Bluebird and Small Cavity Nester Conservation
Sialis - Bluebirds and other small cavity nesters
 
bluebirds

eggsAll About House Wrens

Contents: Species, Identification, Distribution, Diet, Nesting Behavior, Nestboxes, Nestbox Location, Monitoring, Nesting Timetable, More Info and Photos of Nests, Eggs and Young. Also see Deterring House Wrens and Video Clip of House Wren Attacking Eggs, and Other Brown Birds.

House wren - male? Photo by E Zimmerman

NOTE: my primary interest in House Wrens is deterring them from using nestboxes. While they are native birds, eat lots of insects and have a cheery song, they are aggressively territorial and prolific, and I choose not to encourage them to use nestboxes on my trail, especially since their populations are already on the increase. Some folks love them.

Species: There are about 31 subspecies (previously treated as separate species) of the House Wren, or HOWR, divided into 5 different groups. This web page deals with the Northern House Wren (Troglodytes aedon - called Sylvia domestica prior to 1809). The Chippewa Indians called it O-du-na-mis-sug-ud-da-we-shi, meaning big noise for its size. Sometimes referred to as a "Jenny Wren." Also see Carolina Wren, and less common Bewick's Wren.

Identification: This little brown bird has a long pointy, curved beak and up-cocked tail. Their short (stubby), round wings enable them to maneuver through dense vegetation. Sexes are hard to tell apart. It sports dusky brown "eyebrows" versus the distinctive white eyebrow-stripe of the bigger Carolina Wren (Thryothorus ludovianus). Juvenile House Wrens have a reddish brown rump, and their underparts are a darker buff. The Carolina Wren has a warm brown breast. The Winter Wren (Troglodytes troglodytes) is smaller, and darker, with a shorter tail that is more cocked upward. It is also more likely to bob its head and has distinctive tip-tip call. They are energetic and zippy, with pinkish legs and fairly large feet. The Bewick's Wren (Thryomanes bewickii) is more slender, rather long necked, with a very long, barred tail. Their beak is longer and straighter than a House Wren. It also has a long white stripe over its eye, and its breast is white. Cactus Wrens are really big and look almost like thrashers. There are also Sedge, Marsh, Rock and Canyon Wrens.

WREN SPECIES RELATIVE TO THE HOUSE WREN

WREN Eyebrow Beak Tail Breast Legs Color Size Habitat
Bewick's Very bold Longer, straighter, slender Long w/ gray & black bars & white spots, often cocked upward White, grayer underparts Dull pale brown No buff or orange on underparts Smaller, More slender than Carolina  
Carolina Bold, cold white Pointed, slightly decurved No white spots Warm brown   Buffy underparts Stocky, large head  
House Faint, plain face Shorter than Bewick's Shorter than Bewick's, no white spots Dingy, gray throat Pinkish More uniform brown, Wings heavily marked, grey brown underparts Smaller, more slender than Carolina  
Marsh                
Rock     Buffy tail corners Whiter w/ buffy flanks   Paler gray-brown above   Dry west
Sedge               Marshy reeds/grasses
Winter Fairly bold   Shorter, more often cocked upward Stronger barring on belly and flanks   Darker   Marshy reeds/grasses

Interesting Facts:

  • Males may belt out their effervescent trill 3-11 times per minute. When they first arrive in the spring (About 9 days before the females) they may be silent.
  • Males and females have high nest site fidelity (returning to the same or nearby territory each year.)
  • Both males and females may quiver their wings during mating, or when disturbed or scolding.
  • An experienced female can maneuver 4 or 5 sticks into the nestbox in the course of one minute during nest building.
  • In the course of 4.5 hours, a female wren made 110 visits to feed her nestlings. (Judd 1900.) 98% of their diet is insects - mostly bugs (like stinkbugs), grasshoppers, caterpillars and beetles. (Beal 1897.)
  • The House Wren song may be considered loud and clear or shrill and grating. The Chippewa Indians, called it O-du-na-mis-sug-ud-da-we-shi, meaning big noise for its size (Cooke 1884).
  • House wrens occupy the broadest latitudinal range of any native passerine in the New World (BNA.org)
  • Females pick their mate, mainly based on the quality of a nest site. (BNL.org)
  • A usurping male almost always removes existing eggs or young, but the resident female stays with the usurper about half the time (Kermott et al 1991)
  • Parents usually remove damaged eggs and dead nestlings (even almost fully grown.) (BNA.org)
  • The House Wren species name is after Aëdon, Queen of Thebes, who accidentally committed infanticide while trying to kill a rival's son.

