Satellite Technologies

How do scientists track the movements of birds?

Bird Banding:  Bird banders trap or net birds and place a small, lightweight metal band with a unique number on one leg, and then the bird is released.  The band number, along with the species name, the bird’s approximate age and its sex, and the date of banding, are all sent to a central area in the country where records of all banded birds are kept.  In the U.S., the Department of the Interior keeps these records.  If someone recaptures the bird (or finds it dead or injured) it can be reported to the Dept. of the Interior.  These band “recoveries” could potentially allow scientists to figure out where birds nest and spend the winter, how long they live, and the times, lengths, and routes of their migration.  However, the amount of information a scientist can gather from band recoveries is limited.  For example, if a Peregrine Falcon was banded in Greenland during the breeding season and recaptured in the fall off the coast of Virginia, scientists learn something about the bird's migratory route, but they don't have any information about where the bird stopped along the way, how long it stopped in each area, what habitat types it spent time in, and where the bird is headed next.  To answer these important questions, scientists developed more sophisticated ways to track bird movements. 

Radio Telemetry:  This is a technique used by scientists to track the movements of animals over relatively short distances.  A bird is fitted with a small transmitter that emits a radio signal at a specific frequency, and the scientists make sure that there are no other transmitters being used in that area that are emitting the same frequency.  A scientist can then determine where the bird is spending its time by trying to relocate it with the aid of a receiver and antenna.  The receiver is programmed to pick up the frequencies of the different  radio-marked birds. When the scientist hears the receiver beeping at a particular frequency, she knows that the bird tagged with the transmitter set to that frequency must be nearby.  The closer the radio-marked bird is, the louder the beep.  In this way, the scientist is able to hone in on the location of the bird.  This technique is not useful for determining the movements of animals over great distances, since the receivers can only pick up signals at relatively close distances (usually around 10-20 km). 

Satellite Telemetry:  This technique allows scientists to track the movements of birds over much longer distances, such as tracking them during migration.  A bird is fitted with a transmitter that emits a specific signal that is picked up by satellites rotating around the Earth.  These transmitters are called Platform Transmitter Terminals, or PTTs.  Satellites from the National Oceanic and Atmospheric Administration, which rotate around the Earth, have special instruments on board that are designed to pick up signals from PTTs.  Based on the information contained in the signals, scientists are able to determine the bird's location (to within about 1km) anywhere in the world.  The signals are transmitted from the satellites to receiving stations on the ground.  The signals are then sent from the receiving stations to processing centers, where people archive the data contained in the signals and make the information available to scientists by sending the data through the Internet or on computer disks.  Using this technology, animals can be tracked throughout the year wherever they go on Earth, allowing scientists to solve many mysteries about the migratory routes, behavior, and habitat preferences of birds and other animals.  Right now, satellite telemetry can only be performed on larger birds, since the transmitters are too heavy to be placed on small birds,.  The lightest transmitters weigh about 20 grams, which could be placed on a bird that weighs at least 660 grams.  If the transmitter weighs more than 3% of a bird's body weight, it could hinder its ability to fly.  But scientists are working hard to make the transmitters smaller and smaller so that they may begin to track the journeys of smaller birds. 

To learn more about satellite telemetry, check out the Argos System web site at http://www.argosinc.com.

Weather Radar:  Another innovative way that scientists are tracking the movements of birds is by looking at data from weather and other types of radar stations.  Flocks of birds can easily be seen on certain types of radar, and this type of data provides scientists with information on when major movements of birds occur in an area. Above, you can see a radar image taken by the surveillance radar at Ben-Gurion Airport in Israel, showing a major flock of birds migrating over Israel.