A great singer, the house wren is widespread in North America and South America, reaching the tip of Tierra del Fuego in Argentina and Chile. A breeder in the upper two-thirds of North America, the house wren is feisty and aggressive not only to other house wrens but also to other bird species, even those larger than the wren itself. This article is intended to aid in identifying house wren nests and eggs.
House Wren breeding facts
|Breeding Period||Early May through late August.|
|Nest type||A cup surrounded by coarse nesting material. Cup typically sits on a base of sticks.|
|Substrate & Location||Nests are always built inside a natural cavity close to the ground or in nesting boxes.|
|Cavity:||Any type of cavity. House wren also nest in crevices and anything that resembles a cavity, such as hanging boots in a shed.|
|Nesting Activities||The male starts building the nest by first making a base platform made of sticks and then building the nest over it. The female builds the cup and finishes the nest.|
|Egg Description||Pale densely marked with tiny reddish-brown or cinnamon brown dots. Dots are more concentrated on the broad side of the egg.|
|Egg Length and width||0.64 in x 0.5 in.|
|Egg-laying||It begins a day or two after nest completion. Female lays one egg every day.|
|Clutch size||Typically 4-7 eggs. Clutches of 3 eggs or 9 eggs are rare.|
|Number of broods||Two broods per year.|
|Incubation Period||Typically 13 days, ranging between 12-15 days.|
The house wren breeding range encompasses roughly the upper two-thirds of North America from coast to coast. Wrens spend the winter months in the Southern U.S. and move back north to the spring and summer breeding range. The map showing the breeding range indicates the regions where house wren nests and eggs are expected.
The range map (right) shows where the house wren is expected to breed. Source: allaboutbirds.org.
House wren favor semi-open habitats where they forage in bushes, thickets, hedgerows, and the understory of forest edges primarily within 20 feet from the ground. Wrens can be found in rural areas, low-density urban areas, and suburbs with enough vegetation and nesting sites.
Migration and social behavior
The house wren is a short-distance migrant. The breeding grounds encompass roughly the upper two-thirds of North America, which is not far from the wintering grounds in Southern U.S. and Mexico.
House wrens arrive in the breeding grounds beginning in the second week of April through mid-May. After breeding, wrens migrate back to the wintering grounds starting in the second week of September through the first week of November.
Upon arrival to the breeding grounds, males are rather vocal, singing loudly and persistently. Conversely, during the fall migration, birds stop singing, and it is difficult to tell the exact dates when wrens leave the breeding grounds. It is unclear whether house wrens migrate in flocks or individually.
House wren form pairs and defend a territory only during the breeding season. Pairs then split up and return to the wintering grounds, where they have a quiet and solitary life.
Wrens are known to return to the same breeding territories year after year. Although they form new pairs once they arrive in the breeding grounds, some pairs likely meet at the same breeding territory to pair up again for the breeding season.
After pair formation and nest building, females begin to lay eggs as early as the first week of May. By mid-May, most breeding house wren are laying eggs. However, wrens that winter in higher latitudes and higher elevations may start laying eggs later.
The first eggs laid begin to hatch by the last week of May. Young wren may still be seen near their parents as late as the last week of August.
House wren nest appearance
House wrens build round nests with a central cup. Unlike bird nests built by other birds, male house wrens first build a base of sticks that supports the nest. This base of sticks is unique among cavity-nesting birds and can be used as a reference to identify a house wren nest.
Because house wrens are cavity nesters, it is difficult to assess the nest shape.
Hose wrens nest in cavities and enclosures of different shapes and sizes. They adapt their nest to the available space, ensuring that the nest cup and depth are consistently the same sizes. The size and shape that surrounds the nest cup may show a good deal of variation.
House wrens are cavity nesters but cannot excavate their cavities. They use a variety of existing cavities or cavities excavated by woodpeckers.
House wrens can also use crevices at buildings and are creative in finding structures for a nesting site. Wren nests have been found inside hanging boots, flower pots, nestled in tools in sheds, in parts of parked cranes and other machinery, and even in the pockets of clothes hung to dry.
