Wyoming Ecological Services
Mountain-Prairie Region

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Field Survey Methodology


Data collection should provide a clear understanding of daily and seasonal species abundance, activity patterns, behavior, distribution and habitat use as they relate to proposed wind developments. Surveys should follow established and repeatable protocols (NRC 2007).

Select plots (pre- and post-construction) to be searched through a probabilistic sampling process that allows data extrapolation to the entire wind-energy facility. Variations in topography, vegetation, and other habitat features important to wildlife should be considered in the design. Survey potentially important wildlife areas (e.g., riparian areas, stands of trees, and ridgelines).

We encourage project developers to seek guidance from the WGFD regarding wind development at: http://gf.state.wy.us/index.asp.

Duration and Timing of Surveys

Sampling duration and frequency is dependent on project specific conditions. When estimating abundance, species composition or mortality, an important consideration for sampling frequency, is the amount of variation expected among survey dates and locations.

Conduct surveys throughout the year to account for variation in seasonal wildlife activity. Implement standardized protocols, which are well‐established for estimating avian abundance (e.g., Dettmers et al. 1999). If a precise estimate of density is required for a particular species (e.g., to determine densities of a special‐status species), more sophisticated sampling procedures, including estimates of detection probability, may be needed.


Plan to conduct pre-construction field surveys up to three years to elucidate wildlife use of a site which may vary significantly between years. The duration of pre-construction surveys is dependent upon site characterization and potential wildlife impacts. Project sites located within areas of lower wildlife use may not need to be surveyed to the same extent as those proposed in areas identified as highly important to wildlife.


In order to evaluate the potential effects of the project on species mortality and displacement, monitoring for fatality, abundance and species composition should be conducted. Data should be evaluated in cooperation with Service biologists in order to determine long-term monitoring needs for each project.


Pre-construction Monitoring

Design pre-construction surveys to assess wildlife use of a project area. Include surveys for federally-listed species, migratory birds, and species of management concern. Use existing wildlife data to identify Service’s trust wildlife resources in the area and to determine the types of surveys needed. Information sources include resource agencies, local experts, university or organizational databases, and data gathered at nearby project sites. These resources provide important information but should not replace data collected onsite.

Federally-listed species surveys: Federally-listed species have specific survey protocols. Please work with Service’s Wyoming Field Office to determine survey needs and methods.

Avian activity surveys: Use existing information (data and literature) to identify bird species that occur in the area. While it is important to address all avian species, particular attention should be paid to species that have behaviors, such as flying at the height of the turbine blades or avoidance of vertical structures that predispose them to collision or displacement. Include bird species that winter in Wyoming, such as rough-legged hawks, as well as breeding and resident species.

Diurnal Surveys: Identify temporal and spatial avian activity. For example, identify seasonal variations in behavior, movement directions, flight elevation, and flight path densities. Technologies such as radar may provide detailed data about avian use patterns. Point counts and transect data may be used to estimate avian use and abundance. Selected survey methods need to identify both horizontal as well as vertical (flight height) avian use of differing habitats and topography to help identify the potential for avian activity within the rotor‐swept zone.

Description of the methodologies for avian surveys, such as point counts, line transects, territory mapping, migration counts, vocalization response, roost counts and radar are described in the literature (e.g., Gauthreaux and Belser, 2003; Reynolds et al., 1980; Schaffer and Johnson, 2008). In addition to documenting bird occurrence and behavior, surveys should include measurements of habitat characteristics at the observation point (i.e., covariates that influence avian use such as vegetation and topography) to allow extrapolation of data across the study area.

Nocturnal Surveys: An evaluation of additional risks posed to birds at night should be conducted. If characteristics of the project site and surrounding areas pose a high risk of collision to night migrating songbirds and other nocturnally-active species, conduct nocturnal surveys. Most songbirds and nocturnal migrants fly at altitudes well above wind turbines, but they pass through the zone of risk during ascents and descents and may fly closer to the ground during inclement weather. Nocturnal survey techniques include acoustic monitoring, radar, and night-vision equipment.

Raptor activity surveys: Effective raptor surveys will identify species, abundance, seasonal occurrence, nest and roost activity, forage base, and zones of movement (e.g., between nests or roosts and foraging areas). Assess raptor foraging patterns by surveying and mapping topography and prey bases, such as prairie dog and ground squirrel colonies. Observations should be of sufficient duration, and stratified throughout the day and across seasons to describe area use by raptors.

