Population Surveys

MONITORING DEMOGRAPHICS AND POPULATION TRAJECTORIES

POPULATION MONITORING

Mist-netting and Banding

Our team employs a variety of field techniques in order to identify and monitor birds in the wild. One of these techniques is mist-netting and banding. The capture of birds in the wild provides biologists with insight into the health and demographics of the bird species being studied.

“Invisible” mist-nets (so-called because they are as difficult to see as mist) are erected in the forest to capture the birds. Birds are caught either passively or by using playback of their calls to attract them to the net. When the birds are caught in the net, they are carefully extracted and banded quickly and efficiently by trained biologists.

Individuals are each fitted with an aluminum band with a unique numerical combination issued by the US Fish and Wildlife Service. Data are collected on the bird’s health, reproductive status, age, and morphological measurements. From this information, we are able to monitor population changes and individual fitness. These bands have been developed to fit around the birds’ leg like a solid bracelet and do not affect the birds’ lives or mobility in any way after they are released.

Key species are also fitted with an individual combination of three colored plastic bands. Color-banding individuals allows for field identification without recapturing the bird. We use binoculars to view the birds from a far and read the color combination. This is called a re-sight. These re-sights over time help us collect data on survival estimates for individuals, create maps of territories, find nests and pairs, and have more accurate life history information. This is of particular importance in small populations so that we can estimate population size and reproductive success of individual pairs.

Nest and Fledgling Searching

Finding nests and fledglings helps determine a population’s breeding or reproductive success. Our team has spent countless hours trying to find Kiwikiu pairs, their nests, and young. When nests are found, we monitor them to determine their fate (success or failure). If they fail, we try to understand why that happened. This allows us to better understand the limiting factors of the population. What is preventing them from breeding successfully and how can we improve their odds of reproducing? Reproduction is key to stabilizing and growing a population. From finding nests, juveniles, and pairs, we determine the proportion of the Kiwikiu population that are reproducing successfully. This allows us to better understand the Kiwikiu population, so that we can better manage their populations to increase their breeding success and survival.

View Publications page for papers about this research. See Using GIS for an example map of Kiwikiu home ranges.

HAWAII FOREST BIRD SURVEYS

Hawaii is home to one of the most unique and spectacular native bird faunas in the world, but tragically also one the most threatened. Of the 54 historically-known endemic passerines, only 24 are known to be currently extant, of which 14 are listed as endangered by the State and Federal government. An additional ten species that are listed are not currently known from existing populations and have likely gone extinct in the last 30 years. Many forest bird populations are restricted to limited ranges and continue to slowly disappear from even these restricted areas. A few, however, appear to be developing tolerance to avian diseases and have spread into lowland areas. All populations of native forest birds are being adversely affected by avian disease, predation, habitat modification from feral ungulates and invasive weeds, and competition with alien species. Climate change is expected to worsen these conditions as increasing temperatures and drought allow the movement of mosquitoes carrying avian malaria into high-elevation refugia. Management programs are needed to halt the decline in these populations and restore them to safe levels. Basic information on forest bird population status, distribution and trend; and condition of habitats is needed to guide management actions and to provide insight on limiting factors and their control. Once management has begun, data on population trends is essential to evaluate effectiveness of management actions.

Statewide forest bird surveys were begun in the 1970’s by the U.S. Fish and Wildlife Service to obtain baseline information on population status and distribution for all native and introduced forest birds in the state. The Hawaii Department of Land and Natural Resources (DLNR) participated in those surveys and surveys were completed for Hawaii, Maui, Molokai, Lanai and Kauai (Oahu was not surveyed under this multi-agency study). Multi-agency statewide forest bird surveys were resumed in 1988 with DLNR in the lead as coordinator. Forest bird surveys have been completed on all islands, except for Lanai, Kahoolawe, and Niihau, on a rotating basis. These often target areas known to harbor endangered or range-restricted populations. In addition, annual surveys are done on Mauna Kea to document the range and population of the Palila. Continuation of statewide general surveys is needed to evaluate statewide trends in native forest bird species status and distribution, and identify uniform trends, problems and changes in avian community composition.

In addition to general surveys for all forest birds, many endangered forest birds have declined to such critically low numbers that intensive searches are needed to monitor their status and to locate remnant populations to enable initiation of recovery actions. These searches will be conducted as need arises, based on sightings or other evidence that a species may persist in an area.

