The Great Lakes Airspace Map - a Decision Support Tool

Mapping migratory bird and bat concentration areas throughout the Great Lakes basin

U. S. Fish and Wildlife Service, R3 Ecological Services

February 4, 2022

An areal photo of the Great Lakes basin, showing all five Great Lakes

Introduction

Birds and bats are important in many ways, including economically and in terms of providing ecosystem services.

For example, bird-watching supports a multi-billion-dollar industry and continues to grow.

Looking for birds (United States Fish and Wildlife Service/Joanna Gilkeson).

Bats are voracious insect eaters and provide ecosystem services by helping to reduce pesticide costs for farmers.

BCI educator shows visitor a bat (United States Fish and Wildlife Service/Ann Froschauer).

photo of educator holding a bat and showing it to a young person

Both also face a variety of serious conservation challenges. North America lost 3 billion birds in the last fifty years ( Rosenberg et al. 2019 publication, PDF). White-nose syndrome has taken a toll on non-migratory bats, reducing populations of some species by 90 percent over the last 10 years ( Cheng et al. 2021 publication, PDF), and migratory bats are impacted by collisions with structures.

Biologist inspects northern long-eared bat with visible symptoms of white-nose syndrome (University of Illinois/Steve Taylor).

photo of a biologist examining a bat that is showing symptoms of white nose syndrome

The Great Lakes basin is known to be important to both birds and bats, but little was known quantitatively about basin-wide concentration areas that could inform conservation priorities. The U.S. Fish and Wildlife Service's (Service) Avian Radar Project was initiated specifically to more fully describe spring and fall migrations and identify areas important to nocturnally migrating birds and migratory and non-migratory bats.

The Radar Project

Migrating songbirds and bats are active at night and therefore can be difficult to study without specialized equipment. To better understand bird and bat activity throughout the Great Lakes basin, the Service, with funding from the Great Lakes Restoration Initiative (GLRI), collected avian radar and bat acoustic data along shorelines throughout the Great Lakes basin during spring and fall from 2011 - 2018.

A picture of targets from the radar unit, that tracks direction of movement. — A radar Trackplot, tracking peak spring migration northward along the shore of Lake Michigan.

The Service used this data to create predictive activity maps, showing areas of high concentration for birds and bats. These maps have been incorporated into a decision support tool. The Great Lakes Airspace Map Decision Support Tool (hereafter, GLAM DST) allows users to overlay bird and bat activity maps with other publicly available or project maps to help resource managers, agencies, and funders plan and implement conservation projects and make on-the-ground natural resource decisions.

Background: Photo of a radar unit for monitoring migratory activity and an acoustic antenna for monitoring bats.

Picture of a radar unit that tracks targets, birds or bats, at night.

Mapping Birds

Each arrow in this map represents a radar location deployed during spring (green northerly arrows, 27 sites) or fall (red southerly arrows, 22 sites) migration. Arrows show the average direction of nighttime flight at each location. Though nightly variation in flight direction can be great, it is generally N/NW in the western basin and N/NE in the eastern basin during spring. During fall, flight direction is generally southward but varies with shore crossing, shore following and shore direction. Zoom in to map on right for a closer look.

Spring Migration

Bright blue on this map indicates areas of relatively high migrant concentration, i.e. areas with high migratory passage and low nightly variation; while areas with warmer colors indicate relatively lower migrant concentration, i.e. lower migratory passage and greater nightly variation in use.

Concentration of spring migration is greater along the western edge of the Great Lakes basin. Migrants in high concentration areas would benefit from 1) protection of the airspace (minimize artificial-light-at-night and collision with structures) and 2) high-quality habitat on the ground for stopover or for emergency landing during inclement weather.

Picture of a migratory bird during spring migration. — Kirtland's Warbler Maumee Bay State Park, Ohio (May 5, 2021, Julio Mulero).

Fall Migration

High concentration areas have shifted east during fall nighttime migration, with bright blue areas centered around south/central Michigan.

Concentration maps have been created for the dawn, day and dusk time periods. During the dawn time period migrants, including birds flying over water, seek lakeshore landing sites, ending nighttime migration. At dusk migrants initiate migration, departing from stopover habitat.

There also are concentration maps for low (less than 1 km) and high (1 to 2.8 km) altitudes. All of these maps are available in the GLAM DST.

A migratory bird during fall migration. — Ruby-crowned Kinglet (September 25, 2010, Putneypics).

Spring Dawn

During the dawn time period, many coastal areas are bright blue, indicating high concentration along lakeshores as birds prepare to end nighttime migration. Warmer colors indicate areas of relatively lower migrant concentrations (lower passage and greater variation among nights).

Fall Dawn

Zoom in to the map on the right to see the bright blue areas, areas predicted to have greater concentration of migrants. Warmer colors indicate lower concentration areas.

Mapping Bats

Bat acoustic monitoring locations are represented by circles with larger circles denoting higher bat concentration sites. The GLAM DST has seven different bat layers grouped by migratory behavior, species, or species groups.

Non-migratory bats (i.e. Myotis species, little brown and northern long-eared bats in this map) have their greatest predicted concentrations (darker blue areas) in the upper Midwest, particularly the upper peninsula of Michigan, northern Minnesota and Wisconsin. Coastal areas also are predicted to have greater Myotis concentrations.

