The choice of a nesting cavity is important because external factors can negatively affect the productivity of the wren couple. Environmental factors like temperature, temps above 105 or below 65, can destroy the eggs. Nesting parasites can also be a problem, once the chicks hatch, but the clever house wren will often include spider egg sacks when building their nest. When the spiders hatch they eat any parasites that make their way into the nest which helps keep the nestling safe. I photographed this house wren at the Carpenter Nature Center.