Song: Chattering, vibrant, energetic. Both sexes sing (males 3-11 times per minute!). Loud singing bouts of 4-10 minutes might indicate an unmated male. They do continue to sing when mated. "The persistent repetition of its nervous energetic outbursts has after a time a tendency to tire the listener." (Gross, 1948) HOWR males do make a "Whisper Song" (without opening their bill) while copulating.

Nine day old House Wren chicks. Photo by LC Moore.Distribution: Ubiquitous in fragmented forest (edges, small woodlots), swamps, farmland, residential areas and parks near trees and shrubs. Breeds from across most of Canada down to the southernmost part of South America, and into the West Indies. See map. Generally not found in the desert, or in high elevations in mountains. Birds nesting in the southern US (e.g., Alabama) MAY be non-migratory, but most HOWRs migrate to southern U.S. or n. and central Mexico for the winter, arriving north in mid-March through mid-May, depending on the location. Older, more experienced birds tend to arrive earlier. (Are some southern HOWR non-migratory? Do they migrate in flocks or alone?)

Supposedly 90% of males stay within a 1.25 mile radius during nesting season (Fitzwater fact sheet reference)

Most northern individuals leave breeding areas from September-early November.

Diet: 98% animal matter - generally less mobile critters like bugs (stinkbugs, leaf hoppers, etc.- 29.34% of diet), grasshoppers, crickets, caterpillars and beetles, spiders, ants, bees, wasps and flies. They do eat pests such as gypsy moths and cabbage worms (moths and caterpillars make up about 13.9% of their diet), locusts and ticks. Beneficial insects make up only about 3% of their diet.(Beal 1897.) Beal found no evidence that they eat fruit or farm products.

Nesting Behavior: House Wrens arrive in nesting territory from late March to mid-April or early May, depending on the latitude. They typically begin nesting, on average around May 11 (May 1-June 22 per Keneigh, 1941)

The female chooses the nest site, and may rearrange or completely remove a dummy nest placed by the male. Both the female and male construct the nest, but the male focuses on singing and guarding the nesting territory.

An unmated male does not sleep in nest cavity, but females may do so on most or all nights during nest-building until young fledge. Nobody knows exactly how much territory a male HOWR will defend, although some have speculated about one acre. Usually active nests are almost 100 to 230 feet apart.

HOWRs are very territorial within their species and with other species, and may peck and remove eggs and young from nests. Predation may be highest in areas where HOWR populations are highest. More nestboxes = more HOWR = more predation.

Polygynous. Pairs don't usually stay together after the end of the breeding season (only reuniting less than 4% of the time in one study), and they commonly switch mates for subsequent broods in the same year. Sometimes one male will serve two females, picking up the second while the first is "busy with household duties." (Bent)

A mateless male House Wren fed nestling House Sparrows (Hills 1924. It is rare to find other species feeding House Sparrows - Shy found only 2 records.)

Nestboxes: House Wrens are secondary cavity nesters, meaning they cannot excavate their own nesting holes. Tolerant of human activities. HOWR may prefer a box with a smaller floor space. A typical nestbox recommended for HOWR has a 4 x 4", is 6-8" deep, hole 4-7" above the floor, 1-1.5" hole, mounted 6-10 feet off the ground. Nests naturally in existing tree cavities, especially old woodpecker holes, but readily uses nestboxes. Also nests in variety of other crevices or cavities—e.g., in a flower pot, tin can on a garbage heap, boot, scarecrow, pocket of hanging laundry, paper hornet nest (excavated first). Also in a hole in a brick wall; deserted barn swallow, Baltimore House Wrens eggs. Notice gloss.  One in upper left corner is smaller than others. Photo by E Zimmerman.Oriole, osprey (in the deep interstices), robin, or phoebe nest, and even in a kingfisher's nest hole in a sand bank (Bent); mailbox, farm machinery, soap dish, or cow skulls hung on walls. One pair of wrens built their nest on the rear axle of a car that was used daily. When the car was driven the wrens went along, and eggs actually hatched. (Northcutt, 1937).

