|Adult sitting on a cholla cactus in the White Tank Mountains, Arizona|
|Distribution map of the cactus wren.|
The cactus wren (Campylorhynchus brunneicapillus) is a species of wren that is endemic to parts of the southwestern United States, as well as northern and central Mexico. There are eight recognized subspecies, and the nominate species has a brown crown, with notable white eyebrows that stretch to the nape of the neck. Its wings and feathers are brown, but are marked with black and white spots. The tail, as well as certain flight feathers, are also alternatively barred in black and white. The chest is whiter, while the underparts are cinnamon-buff colored. Its song is harsh and raspy and has been described like a car engine that will not start.
They are well-adapted to their native desert environment, and can fulfill almost all of their water needs from their diet, which consists of mainly insects supplemented with some plant matter. They are ground feeders – but somewhat poor fliers – which leads to much of their time spent either hopping on the ground for food, or sitting on perches calling.
This wren's common name comes from its frequent use of saguaro and cholla cactus as nesting sites, which provide protection to both young and roosting adults. Their football-shaped nests are constructed first of plant material, then lined with feathers. Cactus wrens are non-migratory, and carve out and defend territories around their nests. Pairs are monogamous, with females incubating eggs while males build additional nests; both parents feed chicks.
Populations have been in decline as the species faces threats related to human activities and habitat loss. Habitat fragmentation and fire have been of particular concern, as the cactus wren is slow to disperse into new habitat. Introduced species, such as exotic grasses and domestic cats have also hurt populations. Despite these threats, the cactus wren has proved adaptable and its population numbers in the millions – leading the International Union for Conservation of Nature to consider the cactus wren as a species of least concern.
Taxonomy and systematics
The wren family is a group of generally small passerine birds, found – with one exception – only in the New World. Although the cactus wren represents the largest wren in the US, it is not in fact the largest wren: that title is shared between the giant wren and the bicolored wren. It is sometimes considered conspecific with the Yucatan wren and Boucard's wren, but there are numerous morphological and behavioral differences between the species. Conspecificity is not supported by genetic study with either species. Work on wren taxonomy in the 20th century postulated that the Yucatan, Boucard's, and cactus wrens – along with the spotted wren – might constitute a superspecies. More recent study however showed this to be unlikely, as the cactus wren was shown to be ancestral to the other species. Evolutionary study of the cactus wren suggests that it evolved in central Mexico, and that the wren then quickly spread to its modern range.
Various subspecies of the cactus wren have been described, and 8 are generally recognized. However, DNA research has shown that there may be only 2 lineages within the species. The exact taxonomy of the cactus wren remains under debate, and not all subspecies are universally recognized.
- C. b. couesi Sharpe, 1882 – Covering most of the cactus wren's range in the southern United States, including Nevada, Utah, Arizona, New Mexico, and Texas, as well as Sonora and Chihuahua states in Mexico. The American Ornithologists Union classifies all California subspecies as C. b. couesi. It is larger than the nominate race and has paler underparts. Sometimes referred to as C. b. anthonyi, but couesi takes precedence.
- C. b. sandiegensis Rea, 1986 – Found in Baja California and parts of southern California. This species is not accepted by the American Ornithologists union, who instead believes it to be an intermediate between C. b. couesi and C. b. bryanti, and classifies it as the former. Crown lacks or has lessened red tinge on crown compared to nominate race. Eggs darker than other races.
- C. b. bryanti (Anthony, 1894) – Found along the western coast of Baja California, it is separated from the range of C. b. couesi by at least 150 miles. Has notable white markings on the rump and scapulars. Upperparts are darker and more brown than the nominate race.
- C. b. purus (van Rossem, 1930) – Present on the eastern and western coasts of Baja California. Its underparts are almost pure white, and its flanks are notably less cinnamon colored than the nominate race.
- C. b. seri (van Rossem, 1932) – Found in the Gulf of California. Underparts are less cinnamon than nominate, and the spots on its abdomen are wider. Although officially recognized as a subspecies, molecular DNA studies have shown that seri may not be a distinctive race.
