apapane (Himatione sanguinea), during surveys, and we did not detect O‘ahu ‘Elepaio (Chasiempis ibidus) or ‘I‘iwi (Vestiaria coccinea) at any time on the Refuge. Abundances of both native species were too low to estimate population densities on the Refuge, but a larger scale survey would likely yield sufficient numbers of O‘ahu ‘Amakihi to estimate their density. We also detected nine alien forest bird species, four of which were observed in sufficient numbers to estimate densities.
Results from the pilot study were used to inform a monitoring protocol designed to track forest bird distribution and abundance on the Refuge. Questions most relevant to management that are addressed by the protocol are: 1) are the distributions of forest bird species changing; and 2) are population abundances changing? Of the two parameters being measured, distribution can be ascertained from point-transect sampling methods for all native and alien passerine forest birds.
On the other hand, the very low abundance of native birds evident during our survey presents a formidable challenge to monitoring population trends over short (annual) to moderate (5-50 year) time scales. To maximize the detection of native birds, we recommend that surveys be conducted during the period of peak bird vocalization, generally from late February to early April. Nevertheless, as a practical matter, it seems unlikely that even greatly increased survey effort will be sufficient to overcome the problem of low detection rates for most native species; thus, we did not develop alert limits that might otherwise be used to trigger actions to arrest population declines. Instead, identifying major factors limiting bird populations and developing methods of reducing threats would seem potentially more useful in guiding management.
The pilot study data serves as a core set of routes/stations for future surveys; however, the sampling effort will need to be expanded geographically to increase detections of uncommon species and to cover a larger, more representative area of the Refuge. The uncertainty in densities ranged from low to very large; thus, detecting trends will be difficult. Increasing the numbers of stations sampled is expected to reduce uncertainty and yield greater power to detect trends. A modest sampling effort, about 90 stations, is likely to produce low to moderate levels of uncertainty for most species, which should allow for detecting large trends (>50% change) in density over long sampling durations (e.g., >50 years). Sampling at this level should provide sufficient detections to quantitatively monitor O‘ahu ‘Amakihi, as well as four non-native birds—Red-vented Bulbul (Pycnonotus cafer), Japanese Bush-Warbler (Cittia diphone), Redbilled Leiothrix (Leiothrix lutea) and Japanese White-eye (Zosterops japonicus). This level of sampling will also provide coverage across the refuge, instead of concentrating the effort in only one portion. In addition to surveying for many decades, conducting the surveys frequently, either annually or biennially, will increase the power necessary to detect trends.
This monitoring protocol can be implemented incrementally while addressing management and conservation needs. This protocol will be most effective, however, when implemented with management actions and research needed to identify the main factors responsible for low population abundances of native species.
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Hawaii Cooperative Studies Unit (HCSU)|
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