Migrating Birds

Radar Probes
Keweenaw Bird and Bat Migration

For four years the U.S. Fish and Wildlife Service (USFWS) Avian Radar Project has installed mobile radar units at various locations near Great Lakes shoreline. These units along with acoustic monitors placed nearby are tracking birds and bats as they migrate.

Two out of the four great migration pathways in North America pass through the Great Lakes basin. Great Lakes shorelines are where the most stopover habitat is located. Even if the migrants continue inland from over the lake to other habitat, they must travel through the area along the shoreline. These shoreline areas are critically important to migrants. 
The purpose of Avian Radar Project is to find when, where, at what altitude, and under what conditions bats and birds migrate. The data collected will help the USFWS better advise about wind energy development—identifying when and where wind turbines present high risk to these migrants. The mobile radar units are stationed within a few miles of shoreline in off-the-beaten-path locations. Because of the expense and vulnerability of the equipment, the exact location of the units is not publicized. From early September to mid-November one of the avian radar units and acoustic monitors was placed in Keweenaw County.

The Avian Radar Unit has two long rotating radar antenna bars. The radar is like radar used on large boats. Radar waves emitted are reflected back when they encounter a solid object. Algorithms have been developed to distinguish birds and bats from such things as insects, planes, and rain. Images reveal the path of flight, duration of flight, and altitude of migrants passing through the radar beams. The data is automatically stored for later analysis.

The horizontal radar with about a two-mile range scans across the landscape and shows the direction in which the individual birds and bats are flying. The large range also allows the radar to stretch out over the water (when positioned inland about 0.75 miles) to compare what is happening there with what is happening inland.

Bird Migration Facts

Fat is normally only 3 to 5% of most birds’ body mass. However, before migrating birds bulk up. This gorging behavior is called hyperphagia.

Some birds nearly double their weight before they embark by storing excess calories as fat. A ruby – throated hummingbird can store enough fat to fuel a 24 hour non-stop over Gulf of Mexico! That’s approximately 600 miles.

Birds migrate at speeds up to 50 miles per hour.

Songbirds tend to migrate at night in part using the darkness to avoid predators such as hawks.

Raptors, cranes, ducks and geese often migrate during the day when they can take advantage of thermal air currents.

Birds’ visual flight map aids are landforms, the location of the sun, and the position of certain stars and patterns of stars at night. It is thought that these visual cues are learned in the first year.

Birds have magnetite grains above their nostrils. It is believed this mineral helps birds navigate using the Earth’s magnetic field.

Estimates suggest only 50% of birds flying south in the fall survive to return to breed the following spring due to predation, habitat loss, adverse weather, and collisions with buildings, wind turbines, communication towers, and power lines.