- C. b. affinis Xántus, 1860 – Found in southern Baja. Underparts paler and less black marks than nominate race. Rectrices, excluding the middle pair, have white bars. Tends to lay less eggs than other races, generally 2 at a time instead of 3-5, and those eggs are notably paler than that of other races. This race is sometimes further broken into affinis and purus, but this distinction is not widely recognized.
- C. b. brunneicapillus (Lafresnaye, 1835) – Range is in northern Mexico in Sonora and Sinaloa state. Brunneicapillus is the oldest classification of cactus wren, and thus includes members of C. b. couesi. Its flanks are more buff colored and the spots on its abdomen are more delineated than the nominate race. Its distinction from other races is enhanced by its pure white chin.
- C. b. guttatus (Gould, 1837) – Found in central and southern Mexico. It is duller and more grey than the nominate race; its upper parts have less noticeable white markings.
The cactus wren is the largest wren in the United States and has a thick, heavy bill that is dull black, and slightly curved downwards. The bill is about the same length as the head.:1 The tail is long and rounded. This wren is between 18 centimetres (7.1 in) and 19 centimetres (7.5 in) long, and weighs in at between 33.4 grams (1.18 oz) and 46.9 grams (1.65 oz).
The coloration of the nominate race is brown with white speckles, and has distinctive white eyebrows that run from the bill to the nape of its neck. The nape is brown, with additional white markings. The chin is white, while the neck has black markings on a mostly white background. The lower mandible is grayish and pale. The rump and back are grey to brown with white and black streaks. The chest is white with brown or black speckles. Its belly is generally white, with some brown or black streaks. Both the lower underparts and flank are cinnamon-buff colored. The crown is chocolate-brown with a light red tinge.
The supercilium (stripe above the eye) is white. The cactus wren's 10 primary and 9 secondary feathers are barred, alternating between black and off-white. Its 12 rectrices (tail flight feathers) are barred, alternating between brownish-black and pale grey-brown. Outer rectrices are white tipped. The tail is barred in alternating stripes of black, white, and brown. Legs are brown to pink-brown.
Males and females look alike; juveniles can be distinguished by their paler coloration and red-brown to muddy-grey eyes. Adults have more red-brown to red eyes. Additional juvenile differences include the lack of a white nape streak, and less noticeable black chest markings. Summer often takes a harsh toll on plumage; the intense desert sun and prickly vegetation fade and damage feathers. This wear and tear can make identification of juveniles more difficult. Worn feathers are replaced by moulting, which happens in adults July through October – usually on the bird's own territory – but not all feathers will be moulted in a season.
The cactus wren is not easily mistaken for other species. A notable difference that can assist in identification is the white tail band seen in flight. Although it looks similar to other wrens in the genus Campylorhynchus, their identification is eased in that their habitat does not overlap. The spotted wren looks similar, but is paler and has less markings, and its habitat is in oak woodlands (where cactus wrens do not usually live).
Its main call is a harsh and raspy series of “jar-jar-jar”, or "char" notes, which increase in volume and pitch as the song goes on. Each part of the call lasts around 4 seconds, with 4–8 seconds between calls; calls can carry up to 1,000 feet. It has been described as sounding "like a car that just won’t start". Males are the primary singers, although females can sing too – their song is weaker and higher pitched. Males begin singing before dawn and prefer to vocalize from high vantage points, such as trees, telephone polls, tall cacti, or roofs. At least 8 other songs exist besides the main call. A "buzz" or "tek" are given as warning calls. "Growls" serve as a mating and identification call. "Rack" calls are used for locating an existing mate, or other wrens – this call is often the first vocalization made upon leaving the nest. A high pitched "squeal" is given only during nest building, and is heard very rarely. "Scri" notes are let out during territorial disputes with other wrens. Chicks make various begging vocalizations, including a soft "peep". Fledglings, and only fledglings, are known to make a "dzip" call. Calls are made while the break is held just slightly above horizontal.:32
Distribution and habitat
The cactus wren is a bird of arid and semi-desert regions. Its range includes the Sonoran and Chihuahuan Deserts, and generally requires spiny cactus to nest in. The cactus wren is not migratory, and carves out permanent territories which it defends vigorously. Territories average 1.3 hectares (0.013 km2) to 1.9 hectares (0.019 km2). The size and shape of territories change very little throughout the season.:18 Territory is defended from other birds by fluffing tails and feathers and vocal scolding. Persistent trespassers may cause the wrens to give chase.
