House wrens are cavity nesters. They typically nest in tree cavities but they will also nest in nesting boxes or other man made cavities. They can be quite aggressive in their search for the perfect nest site, often driving away larger birds. The nest is a cup style which is built into a foundation of sticks that the wrens bring into the cavity. The nest cup is lined with feathers, hair, grasses and often spider egg sacks. The later helps to control insect parasites when the spiders hatch. This wren was nesting at the Carpenter Nature Center.