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Huddling for Warmth!
The week brought sightings of at least two "Chimney Swift trees" in which thousands of swifts packed so tightly onto the sheltered side of tree trunks that the trunk is obscured. The birds did this to to thermoregulate: They were huddling for warmth! 

Image: Sylvia Garcia-Smith

Tree trunk covered with Chimney Swifts huddling for warmth.