The cactus wren's range is bi-national, existing in only the United States and Mexico. In the U.S. it is present in California, Nevada, Utah, Arizona, New Mexico, and Texas. In California it is found mainly as southern coastal populations existing below 600 metres (2,000 ft), but some have been found up to 950 metres (3,120 ft). California populations have become increasingly fragmented due to habitat destruction. Nevada represents the northernmost portion of their range, they exist in the southern tip of the state, the most northern breeding population is found in Nye County, near Tonopah. They are found only in the smallest portion of southwestern Utah. Their range in Arizona is widespread throughout the southern part of the state, and along the Colorado river. In Arizona it is found from sea-level up to 1,400 metres (4,600 ft). Populations in New Mexico exist in the south, down to along the Rio Grande and into Mexico. Their range in both New Mexico and Texas may be expanding northward. Texas cactus wrens live between sea-level and 1,800 metres (5,900 ft), throughout the Texas panhandle, central Texas, and as far east as Travis County. In Mexico it is found in Sinaloa, Sonora, Chihuahua, Coahuila, Neuvo Leon, Hidalgo, and throughout Baja California. On the Central Mexican plateau and in New Mexico it is found up to 2,000 metres (6,600 ft). Populations may be expanding their range in Baja California, but they are not found in the mountains or interior of Baja.
Behaviour and ecology
The cactus wren forms permanent pair bonds, and the pairs defend a territory where they live permanently and year-round. There is a distinctive greeting call between pair members, where they spread their wings and tails and give a harsh call. The same motions are used as a breeding display, but with a non-ritualized duet call. Since males and females are identical, birds recognize members of the opposite sex not by size or color but by behavioral differences. Males are more aggressive and are more frequent singers.:34 Mating displays begin with a growl-like noise, and end in gentle pecking. Displays are incredibly short, lasting only 2–3 seconds.:35 Mating happens beginning in late February and runs through March. Egg laying begins around the same time, but is delayed at higher elevations. Good monsoon conditions can extend breeding: young have been recorded in nests as late as August.
Nests are built in cacti (notably cholla, prickly pear, and saguaro), thorny desert trees, or yucca. Where available, jumping cholla is overwhelmingly preferred.:22 Nests average about 3 feet (0.91 m) off the ground, and are usually less than 10 feet (3.0 m) off the ground, but have been recorded as high as 30 feet (9.1 m). Nests are the size and shape of an American football and are constructed of grass, twigs, feathers, weeds and other light detritus. The nest is lined with feathers and down, which may come from cactus wrens or other species. Nests built in urban settings use a much wider variety of materials, including many human made items such as paper, string, lint, and notably: chicken feathers.:24 Urban materials, while easily available, make for weaker and less sturdy nests.:28 A tube like entrance, about 15 centimetres (5.9 in) long, leads to the main nest cavity. The entrance is often oriented to take advantage of the cooling effects of prevailing winds. Nest building takes between 1 and 6 days, with Anderson and Anderson reporting an average time of 2.7 days.:26 The nesting pair generally focuses on nest building only in the first 3 hours of every morning.
Multiple nests are often built. The first nest of a season may use an existing nest that has been renovated, although subsequent nests will usually be made from scratch. Adult roosting nests are usually separate from breeding nests, and are less sturdily constructed. While the female lays one clutch, the male will start to build a second nest. As soon as the first brood fledges the female will assist in additional nest building. Once completed a new brood will be laid. As many as 3 broods may be raised in a single year, although 1 to 2 are more typical. Up to 6 broods may be attempted in a year, but rarely more than 2 or 3 will survive.