A picture of hibernating little brown bats. — Little brown bats (*United States Fish and Wildlife Service*/Ann Froschauer)

Screenshot of a map showing concentration areas for myotis bats in the Upper Peninsula of Michigan, northern Minnesota and Wisconsin, and particularly in the coastal areas along the Great Lakes lakeshores.

Migratory tree bats (eastern red, hoary, and silver-haired bats in this map) have their greatest predicted concentrations (darker blue areas) along the eastern edge of the Great Lakes basin with, again, concentrations predicted to be greater in coastal areas.

Picture of a migratory red bat resting on a branch. — Red bat (March 10, 2020, Judy Gallagher)

Screenshot of map showing concentration areas for migratory tree bats, these occur along the eastern edge of the Great Lakes basin, especially along the southern lakeshore of Lake Erie. Modeling shows that coastal areas have higher concentrations of migratory bats also.

This map shows concentration areas in darker blue, for all bat species detected.

Places to Protect

Lakeshores - Lakeshores and coastal areas are important for both migratory birds and bats. For migratory birds, lakeshores are important landing sites as nocturnal migration ends and birds look for stopover habitat. Modeling for bats also indicates lakeshores are important, potentially due to an abundance of insects in coastal areas.

Bird migration Trackplots (below) from May 26, 2017, Indiana Dunes, Indiana. Dark blue and purple indicate north/northwest migration (11:30 pm). The shore can be identified as a line running diagonally through both images; a centrally located dot just below the shoreline indicates the location of the radar unit. The image on the right shows a turn towards shore (in yellow) as migrants over water turn to land along the shore at dawn.

Interactive slider image showing Trackplots during nighttime migration — Slide the arrows to compare spring migration (left) and landing at dawn (right).

Interactive slider image showing Trackplots during dawn with migrants turning towards shore to land — Slide the arrows to compare spring migration (left) and landing at dawn (right).

Airspace - Safe airspace is an important component of habitat for migrating birds and bats. Birds and bats are vulnerable to collisions with buildings, wind turbines, cell towers and other structures, leading to mortality. Migratory tree bats are especially susceptible to collision with wind turbines and communication towers. Migratory birds fly at high altitudes at night (e.g., 1 to 2.8 km) though their greatest nighttime density is still, generally, within 400 meters of the ground where they may collide with structures and where they fly within the rotor-swept-zone of wind turbines. In addition, artificial-light-at-night can interfere with birds' ability to navigate, also contributing to collisions with buildings and other structures. Reducing lighting in and around buildings during migration is an effective way to reduce collisions ( Van Doren et al. 2021 publication, PDF).

picture of a farm with wind turbines among the crop fields — Wind turbines (Dori, Wikimedia Commons), urban shoreline (Jamie Bernstein).

picture of an urbanized shoreline at night, large buildings along the shore with lights on — Wind turbines (Dori, Wikimedia Commons), urban shoreline (Jamie Bernstein).

On-the-ground - Creating and protecting high-quality migratory stopover habitat in areas of relatively greater use of the airspace is an important conservation tool. Plantings with native hardwood trees and fruiting shrubs provide cover and host abundant insects for birds and bats and provide nectar via early flowers in spring and high quality fruit in fall for migrating birds. Forest diversity (e.g., mixture of tree age, snags, and stand density) and a fresh water source are beneficial to bats.

a migratory bird eating a caterpillar — Black-throated Green Warbler (Andy Reago/Chrissy McClarren), silver-haired bat (Michele Olson), Red-eyed Vireo (Matt MacGillivray), and a structurally diverse forest (*United States Fish and Wildlife Service*/R. Andrew King).

a bat roosting on a tree trunk — Black-throated Green Warbler (Andy Reago/Chrissy McClarren), silver-haired bat (Michele Olson), Red-eyed Vireo (Matt MacGillivray), and a structurally diverse forest (*United States Fish and Wildlife Service*/R. Andrew King).

Decision Support Tool

The Great Lakes Airspace Map Decision Support Tool, contains the bird and bat layers described previously, along with a number of other relevant map layers. Overlapping different maps allows you to identify areas important for migrating birds and bats that add value to your restoration or conservation projects, enabling conservation dollars to go farther and benefit more species.

This picture shows the predicted concentration of birds at dawn during spring migration along the Saginaw Bay, MI. The bright blue area indicates this is an important area for migratory birds - see legend to the left, showing the relationship between the migrant or "target" passage rate (TPR) and the coefficient of variation (COV). Overlaid on this map are two public map layers, one showing globally important waterbird areas in purple (IBA for waterbirds, Audubon), the other showing protected areas by manager type (green patches, PAD-US).

Background: Screenshot of the DST displaying a radar layer and other public layers.

A screenshot of the Great Lakes Airspace Map with the spring dawn target passage rate displayed, along with an Audubon map of important bird areas and a USGS map of protected areas by manager type. The contents on the map are shown on the left hand side of the picture, displaying a legend within the decision support tool.

Partners

This project was made possible through funding by the U.S. Environmental Protection Agency and GLRI. Thanks also to various state and local parks and private landowners for hosting radar and acoustic equipment and to DeTect, Inc., for technical support.

United States Environmental Protection Agency