April 4th, 2015

Tonight's surprisingly sparse
migration.

Hey everybody,

Oddly enough, though Illinois is experiencing southerly winds tonight, birds aren't moving much. Much of the state is dominated by light migration at best. Why? There are a number of possible reasons for this. The first is that winds are highly unfavorable just south of the Prairie State, and for that reason nothing new is passing into and over Illinois. The second possible reason is that many migrants seem averse to flying in high pressure, a system of which is bringing tonight's southerly winds in the first place. The final possible--though least likely--reason is that many of the migrants we're getting in Illinois are headed northwest, in which case tonight's winds are not very favorable. Whatever the reasons, the mystery of migration makes it exceedingly difficult to do more than speculate about causality. The best we can do is identify patterns, but in the case of tonight, it's clear that there's something at least I am missing. I welcome any of your hypotheses about why birds are less restless tonight!

Tonight's winds. Click to view
live.

All said, it remains possible that migration could pick up later tonight, so let's look at each third of the state:

NORTHERN ILLINOIS:

So far tonight, Northern Illinois is experiencing the least migration of anywhere in the state. Migration there could be called light at best, meaning fewer than 70 migrants per cubic kilometer of sky above. As mentioned above, it remains possible that migrants will start moving later tonight. Regardless of that, there probably while not be very large influxes tomorrow morning, though there may be very slight fluctuation in certain species' numbers.

Looking ahead briefly, winds are forecast to remain southerly throughout the state at least through Monday, so it is almost certain that migration will pick up in that time. Exciting, eh?

CENTRAL ILLINOIS:

Densest concentrations of migration
in the state are visible in Western
Central/Southwestern Illinois

The story in Central Illinois is much the same as in Northern Illinois. That said, given that more migration is happening in Southern Illinois already, heavier movements may extend into Central Illinois later tonight. There are already slightly higher concentrations of migrants overhead in Western Central Illinois than in all of Northern Illinois, so if you're going to be a night-owl tonight, it may be worth checking the radar from time to time. 

Like in Northern Illinois, winds are forecast to remain southerly throughout the state at least through Monday, so it is almost certain that migration will pick up in that time. Exciting, eh?

SOUTHERN ILLINOIS:

As is often the case, Southern Illinois is tonight's happy exception. Though migration could still only be called light at best, more of Southern Illinois is witness to migration tonight than anywhere else in the state. This means that if more birds take off as the night progresses, the radar can only get brighter. In that case, tomorrow's arrivals and influxes will be most apparent in Southern Illinois. If you're going to be a night-owl tonight, it may be worth checking the radar from time to time. This will be the best way to know whether tomorrow will be a significant migrant day.

Like in the rest of Illinois, winds are forecast to remain southerly throughout the state at least through Monday, so it is almost certain that migration will pick up in that time. Exciting, eh?

And there we have it! As always, if you're itching for information on what you may find tomorrow, check out this gloriously helpful page from eBird. If you haven't already, don't forget to check out BirdCast's latest forecast.

With that, I bid you all goodnight. I think we can all look forward to what the next few days of southerly winds may bring (warmer temperatures and birds!).

Note the high pressure system flanking southern IL. It is this system that is driving tonight's winds, and will continue
to give us southerly winds for the next few days.