Tree Swallows (Passeriformes: Hirundinidae: Tachycineta bicolor) spend their summers breeding in the northern half of North America. They nest in tree cavities and wooden boxes provided by humans, usually near bodies of water. Ponds, lakes, and streams can produce large numbers of dragonflies, damselflies, mayflies, and other insects that these agile birds prey upon in the air. These hardy swallows can also subsist on plant material during cold periods when insects are incapable of flight.
The bodies of Tree Swallows are dark above and pure white below. In mature males the dark upper surfaces have feathers that are iridescent blue, giving them a shimmering appearance in the sun.
By mid-summer most Tree Swallow chicks will have fledged, prompting these birds to begin their long southward migration. They overwinter in the warmer reaches of North America, often living in dense flocks that can be made up of hundreds of thousands of individuals.