House wren readily take nesting boxes. A study on nesting house wrens found that in areas where natural cavities and nesting boxes were available, house wrens preferred breeding in nesting boxes.
Breeding house wrens typically reuse the same nest when they attempt a second brood. Depending on the state of the old nest, the male may only make repairs and replace nesting material.
Conversely, when the nest, particularly the nest cup, has been heavily utilized and is soiled by the earlier brood, the male proceeds to take most of the nesting material and rebuild a new nest with fresh material.
Ornithologists suggest that replacing the nest material helps clean the nest from parasites that could be detrimental to the next brood.
Male wrens arrive first to the breeding grounds to find a suitable nesting site and territory. The male then proceeds to claim the nesting site by building a platform made of sticks. The male may build more than one nest.
When females arrive at the breeding grounds, they visit territories and inspect nests prepared by the males. If the female approves of the nest, she stays and begins to continue building the nest. This action by the female indicates that the pair have been formed.
House wren are notorious for divorces and mate switching. Most pairs (73%) attempt a second brood in a single breeding season.
For reasons that remain unclear, some females leave their mates and move on to find a new male with a new nest and territory. Males left by females stay in the territory and pair up with available females looking for males.
House wrens have a stereotyped nest-building process. When a male finds a nesting cavity, he first brings sticks into the cavity creating a base or platform.
Potential female mates arrive at the breeding grounds a few days later than the males and inspect nesting sites and territories. If she approves of a nest site and territory, she stays with the male and begins to construct the rest of the nest over the base of sticks built by the male.
The female then builds the cup and lining before beginning laying eggs. The male may assist the female in bringing her food while she is diligently gathering nesting materials.
The house wren eggs are oval-round in shape with an approximate length of 0.64 in and a breath of 0.5 in.
The eggs are pale and thickly spotted with tiny reddish-brown to cinnamon-brown dots, denser in the egg’s broader side. There is little variation among eggs within a clutch.
Overall, house wren eggs may vary across nests. Some have fewer dots and may appear to have less dense markings than others. The color and dotting pattern is similar.
Egg-laying begins soon after the female finishes lining the nest cup. Once the female starts laying eggs, she lays one egg every day in the early morning hours.
The female house wren starts laying eggs as early as the first week of April. The initiation of the egg-laying period varies with latitude, and it is generally later in higher and colder latitudes.
House wrens in North America typically attempt two broods every breeding season. The clutch size for the first brood early in the nesting season ranges between 4 to 7 eggs. Clutches of 3 eggs or 9 eggs are rare.
Clutch sizes for the second brood are smaller on average, ranging between 5 to 6 eggs.
Studies comparing clutch sizes in natural cavities and nesting boxes found that house wrens tend to lay larger clutches in nesting boxes. As indicated above, house wrens chose nesting boxes over natural cavities when both are available.
Incubation of the eggs
Once the female starts laying eggs, she spends some time in the nest and often applies some heat on the eggs. She spends more time in the nest as she lays more eggs.
The female starts incubating the eggs when she still has two to three eggs to complete the clutch. Only the female develops a brood patch and does all the incubation. She takes breaks outside the nest to eat and do other needs. The male delivers food only sporadically during the time the female is incubating.
The female house wren incubates the eggs alone, typically for 13 days. In higher latitudes, higher elevations, and colder temperatures, the incubation period last longer. Overall, the incubation period ranges between 12 to 15 days.
- Brawn, J. D. and R. P. Balda. (1988a). Population biology of cavity nesters in northern Arizona: do nest sites limit breeding densities? Condor 90:61-71.
- Drilling, N. E. and C. F. Thompson. (1988). Natal and breeding dispersal in House Wrens (Troglodytes aedon). Auk 105:480-491.
- Dunn, E. H. (1976c). The relationship between brood size and age of effective homeothermy in nestling House Wrens. Wilson Bulletin 88:478-482.
- Johnson, L. S. and W. A. Searcy. (1996). Female attraction to male song in House Wrens (Troglodytes aedon). Behaviour 133:357-366.