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Migrating Birds: Overland Migration
Although the spectacle of large and diverse Trans-gulf migrations and fallouts impress so many
birders and ornithologists, large numbers of birds migrate overland over most of the United States. Particularly
heavy migration often occurs in the Great Plains during both spring and fall as large numbers of birds moving to
and from the arctic, boreal Canada and the northern tier states pass. The following images from the early morning of 14 April, 2000 at FWS Dallas-Fort Worth, TX
show moderate to heavy bird migration in progress. Reflectivity values of 20-24 dBZ representing densities of
227-489 birds per cubic kilometer are visible to the west and south of the radar.
Notice an interesting feature in the velocity image - birds at lower altitudes detected closer to the radar
station are moving north, while birds at higher altitudes farther from the radar station are moving northeast
and even east in some areas. Surface winds from the south facilitate northward movement at lower altitudes,
while winds aloft from the southwest and west facilitate movement in more easterly directions. The area of
grayish hues (velocities close to zero) to the east of the radar station visible in the velocity image probably
represents wind-borne particulates and insects.
| Migration peak over Dallas, TX | Complex Vertical wind profile | ||||||||||||||||||||||||||||||||||||||||||||
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| FWS: Dallas/Fort Worth TX (32.57N 97.30W): Base Ref 124nm / Elev=0.5 deg / 1 km²/pixel Clear Mode / VCP 32 04/14/00 08:18 UTC - Max: 45 dBZ | FWS: Dallas/Fort Worth TX (32.57N 97.30W): Radial Vel 124nm / Elev=0.5 deg / 1 km²/pixel Clear Mode / VCP 32 04/14/00 08:18 UTC - Max: -55 kts +58 kts | ||||||||||||||||||||||||||||||||||||||||||||