Cactus wrens lay 3–4 (as many as 7 have been recorded) white to pale pink eggs covered in brown speckles, which are smooth and ovate. Eggs are 23.5 mm × 17 mm and average 3.57 grams (0.126 oz) in weight. Egg laying begins about a week after nest completion, and is done one egg per day in the morning. Incubation takes about 16 days and is done solely by females. Wrens are known to destroy the eggs and nests of other nearby birds, but do not engage in, nor suffer from, brood parasitism.
A far more serious issue facing cactus wrens is the Curve-billed thrasher. Both birds have roughly the same range, and share a favorite species to nest in: the jumping cholla. Because of this, interspecific conflict is frequent. Fights over food are rare, but fights to protect fledglings are heated. They will vigorously work to destroy each other's nests. Despite this, nests of curve-billeds and cactus wrens may still be concurrently and successfully raised even feet away from each other. Anderson & Anderson noted a minimum nest distance of a highly unusual 6 inches (neither nest was destroyed by the either throughout the entire season), although average interspecies nest distances were well over a hundred feet. Nest destruction is almost always unsuccessful, and less intense, during breeding times, as both species adamantly defend their own nests. Once breeding season wanes, and fledglings emerge, competition becomes more fierce.:168-187
Young are born asynchronously with their eyes closed, and are mostly bald, with sparse patches of fuzzy white down. The young are fed (mostly insects) by both parents. Young make begging vocalizations at least as early as 2 days old, with the vocalizations evolving as the chicks age. Chicks are dependent on their parents for the first three weeks after hatching. Nestlings open their eyes between 6 and 8 days, and grow feathers starting at 8 days post hatching (although quills emerge as early as 2 days after hatching). Adult feather length is reached by 20 days old. Nestlings reach adult weight at about 38 days, and gain independence between 30 and 50 days post-hatching. The young can stay in the parent's territory for a while after fledging, but will be driven off by the next breeding season. Juveniles that stay around can help take care of successive broods. Cactus wrens can live to 7 years in the wild, but average lifespan is 2 years for males, and 1.3 years in females.
The cactus wren primarily eats insects, including ants, beetles, grasshoppers, termites, and wasps. The cactus wren will also take seeds, fruits, nectar, and even small reptiles. Foraging begins late in the morning and is versatile; the cactus wren will search under leaves and ground litter and overturn objects in search of insects, as well as feeding in the foliage and branches of larger vegetation. Some individuals have even learned to take insects caught in vehicle radiator grills. Increasing temperatures cause a shift in foraging behavior to shady and cooler micro-climates, and activity slows during hot afternoon temperatures. This is partly to conserve water and keep cool during hot days, but also because their insect prey is more sluggish and thus easier to catch in cool temperatures. Almost all water is obtained from food, and free-standing water is rarely used even when found. The cactus wren can survive as a true xerophile, existing without any free water. Eating cactus fruits is an important source of water, and individuals have even been seen drinking cactus sap from wounds inflicted by Gila woodpeckers. Cactus wrens also sip nectar from saguaro blossoms and eat insects trapped within, serving as pollinators in the process.:187
Parents provide whole insects to young, although they may first remove wings or legs. One study found that the average caloric needs of a developing chick required about 15 medium sized grasshoppers per day. Cactus wrens generally feed and live in pairs, or in family groups from late spring through winter. Flocks of cactus wrens are reported to form, but seem to do so only rarely. Flocking has only been observed in areas of abundant forage, and does not last long.:18-19 As ground feeders they spend much of their time on the ground and are not exceptionally strong fliers, with any flights being somewhat erratic – switching between rapid wing flapping and gliding.
