Radar Technology - A Tool for Understanding Migratory “Aerofauna”

Understanding the factors affecting migratory bird and bat populations during all three phases of their life cycle—breeding, non-breeding, and migration—is critical to species conservation planning. This includes the need for information about these species’ responses to natural challenges, as well as information about the impact of human activities that alter resources critical to migrants during passage and stopovers. Birds and bats are also uniquely susceptible to human use of the airspace. Wind turbines, communication and power transmission towers, and other tall structures known to cause bird and bat mortality are being erected or proposed in increasing numbers across the country. In addition, the potential for bird-aircraft collisions poses human safety threats. Management and regulatory agencies, conservation organizations, and industry currently lack this information needed to meet their missions and statutory responsibilities.

Radar Imagery 
This radar image from May 16, 1999, captures the distribution of birds in the airspace shortly after the onset of nocturnal migration near Lakes Erie (left) and Ontario (right). Colors represent logarithmic differences in migrant density; in order of lowest to highest density they are green, yellow, orange, red, and purple. Voids in the radar echo pattern occur over the lakes because most of the migrants are landbirds. Radar echoes caused by northbound migrants can be seen extending over the southern portion of both lakes as birds depart the coastal landscape and fly out over the water. Regions of stronger radar echo this early in the migratory flight show where in the landscape (stopover habitat) birds occurred in high densities prior to the onset of migration.

The biological data available from various radar technologies offer a unique opportunity to learn more about the spatiotemporal distribution patterns, flight characteristics, and habitat use of "aerofauna." The nationwide network of over 150 large-scale Doppler weather surveillance radars (otherwise known as NEXRAD or WSR-88D) provides continental coverage, similar to the scale of migration. Taxa that migrate include landbirds, shorebirds, wading birds, waterfowl, raptors, bats, and insects. In addition, a variety of other radar technologies (e.g., mobile and revised mobile marine radars, airport surveillance radars, military tracking radars, and other pencil-beam radars) and complementary methodologies (e.g., acoustic monitoring, thermal imaging, night-vision monitoring, and visual surveys) can be used to further our understandings of bird and bat migration and to address conservation concerns at a more local or site-specific level.

Recognizing the opportunities presented by radar technologies, the U.S. Geological Survey (USGS), the U.S. Fish and Wildlife Service (USFWS), and university partners collaborated first on individual projects. They then formed a broader, informal “collaborative” to coordinate their radar-related research and work together to develop the suite of products needed for conservation of birds and bats. USGS Fort Collins Science Center scientist Janet Ruth has served as the coordinator for this collaborative effort. Having produced two summary documents (Sojda and others, 2005Ruth and others, 2005) the next objective was to convene a workshop for researchers, management and regulatory agencies, and other interested parties. The focus of this initial workshop (Ruth 2007) was on strengthening the existing USGS–USFWS–university partnership and expanding the collaborative to include new Federal agency partners. The subject matter centered on discussing available technologies, appropriate applications, management-related needs, and ways to strengthen collaborative research and conservation efforts. The ultimate goal of this collaborative is to facilitate and further the use of radar technologies to better understand the movement patterns and habitat associations of migratory birds and other wildlife, and consequently inform wildlife management and regulatory decision-making.

The Use of Radar

LEFT: Radar captures this snapshot of bird migration across the eastern and central United States on April 28, 2004, at 23:02 CDT. Precipitation appears over southern Texas and across parts of the West. Individual radars detect birds out to a certain range, shown as circular patterns of echoes. The overall pattern indicates that birds are migrating as a relatively continuous layer throughout the east-central United States.

RIGHT: NEXRAD (NEXt generation RADar) is also known as Weather Surveillance Radar, 1988 Doppler (WSR-88D). Pictured is the tower that houses the antennae inside the radome (white sphere).

Many technical issues make this collaborative effort challenging: complex data structures, massive data sets, issues of target identity, large areas not covered by weather surveillance radars, model validation, ground-truthing radar data, linking migrants with stopover habitat, and standardization of protocols.  Also, our partners face many biological, management, and regulatory issues concerning the following:

  • tall structures (e.g., telecommunication towers, electric utility structures, offshore oil platforms),
  • wind power,
  • bird-aircraft strikes,
  • habitat protection and identification of key natural and artificial habitats, and
  • effectiveness of management activities.

There is also a need to facilitate better communication among researchers, managers, regulators, conservationists, and industry. However, progress will only be furthered by tackling these issues and challenges. This will involve:

  • facilitating a productive collaboration with Federal management and regulatory agencies and academic researchers as targeted in our first workshop, as well as State agencies, industry, and other interested organizations;
  • building and strengthening scientific capabilities within the USGS, where appropriate;
  • addressing key migratory bird management issues; and
  • promoting full funding for necessary research and development.

One of the action items that was identified and endorsed by the radar workshop participants was to “Create a ‘radar collaborative’ Web site to provide information about radar biology applications, contacts, publications, etc.” As proposed by this action item, this radar science Web site will serve as an initial source of basic radar biology information, with links to applicable Web sites and downloadable files, contact information, an updateable bibliography, and workshop proceedings.

Cooperators: USFWS, USGS, The University of Southern Mississippi.