Raptor nest and eagle roost surveys: Raptor nest surveys provide information to predict risk to local breeding populations, to inform micrositing decisions, and to develop appropriately sized non‐disturbance buffers around nests and roosts. Historical raptor nest data may be available from resource management agencies. This information should be supplemented by conducting raptor nest and eagle roost surveys by both aerial and ground methods which may vary with respect to terrain and vegetation. It is important to identify all intact raptor nests, both active and inactive. Prior to implementation, coordinate with Service, WGFD and/or land management agency biologists to determine the sufficiency of surveys.

Habitat Surveys: Conduct surveys to identify and map habitat and landscape features that are important to wildlife such as riparian areas, rims and saddles of ridges, and prairie-dog colonies. A preliminary review may include use of aerial imagery, topographic maps, and Geographic Information System analyses. Measured features may be based on literature reviews of species’ habitat needs as well as discussions with the Service, WGFD, and land management agency biologists. Features are likely to include, but are not limited to:

  • Riparian areas and water resources (e.g., lakes, ponds, rivers, streams)
  • Forest edges
  • Terrain features such as canyon rims, cliffs, saddles, wind-ward slopes of ridges, isolated trees or rock outcrops
  • Concentrated and seasonal use areas such as rodent colonies or grouse leks, and
  • Raptor nest sites

Bat Surveys: Bats are susceptible to direct fatality from wind energy development; therefore, it is important to thoroughly survey for bats in the project area. Surveys at Wyoming wind energy facilities have documented the presence of almost half of the 18 bat species that occur in the state (Johnson 2005). Migratory, tree-roosting species such as hoary bats (Lasiurus cinereus), and silver-haired bats (Lasionycteris noctivagans) have been disproportionately killed at wind energy developments (Arnett et. al 2008). A state and federal interagency working group is compiling bat conservation recommendations, which will be posted on our website when they are finalized.

Species of Management Concern surveys: Species of Management Concern may have specific survey protocols. Survey needs should be evaluated and coordinated with Service, WGFD, and land management agency biologists to ensure use of appropriate surveys and protocols (e.g., monitoring for bat activity should occur consistently from spring through fall migration).

Post-construction monitoring

Design post construction surveys to assess wildlife impacts from project operation:

Fatality surveys: Monitor mortality at a sufficient number of turbines to provide a statistically robust estimate of project impacts and to identify opportunities for project modification, as needed in the context of adaptive management. The number of turbines monitored can be based on the expected variability in mortality within the project site. Variability in mortality can be estimated from projects with similar conditions within the same region (Morrison et al., 2008). If the project contains fewer than 10 turbines, it is recommended that all turbines be surveyed. The selection of specific turbines to be monitored should reflect movement and avian use of the project area as identified by the pre-construction data. If no specific turbines or turbine strings are identified as more likely to result in mortalities, use a random selection of turbines. Size of search plots should increase with turbine height and diameter of the rotor, using a minimum plot radius approximately equal to diameter of the rotor (NRC 2007).

Intervals between carcass searches depend on carcass removal rates. While a 14-28 day search interval may be acceptable for raptors, small passerine species require a shorter search interval (e.g., < 14 days). Episodic events, such as storms, necessitate daily surveys to evaluate mortality events. Mortality surveys should be comprehensive and inclusive of all size classes of birds.

Include carcass removal and searcher efficiency trials in fatality studies (Anderson 1999, NRC 2007). Carcass counts using different search intervals in areas having different carcass removal and searcher efficiency rates are not directly comparable. Therefore, carcass counts must be adjusted to estimate fatality. Use appropriate surrogates for bat and bird carcasses for assessments of search efficiency and scavenger removal trials.

Avian activity surveys: Conduct post-construction abundance and species composition surveys for comparison with pre-construction data to evaluate species displacement or changes in avian abundance and species composition.

Raptor nests and eagle roost surveys: Identify the activity at raptor nests (spring) and eagle roosts (winter) for a minimum of two years post construction. The need for long-term monitoring should be determined in cooperation with Service biologists.

Species of Management Concern: Species of Management Concern may have specific survey requirements. Please work with our office or the applicable agency to determine the appropriate survey for these species.


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Last updated: April 10, 2013