In one study, when HOWR were given a choice of red, yellow, blue, white and green nesting boxes, they preferred red and green, and used white the least. (McCabe, 1960.)

Nestbox Location: HOWR may prefer cavities closer to ground (10.5-17.7 feet, up to 30 feet) and with smaller entrances (1.6-2.2 inches) than other cavity nesters in local area, and show no apparent preference for cavities that open in particular directions, for cavities in snags versus living trees, or for cavities in particular tree species. At one California site, they preferred nest sites that were farther above ground with a smaller floor area, and tended to open more southeasterly than northerly.

Prefers sites near deciduous vegetation/edge, especially if there are lots of snags (standing dead trees). Usually avoids nest sites ≥100 feet from any significant woody vegetation, unless there are no other options. However, also avoids sites in heavily vegetated locations where visibility is low. They do prefer sites where the nest is concealed on all sides except the point of entrance.

House Wren habitat often overlaps with chickadee and titmouse habitat, resulting in competition which House Wrens typically win. I wonder if forest fragmentation is resulting in increased HOWR populations.

Rarely nests in rock crevices, holes in sandbanks (Winnett-Murray 1986) or open cup nests (e.g., of Eastern Phoebes or Barn Swallows.)

Spacing: Active nests for different males are usually separated by more than about 100 feet (Muller et al 1997), but sometimes by only 33 to 50 feet. (DeMory et al 2010).

Monitoring: Generally quite tolerant of occasional disturbances at nests. After eggs hatch, adults may (rarely) attack a monitor (watch out for your eyes!). Female may desert nest if trapped in nest before midpoint of incubation stage, but usually does not desert later. Young are likely to fledge prematurely if disturbed late in the nesting cycle.

At fledging, nests may contain >50,000 mites (ugh). Egg sacs of predatory jumping spiders are often stuccoed to the sticks used in nests, and the baby spiders eat the mites (in the lab at least - in the field, they didn't reduce the number of mites in actual nests.) Some researchers think spider/moth egg sacs are only added/chosen for decoration. (The presence of cocoons had no effect on number, mass or condition of babies. (Eckerle and Thompson 2005)

One researcher developed psittacosis apparently after contracting the bacterium Chlamydia psittaci from a nest in Minnesota (probably after breathing dust-borne, dried fecal matter.)

Nesting Timetable (typical): Breeding generally occurs from March/April through August in the U.S. Nest building to fledging takes about 36 days (35 to 45.) Compare this to the Bewick's Wren, which takes 52 to 53 days from start to finish.

