Wrens are small, highly energetic songbirds recognized by their loud vocalizations and the habit of holding their tails upright. These birds, particularly the widespread House Wren, are classified as secondary cavity nesters, meaning they rely on existing enclosed spaces for shelter and reproduction rather than excavating their own holes. The selection of a nest site is a deliberate process focused on protection from predators and the elements, leading to remarkable adaptability in their choice of location.
Natural Cavities and Concealment
In undeveloped landscapes, wrens depend on natural features that provide the necessary small, dark, and enclosed space for nesting. These locations often include abandoned woodpecker cavities, naturally occurring hollows in old trees, broken limbs, tree stumps, and crevices found in rock faces or stone walls.
Wrens prefer habitats such as forest edges, thickets, and areas with dense, shrubby undergrowth. Their small size allows them to use cavities that larger, competing birds cannot access, reducing competition for resources. They rarely select a nest site more than 100 feet away from surrounding woody vegetation, reflecting their reliance on nearby cover.
Adoption of Man-Made Structures
Wrens exhibit a high degree of opportunism near human habitation, readily adopting structures that mimic natural cavities. Birdhouses are a popular choice, but wrens prefer nest boxes featuring a small entrance hole, typically between 1 and 1-1/8 inches in diameter. This restricted opening size helps exclude larger, more aggressive cavity-nesting competitors.
Their site selection is famously eclectic, extending to a wide range of man-made objects found in yards, garages, and porches. They explore the nooks and crannies of buildings, sometimes nesting in crevices in eaves, vent openings, or the clutter of machinery in a shed. Unconventional nesting spots include:
- The interiors of mailboxes
- Hanging flower baskets
- Discarded tins
- Old boots or shoes left outdoors
Nest Architecture and Materials
Nest construction begins with the male, who fills the chosen cavity with a substantial foundation of small twigs and sticks, often filling the entire space. The male may start multiple such “dummy” nests in different locations within his territory, which signals his vigor to a potential mate and deters other birds.
Once the female selects one of the male’s stick foundations, she takes over the final stage of construction. She creates a soft, cup-shaped depression within the top of the twig base to hold the eggs. This inner cup is lined with fine, softer materials collected from the immediate environment, such as grass, moss, animal hair, and feathers.