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USFWS Avian Radar Units

Scanning the Skies for Migrants


The U.S. Fish and Wildlife Service operates two mobile avian radar units (Merlin - DeTect, Inc.) that have been stationed around the Great Lakes since 2011. These radar units track birds and bats as they fly through the air. Each radar unit has two antennas that provide different information on how the birds and bats are moving. The radar units cannot distinguish a bird from a bat or identify individual species, so we refer to what the radar tracks as "targets".



Avian Radar UnitPhoto by USFWS

The Horizontal Radar scans out across the landscape and provides a "birds eye view" of what is occurring. It provides information on what direction targets are flying. The relatively large range (about 2 miles) allows it to collect this information from a large number of birds and bats. The large range also allows the radar to stretch out over the water to compare what is happening there with what is happening inland.


The Vertical Radar, sampling perpendicular to the ground, takes a cross section of the airspace and provides standardized counts as well as information on how high the targets are flying. The smaller range (about 1 mile) increases the resolution of the radar so that it can better determine what height targets are flying at. The cross section of the airspace that the vertical radar scans acts like a gate, more reliably counting target that pass through an area. This is why we rely more on the vertical radar counts for an estimate of activity levels.


Radar Properties

The radar antennas on the avian radar units are the same type that are used in marine settings for large boats. Radar waves are emitted from the antennas and reflected back when those waves encounter a solid object such as a bird, bat, tree, house, or boat are recorded and displayed inside the radar unit. Complex algorithms developed by DeTect Inc. automatically distinguish the radar characteristics of birds and bats from trees, planes, insects, and rain. This allows consistent effort and continuous data collection that is not possible with human observers recording data.


The videos below show the raw radar recordings from each of the antennas from near midnight during a time with high migration. These movies are sped up for easier viewing but each new frame update is 3 seconds of real time. The brighter white areas are places where there is a high amount of reflected radar waves. This includes targets that are tracked but also reflections from trees, buildings, and other objects that cause clutter. Clutter is generally stationary and is filtered out by the tracking algorithms. Targets (migrating birds and bats) appear as small circles or ovals moving across the static background.


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Vertical Radar TrackplotHorizontal Radar Trackplot


The targets from the raw radar are tracked by the radar software and summaries are produced for easier viewing. The examples on this site these are 1-hour summaries.


The output from the horizontal radar plots each target and colors it according to the direction it was moving in. For instance, the trackplot displayed on the left shows many targets moving in a southerly direction and are colored red, orange and yellow as a result.


On the vertical radar trackplot displayed on the right, we can see the distribution of flight heights of targets. In this case they are congregated at lower altitudes but some still fly up to 2000 ft. The vertical radar tracks targets up to approximately 9,000 ft in altitude.

Check out our interactive map of various locations we have been, and find out activity using trackplots from your area!

Use of product and company names does not indicate endorsement by the USFWS.


Last updated: October 31, 2017