  • Arrival: breeding season begins in late April for birds living in south; early May in the north. Breeding is later at higher latitudes and altitudes. Male arrives first, establishing territory with crude dummy nests. Male begins constructing nests in empty cavities within a few days if not hours of arriving back from migration. Female selects actual nesting site.
  • Excavation: HOWR do not excavate their own holes.
  • Nest construction: Breeding usually starts around mid-May through the end of June for the first brood, late June through the middle of August for the second brood.
    • The male generally removes old nesting material from a site (but often re-uses the same sticks.) The male puts sticks in nest site(s), and then the female selects the cavity where she will lay her eggs.
    • Dummy nests: HOWR males often build loose dummy nests in other nearby cavities, of <10 to >400 sticks. If sticks are removed repeatedly, and the pair intends to actually use the nest site, the nest may eventually consist of a typical nest cup material only.
    • Once the female has selected a site, she starts over (but may reuse sticks from the "dummy nest" made by the male.) Nests are finished rapidly in (2-3 per Bent) 3-14 days by the female. See nest and egg ID information. Hundreds of small dry, coarse sticks are placed in bottom of cavity to form a tall base 4-6" deep. One nest in Iowa was made up of "52 hairpins, 68 nails (large), 120 small nails, 4 tacks, 13 staples,10 pins, 4 pieces of pencil lead, 11 safety pins, 6 paper fasteners, 52 wires, 1 buckle, 2 hooks, 3 garter fasteners, and 2 odds and ends." The narrow nest cup is eventually lined with grass, inner bark, hair, rootlets, and finally feathers. It may be located in the rear of the cavity for protection from predators. Total trips to nests/day for female before egg-laying may exceed 300 (average about 170). Late in season, female may begin laying eggs before cup lining is complete. In some cavities, birds have to crawl up and over mound of sticks to reach nest cups deep in rear of cavity, which probably protects egg and young from predation.
  • Egg laying: 1 egg per day, laid very early in the morning, with a typical clutch having 5-8 eggs (usually 5 or 6). Three and 9-10 egg clutches are rare - up to 12 reported.
    • Egg ID: Tiny, shiny, short-rounded ovate to oval. Base color is white, densely speckled with minute dots of brownish-red or cinnamon brown, making the egg look overall salmon or reddish-brown colored. The color is deepest on the rounded end, and the egg may have a wreath of spots concentrated there. Eggs measure on average 0.64 x 0.50 inches (length 0.58 to 0.70 inches, width 0.46 to 0.53 inches.)
  • Incubation: by female only, for 12–13 days, depending on the temperature - the period shortens later in the season. The eggs are kept at a temperature of about 35 C. Maybe up to 15 days after the penultimate (next-to-last) egg is laid. The hotter it is, the less time the female spends on the eggs. The female may actually apply some heat to even the first egg that is laid, but does not start full incubation through the night until laying the ante-penultimate or penultimate egg.
  • Hatching: Since incubation begins on the ante/penultimate egg, hatching may be asynchronous in about 1/4 of nestings, over a 1-2 day period. Babies are fully altricial (practically naked). Eyes are closed.
  • Development: Both parents feed babies. At day 3, parents may begin feeding grit and bits of shell. The ability to thermoregulate depends on the number of siblings in the nest, ranging from 4 days to 9 (more siblings = more insulation = earlier themoregulation.) Brooding (by the female only) stops in the latter 1/3 of the nestling stage (babies can thermoregulate around day 7 or 8). Feathers emerge during week 2. Whole broods of healthy young can die of apparent hypothermia in poorly ventilated, unshaded nestboxes when temperatures exceed about 90 °F. Parents often remove both damaged eggs and dead nestlings (even nestlings almost full-size) from the nest. Parents eat or later remove fecal sacs. Nests may contain blow flies (Protocalliphora sp.) (Note: If the female is lost/deserts, the male may be able to rear them successfully if they are a week or older.) The young consume enormous quantities of food as they get older. In the first few days of hatching, the babies "peep," which turns into a harsher sound over the next week.
  • Fledging: 12 to 18 days, usually 16-18 days. The earliest “normal” fledging could be 24 days, up to 33 days after next to last egg is laid. May occur over 1-4 days. Very small runts can be left behind to die in the nest. Young are fully independent about 12-13 days after fledging. Female may re-nest at this point. Prone to premature fledging if box is opened late in the cycle. It is difficult to visually sex juveniles, as they all look like females, until the black bib and chestnut colored feathers on the wings start to develop several weeks after fledging. They will breed the following year, at the age of 1 year.
  • Number of broods: Usually 2, sometimes 3 broods per season. (3 broods are rare and the third may not be successful.) One brood at high altitudes or latitudes. For second brood, production may begin 50–60 days after first egg of season is laid. If the previous nest is not removed, the wren will renovate it with a thin layer of nest material plus a new nest lining, often within a day or two after fledging.
  • Nest Site Fidelity: Maybe 1/4 to 1/3 of males may return to the same breeding territory each year, but results of different studies differ. (Kendeigh reported 75% return in 1941.) Females with failed nestings in the last attempt of the previous season moved farther away than successful females (same not true of males).
  • Longevity: 7 years and 1 month recorded (Valentine 1971). Fitzwater says an individual lived in captivity for 23 years, however no reference is provided.

References and More Information:


One cannot watch a pair of wrens in their repeated attempts to get long unwieldy sticks through a narrow box entrance scarcely large enough to admit their tiny bodies without being greatly impressed by their dogged persistence, energy, and skill.
- Alfred Otto Gross, Life Histories of Familiar North American Birds, 1948


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