House Wrens (Troglodytes aedon) are one of the most-studied birds in the USA. One of the primary reasons why this is the case is because House wrens often nest in close proximity to humans and human settlements.
This is your complete guide to House wren nesting, where we'll go into the nesting behaviors, appearance, construction and much more!
House wrens are cavity nesters and will nest in virtually any small cavity ranging from a coat pocket to an old woodpecker nest. The cavity only needs to be around 10cm x 10cm x 10cm in size - these are exceptionally small birds.
These crafty cavity nesters choose some weird and wacky locations, like the interior of skulls or craniums hanging outside people’s houses, coat pockets, tin cans, and abandoned machinery. Despite their nests being so small, they’re intricate and are built from hundreds of small sticks.
Of course, there’s much more to learn about the nests of these small and beautiful birds - read on to learn more!
House Wrens are cavity nesters, and nest in an array of places
House wrens nest across virtually every US state, southern and mid-Canada, and more or less the entirety of Central and South America. They have one of the widest ranges of any songbird in the Americas. Habitats vary, ranging from various lowland and upland forests and woodlands to parks and human settlements.
Nests are chosen in a huge variety of small cavities, but House wrens prefer pre-formed cavities in trees. Some cavities are natural, e.g., in a dying, damaged, or diseased tree, whereas others are the remnants of other cavity-nesting birds, such as kingfishers, American robins, swallows, and woodpeckers. They don’t seem to have a preference for tree species.
Artificial nesting sites range from cavities in rotting or decaying structures to novel choices like coat pockets, tin cans, ornaments, abandoned vehicles, and machinery. In addition, nests have been found in boots, shoes, and a multitude of other small artificial cavities.
Most nesting sites are built close to the ground, but some have been found at the height of 30ft or so. House wrens prefer to stay within 30m or so of woodland or forests. However, relatively open sites are preferred over those within dense foliage or tree cover.
Many cavities are reused each year. When reusing nests, the male typically excavates the cavity and removes most sticks. This is thought to reduce parasitic mite infestations and other insects that have taken residence among the nesting materials.
House Wrens nest in many different cavities, including holes in buildings, and even coat pockets!
House wrens certainly nest in backyards if there are valid nesting cavities, either natural or artificial.
These small birds are easily supported with nesting boxes, so long as they’re small enough to prevent use by larger songbirds. A House wren nesting box can be as small as 10 x 10 x 10cm with a 2.5cm entrance/exit hole.
Do House Wrens use nest boxes?
House wrens are not especially picky about what cavity they nest in, so long as it’s small with a small entrance/exit. Nesting boxes suitable for House wrens can have a base as small as 4 x 5in.
If the box is too large, other birds will nest inside and might kick wrens out or even attack or eat their nestlings.
Any trees with valid cavities suit House wrens. Studies show that they have no real preference for tree species, so long as it’s around 30m or so from vegetation, presumably as this enables access to food and nesting materials.
With that said, most wrens avoid heavily vegetated areas and avoid dense vegetation unless there’s no alternative - probably because clear nesting sites make it easier to spot incoming predators.
House wrens typically nest low to the ground, at the height of just 3 to 5ft or so. However, in some cases, they nest in the first story of a large tree at the height of 30ft.
House Wrens will use nest boxes in backyards
Once he selects a nesting site in a territory, the male begins to line it with twigs. Sometimes, males will comprehensively line the nest with hundreds of sticks, but other times, they’ll add just a handful.
Interestingly, males add other items such as wool, cotton, and the cocoons or egg sacs of spiders and other arthropods. It’s thought that hatching spiderlings consume mites and other parasitic insects, thus cleaning the nest.
The finished nest is built within the cavity with a platform around 4 to 10cm high. The platform is then molded into a slight indentation.
House wren nests are small, measuring as little as 10 x 10 x 10cm, with an internal volume of 1000cm2. That’s about the size of a large tin can. Larger nests double that size have been reported, but some are smaller, measuring just 800cm2 or so.
