|Tonight's unexpected but not unwelcome|
So at this point, we have reached an important threshold. It is a point that I will, in my high level of scientific sophistication, term "birds-too-sick-of-sitting-around-not-to-migrate-ism". Whether or not this is actually the case, it's starting to get cold. And birds are responding. Even Saturday night, when winds were predominantly southerly throughout much of the state, moderate migration was occurring. Tonight, a similar story is developing; winds are predominantly westerly with an unfavorable southerly tinge to it in many places. Regardless of that, the radar is even green in some places, indicating moderate to heavy migration! Looking at specific radar stations around Illinois, we can see the migrants are moving southeast with the westerly winds.
So what could be the causes of this? In the realm of insectivores, which most neotropical migrantsare, food gets scarcer and scarcer as average temperatures drop. It also takes much more energy to maintain body heat during the night. In effect, if migrants don't make it south, they're daily energy demands double at a time when energy sources are halving or disappearing entirely.
|Red colors means the birds are moving away from the|
radar station, blue means they are moving toward, and
the grayish division between the two is perpendicular
to the birds' direction of travel
I think this sense of urgency has been causing the migration seen the past couple of nights. We still have a lot to learn about migration, but an interesting question is this: would migrants be moving in such large numbers tonight if the temperatures were warmer? It's hard to know for sure.
Regardless, expect influxes of about everything possible tomorrow, throughout the state. This means the last of the thrushes, later-migrating warblers like Yellow-rumpeds, Pine, Palm, and Orange-crowned, and especially sparrows. Expect peak influxes of Nelson's Sparrow to continue at least for the next week. Raptors should also be a big part of the story tomorrow, with falcons, later hawks, and hopefully that White-tailed Kite in Wisconsin moving south to our hawkwatches. Anytime now, as our Indian Summer comes to a melancholy close, waterfowl variety will begin growing with the arrival of diving ducks back into our state.
Overall, according to the radar, the going's good in Illinois. The wind forecast, which predicts westerly winds through tomorrow and then southerly winds, seem to be becoming less relevant as birds have been migrating regardless of these conditions, so here's hoping for the best.
Awesome. Good luck, everyone.