Here are five radial velocity radar images from the Gulf Coast today at around 12:30 pm. With a south wind, this is about the time most birds arrive after crossing the Gulf. Don't forget, however, that a lot of birds are circum-Gulf migrants - they fly northward around the east coast of Mexico instead of crossing water. A sixth image show percipitation at Oklahoma City for comparison.
Let's follow the radar around the Gulf:
Below is radar at Brownsville, TX on the Mexico border. Note the northward movement of "stuff" parallel to the coast. The scale on the right indicates the speed of any objects moving. This should be compared to the wind speed. The radar displays from ground level at the station, to around 10,000 ft. at its limit - 130 miles. Most migrants under these conditions would be flying at about 4,000 ft. The winds at Brownsville and Corpus at this altitude were about 30 kts, which explains the dark colors. Birds flying would be measured at 30 kts, plus the speed of the bird.
Further up the coast at Corpus Christi, still paralleling the coast:
At Houston, showing the typical pattern of direct flight from the Gulf. The wind speed was 7 kts - notice how much faster the "objects" here are moving.
Notice as we go eastward, the number of birds diminishes greatly. At New Orleans:
One last velocity image for comparison from Oklahoma City showing thunderstorms moving north northeast.
There you have it. If you'd like to check the images yourself anytime, they can be found Here .