Nests built in cactus provide a degree of protection to young, yet even in cactus, young wrens are vulnerable to predation by coachwhip snakes. When threatened, young in nests were observed to try to blend in with the nest, and flattened themselves against the nest walls. Adults are preyed upon by coyotes, foxes, hawks, bald eagles, domestic cats, and greater roadrunners. Upon detection of predators, cactus wrens will usually mob the predator and vocally scold it. They may also chase ground based predators and intruders. Predator alarm calls are usually a low buzz, or sometimes a staccato "tek" which is repeated. In response to birds of prey adults may attempt to move closer to the ground or leave calling spots.
Relationship to humans
The cactus wren is the state bird of Arizona. It was designated as such on March 16th of 1931, by the Arizona State Legislature, as House Bill 128. The bill refers to the bird as both the "Cactus Wren" and "Coues' Cactus Wren". The State Legislature specifically designated subspecies couesi as the state bird.:1
The cactus wren is abundant in most of its native range, although its numbers may be declining in Texas and southern California. The IUCN classifies its population as "decreasing", but ranks the species conservation status as Least Concern. Current population estimates put the species at about 7 million individuals, with slightly more than half residing in Mexico, and the rest in the United states. Populations declined 55% between 1966 and 2015, but decline is not consistent across the range. U.S. populations have decreased more than Mexican ones, but some local populations – such as in Nevada, New Mexico, and the Chihuahuan desert – populations have actually increased. Populations in Texas have faced the steepest declines, followed by Arizona and California.
Coastal populations in southern California face threats due to habitat loss as a result of suburban development. Populations have been highly fragmented due to urbanization, which may lead to genetic differentiation among isolated populations and could threaten overall species viability. Similar species which nest in coastal sage scrub (the preferred nesting habitat of coastal cactus wrens) have faced high levels of extinction. California subspecies C. b. sandiegensis was petitioned to be listed as federally endangered in 1990, but was not due to taxonomic disputes as to whether sandiegensis was actually distinct from the rest of the cactus wren population. Sandiegensis is however listed as a "California Species of Special Concern."
Across its range, habitat fragmentation is a major problem. Urban populations have faced especially steep declines. Habitat degradation at the edge of the habitat/urban interface led to general population loss. Study showed that fire had an outsized impact on cactus wrens due to their territoriality, with populations persisting only in unburned pockets. These issues are compounded by the apparently poor ability of the cactus wren to disperse: each subsequent generation of wrens will usually not travel great distances to establish territory. Most young, once chased out of their parents territory, will generally establish their new territory directly adjacent to their parents. Other issues include invasive grasses, which take up valuable foraging space, as the wren only forages in mostly open areas. Domestic cats also take a high proportion of birds in urban settings. Despite the threats it faces, the cactus wren has proved adaptable, especially to human modifications. It can survive in degraded habitat, as long as suitable nesting habitat, such as spiny cactus, remain.
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- Kroodsma, Donald; Brewer, David (2005), "Family Troglodytidae (Wrens)", in del Hoyo, Josep; Elliott, Andrew; Christie, David, Handbook of the Birds of the World. Volume 10, Cuckoo-shrikes to Thrushes, Barcelona: Lynx Edicions, pp. 356–447, ISBN 978-84-87334-72-6
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- Proudfoot, Glenn A.; Sherry, Dawn A.; Johnson, Steve (2000). Poole, A.; Gill, F., eds. "Cactus Wren (Campylorhynchus brunneicapillus)". The Birds of North America Online. doi:10.2173/bna.558. ISSN 1061-5466.
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- Facemire, Charles F.; Facemire, Michael E.; Facemire, Mark C. (November 1990). "Wind as a Factor in the Orientation of Entrances of Cactus Wren Nests". The Condor. 92 (4): 1073. doi:10.2307/1368745.
- The Atlas of world wildlife. Huxley, Julian, 1887-1975., Zoological Society of London., World Wildlife Fund. Goldaming, Surrey, England: Colour Library Books Ltd. 1988. p. 28. ISBN 0862834902. OCLC 153266629.
- "Arizona's Audacious State Bird, the Cactus Wren | Tucson Audubon Society". Retrieved 13 February 2019.
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