Tracking Bird Migration on Weather Radar
Radar technology allows us to experience the mystique of bird migration at night. It also serves as a useful tool for the study of bird migration patterns and behaviors, as well as alerting us to any changes in those patterns and behaviors.
How Radar Works
Radar is essentially a tracking system that is used to detect the location, speed, direction and altitude of an object. Common uses of radar include weather system detection, air traffic control and navigation, marine traffic control and navigation, monitoring vehicle speeds on roadways and monitoring the migration patterns of birds, insects and other animals.
The two main components of a radar system include a transmitter that emits pulses of energy into the atmosphere at regular intervals, and a receiver that captures any reflected radar energy. Radar energy gets reflected when it “bumps” into a solid object in the atmosphere. The larger the solid object, the higher the value of the reflected energy; for example, a raindrop produces a higher reflected energy value than a unit of drizzle, and a bird produces a higher reflected energy value than an insect.
Radar operates in two modes: Clear Air Mode and Precipitation Mode. When there is no significant precipitation detected within the range of the radar, it is switched into Clear Air Mode. This mode is used to detect changes in the atmosphere, called “echoes” that are unrelated to precipitation (outside of extremely fine moisture particles).
In Clear Air Mode, the radar’s antenna spins more slowly which dramatically increases the sensitivity and resolution of the radar. It can detect objects so small (e.g., dust particles) that they are reported in terms of negative values.
Bird and insect migrations are detected using Clear Air Mode. The radar images of these migration echoes can be striking in their intensity and provide valuable information for biological research.
Radar Image of Bird Migration
The animated picture on the left, below, illustrates a series of radar images from a heavy night of bird migration through Toronto, Canada. The vertical chart on the right provides a color key for reading the patterns on the radar image.
Click here to read more about the radar detection of bird migrations.