Most bird references describe Tree Swallows as “handsome aerialists” because they are such agile aviators and they are a shimmering blueish green. I watched this group of Tree Swallows on a trail at Bombay Hook National Wildlife Refuge. They dart around like little blue acrobats as they catch all kinds of flying insects in the air to eat. Tree Swallows nest either in tree cavities previously constructed by woodpeckers or man-made nest boxes. Bluebird houses with a 1 1/2″ diameter entrance hole are also the perfect size for Tree Swallows to raise a family.