House Wren nest inside of a nest box
At the start of early spring, unpaired males begin scouting nesting sites to form basic nests. This occurs as early as late February in some US states. Nests are built from March to May when unpaired birds pair up and refine their chosen nest.
First eggs are laid as early April in warmer parts of the US and Mexico or as late as May at northern latitudes. Second broods are raised between June and July.
When House wrens breed further north, they begin selecting nesting sites as soon as they return from migration in late winter or early spring.
Some nests are constructed as early as late February. Many wrens usually raise two broods, which takes them all the way through to July and August. Wrens have a long breeding season compared to many birds.
First eggs are typically laid no earlier than April. However, Wrens are more likely to breed earlier at southern latitudes where it’s milder in late winter and early spring.
Further north, the first eggs are usually laid in May. Studies in Wyoming, New York, and Ohio indicate first eggs are laid in mid-May, whereas in southern California, some eggs appear in April in warm lowland areas.
Further south in Central and South America, House wrens remain in their breeding territories throughout much of the year. Further north in the US and Canada, House wrens migrate each year and roost in warmer regions.
House Wren chick almost ready to fledge from the nest
At the start of the breeding season, the male House wren seeks out eligible nesting cavities and begins preparing them for nesting. First, he lines the nests with sticks, sometimes comprehensively with hundreds of sticks, other times with just a handful of sticks.
After the male finds a mate, the female takes over building duties and finishes the nest. Nests typically feature hundreds of small sticks (around 300 to 500 or so in some studies).
Twigs form a platform that elevates the base of the nest from the bottom of the cavity, aiding in drainage and insulation.
House wrens use various nesting materials but most commonly choose small, soft twigs. Artificial items such as wool, cotton, rope, and plastic are added to the nest by the male.
The male also adds spider cocoons and egg sacs - researchers think this might be a deliberate choice to help clear the nest of mites.
Once the spiderlings hatch from the cocoon, they essentially clear the nest out of harmful mites and other parasites, as the spiderlings themselves pose no real danger.
The male starts the nest and finishes it to varying degrees of completeness. In some cases, he might add hundreds of sticks to the nest, and in others, he might add just ten or so sticks to the nest.
Once the male pairs with a female and they decide on a nest to finalize, the female typically takes care of finishing it off and putting the final touches in place prior to laying eggs.
The female House Wren might make 200 to 300 trips back and forth from the nest in this time in a process that can take as long as 14 days.
House Wren gathering nesting materials
House wren eggs are tiny, measuring just 1.6cm long and weighing just over 1 gram. They’re a brownish color with heavy red-brown spots and blotches, which are sometimes purplish. Pigmentation is concentrated towards the larger end of the egg. Rarely, eggs lack any pigmentation.
House wrens lay around 5 to 8 eggs, sometimes more. However, on rare occasions, over 10 eggs have been observed up to a maximum of 16!
Males don’t incubate, but they do remain attentive to the female and the nest during the incubation period. The male occasionally visits the nest to feed the female.
Two House Wren eggs next to a Cowbird egg
Most studies show that House wrens leave the nest after around 14 to 15 days, give or take a day or two.
Most pairs of House wrens attempt to raise two broods. The second brood is raised in a separate nest after the nestlings have fledged. The male may continue to feed the young birds as the female prepares the next nest.
Both the male and female feed the nestlings. Parents make a combined 20 to 30 trips to and from the nest each hour.
Adult House Wren attending to their hungry chicks
House wrens rarely abandon their nests and will only risk doing so if the nest is under indefensible threat or otherwise fails, e.g., due to insect infestation or flooding.
House wrens don’t typically nest on the ground but do nest very close to the ground or inside items resting on the ground. They typically nest at the height of 3 to 5ft.
Like most birds, House wrens roost in trees at night. The exception is the breeding season, when the female sleeps in the nest while incubating eggs or brooding the nestlings.
House wrens are easy to support with nesting boxes, provided the box is small with a small entrance that deters other birds. The hole can be as small as 1 ¼ or 1 ⅛ inches large.
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