July 5: This evening I happened to be outside at two different spots during the time that blackbirds were flying to roost. Even though these two spots were not far apart, the birds were flying in completely different directions, revealing something of their behavior.
In the town of Oak Harbor, I watched flock after flock of Red-winged Blackbirds, Common Grackles, and European Starlings flying over, all headed south or south-southeast. It was near sunset, and these birds undoubtedly were all flying to a communal roosting site where they would spend the night: possibly in marshes or dense thickets along the Portage River on the south side of town.
Leaving Oak Harbor, we drove to a farmhouse about three miles north of the town. Flocks of blackbirds and starlings were flying over here as well - but here, they were all flying north, or north-northeast. Clearly they were headed to a different communal roosting site than the birds seen just a few minutes earlier.
At this time of year, it's normal for these birds to forage widely in the countryside during the day, and then fly to these communal roosts at night. They may fly a considerable distance to a good roosting site. But somewhere within the first three miles north of Oak Harbor, evidently, there was some kind of divide between birds going to two different roosts.
Something that I don't know, to look into in the future: would these birds always go to the same roost every night, or might some individuals go to alternate sites on different nights?
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