Approach:

Forest bird surveys will be conducted on each of the five main islands on a five year rotation basis. The order of the 5-year cycle will include East Hawaii (Kau), West Hawaii, East Maui, Molokai and West Maui, and Kauai, in each respective year. Additional sites on these islands and on Oahu will be surveyed as funds allow. Surveys will be conducted in key native forest bird habitat including those Division or Cooperator lands being actively managed to enhance forest bird habitat. Surveys will use the same transect lines established during the statewide surveys in 1988-2000, as well as additional transects needed to fill in range gaps. Transects are laid out following a compass bearing or pre-loaded GPS location data and marked with colored flagging and station tags. All previously surveyed stations have GPS locations and surveyors attempt to count as close to previous stations as possible. Surveying transects or establishing new transects and the periodic maintenance of existing transects involves minimal cutting or clearing of vegetation. Islands with large areas to cover will be surveyed over multiple years such as with East and West Maui and Hawaii.

A variable circular plot census technique and/or other technique to index abundance will be used to survey select areas for status, distribution, and abundance of native and introduced forest birds. Data collected will include date, time and weather condition; species and number, type of observation and distance from observer; plant phenology as appropriate; and ungulate activity index as appropriate. Additional field surveys and observations may be done to collect information on species activity and behavior and reproductive condition. A Variable Circular Plot data analysis computer program will be used to summarize data and calculate population statistics and density estimates. Data entry and analysis may be done by DOFAW staff or contracted out. Survey results and related information on status and management of forest birds will be disseminated to cooperators and the public.

Depending on availability of manpower and funds, additional monitoring may be done to assess habitat status and condition including the presence and abundance of avian diseases, predators, and food resources. Avian diseases will be assessed by monitoring presence and abundance of malaria carrying mosquitoes and/or by surveying resident bird populations for signs of avian disease. Resident birds will be captured in mist nets, sampled for disease (blood and cloacal samples) and released. The presence and abundance of predators will be assessed using snap or live traps. Captured predators will be killed unless marked and released for capture/recapture analysis.

Rare bird searches will be conducted using existing trails and transects or newly established transects. A combination of general reconnaissance, tape call-back, and station counts will be used to locate and determine status and distribution of rare birds. New technologies such as drones or automatic sound recorders (songmeters) may also be used if deemed appropriate. Initial survey contacts will be followed up to locate other resident individuals, delimit territory used, identify key habitat and to search for nests for follow-up habitat and recovery management.

Cooperators in this project include the USGS Biological Resources Division, U.S. Fish and Wildlife Service, National Park Service, The Nature Conservancy of Hawaii and private partners. The Division project leader is the Nongame Staff Biologist in the Honolulu, Administrative Office.

Objectives:
  • To monitor the status and distribution of native and introduced forest bird populations and their characteristics, particularly threatened or endangered species, in selected forest areas throughout the State of Hawaii.
  • To conduct rare bird searches for and find populations of rare and endangered species.
  • To determine status and condition of forest bird habitat including key components such as presence and abundance of avian disease, predators or food resources.
  • Disseminate findings to cooperators and public.
Expected Results:

Information generated through this study will be utilized by the Department of Land and Natural Resources and other conservation-oriented agencies in monitoring status, distribution and population characteristics of forest birds to develop programs for the preservation, enhancement, and recovery of threatened or endangered birds and their habitats including updating and revising tasks and priorities in recovery plans. Data on population size, characteristics, distribution and trend and the status and condition of habitat will be used to assess biological and ecological requirements and limiting factors and identify key habitat areas where ecosystem management actions will be most effective. General surveys and rare bird searches will be used to locate pockets of rare species and nesting birds so that more intensive habitat management, nest protection measures and rear-and-release avicultural techniques can be implemented to manage and recover species on-the-brink.

Surveys conducted in wildlife sanctuaries, Natural Area Reserves, forest reserves, and selected private land where active habitat management programs are being implemented will provide information on population trends and be used to evaluate the effectiveness of management actions. Management actions will be expanded or modified depending on the response in bird populations. Survey information will also provide a data base with which to make assessments and recommendations on potential impacts of proposed land use actions and development projects in areas inhabited by forest birds.

East Maui was last surveyed in the spring of 2017. Read a full report on the last survey here.

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