Yes, weather radar systems are designed to detect the intensity and location of precipitation. Also, since NEXTRAD is based on Doppler radar the velocity of the precipitation (generally moving with the horizontal wind) can also be detected. So with regards to bird migration one can observe both the intensity of the migration, and in which direction it is heading.
Just briefly, in the absence of precipitation these radars use a very sensitive mode that easily detects birds and also insect swarms and bats! It's pretty cool. Song birds migrate preferentially at night, and you can see on the radar images that the birds take off just after sunset leading to an increased signal until about midnight after which the signal decreases again as birds descend. There is an excellent tutorial on radar ornithology
here, which I really recommend reading, particularly to better understand the geometry of the measurements.
Unfortunately the Canadian radars are not as useful, as all signal that is not interpreted as precipitation is generally filtered out.
For southern Ontario and Point Pelee, I recommend using the Cleveland radar,
here. They appeared to have some pretty intense migration down there too last night. In fact those images serve as a good example to illustrate the different appearance of birds and precipitation. The round blob that appears centred around the radar station is birds and the layered feature slowly approaching from the south-west is rain.
You can see radar imagery for any NEXTRAD station
here.
Note that the radar links included in this post will only work for a limited time, as the radar data is only available online for a couple of days.
