| Carolina wren | |
|---|---|
 | |
| Houston, Texas | |
| Recorded inCape May, New Jersey, US | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Passeriformes |
| Family: | Troglodytidae |
| Genus: | Thryothorus Vieillot, 1816[2] |
| Species: | T. ludovicianus |
| Binomial name | |
| Thryothorus ludovicianus (Latham, 1790) | |
| Subspecies[3] | |
List
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| Range of the Carolina wren (T. ludovicianus) | |
| Synonyms[4] | |
Sylvia ludoviciana(Latham, 1790) | |
TheCarolina wren (Thryothorus ludovicianus) is a species ofwren that is common in the Eastern United States, the extreme south of Ontario, Canada, and the extreme northeast of Mexico. Severe winters restrict the northern limits of their range, while favorable weather conditions lead to a northward extension of their breeding range. Their preferred habitat is in dense cover in forest, farm edges, and suburban areas. This wren is the state bird of South Carolina.
Seven recognized subspecies occur across the range of these wrens and they differ slightly in song and appearance. The birds are generally inconspicuous, avoiding the open for extended periods of time. When out in the open, they energetically investigate their surroundings and are rarely stationary. After finding a mate, pairs maintain aterritory and stay together for several years. Both males and females give out alarm calls, but only males sing to advertise territory. Carolina wrens raise multiple broods during the summer breeding season, but can fall victim tobrood parasitism bybrown-headed cowbirds, among other species. Some populations have been affected by mercury contamination.
The Carolina wren was first described under the name ofSylvia ludoviciana byJohn Latham in 1790.[3][note 1]Louis Pierre Vieillot considered all wrens under the genusTroglodytes and called the Carolina wrenTroglodytes arundinaceus, but placed it subsequently in a separate genusThryothorus (initially misspelledThriothorus)[2] that he created in 1816.[7]
The genus nameThryothorus is ofGreek origin from the combination of the noun θρύον :thrýon ("rush, reed") and the adjective θοῦρος :thoũros ("rushing, impetuous"; derivative of verb θρῴσκειν :thrōskein to leap up, spring, jump at). Thus,Thryothorus means 'reed jumper'.
Itsspecific nameludovicianus is a post-classicalLatin term forLudovicus (derivative fromLouis XIV) that means 'ofLouisiana' that identifies the locality of the specimen collected nearNew Orleans.[8][9]
Thryothorus used to be the largest genus in the family Troglodytidae, with 27 species, but molecular phylogenetic studies revealed that it represented apolyphyletic assemblage of at least four independentclades now recognized at the genus level.[10][11] The Carolina wren is now the only species within this genus.[12]
The seven recognized subspecies of the Carolina wren are:[3][13]
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At 12.5 to 14 cm (4.9 to 5.5 in) long, with a 29 cm (11 in) wingspan and a weight of about 18 to 23 g (0.63 to 0.81 oz), the Carolina wren is a fairly large wren; the second largest in the United States species after thecactus wren. Among standard measurements, thewing chord is 5.4 to 6.4 cm (2.1 to 2.5 in), thetail is 4.5 to 5.6 cm (1.8 to 2.2 in), theculmen is 1.4 to 1.8 cm (0.55 to 0.71 in) and thetarsus is 2 to 2.3 cm (0.79 to 0.91 in).[3]Sexual dimorphism is slight with males being larger than their mates. A study indicated that of 42 mated pairs, every male but one was larger than the female of the pair. The males were on average 11 percent heavier along with having longer wing chords.[16]
Several differences are seen among the subspecies. ForT. l. ludovicianus, thecrown is rich brown that appears more chestnut-colored on itsrump and upper tail coverts. Shoulders and greatercoverts are a rich brown, with a series of small white dots on the lesser primary coverts. The secondary coverts are rich brown with a darker brown barring on both webs; the bars on the primaries are on the outerwebs only, but darker and more noticeable. Therectrices are brown with 18 to 20 bars that span across the tail. The whitesupercilious streak borders thinly with a black above and below, and extends above and beyond its shoulders. The ear coverts are speckled gray and grayish-black. Its chin and throat are grey that becomes buff on its chest, flank and belly, though the latter two are of a warmer color. The underwing coverts sport a grayish buff color. Itsiris is reddish-brown, theupper mandible is lemon-colored and paler at the base andlower mandible. The legs are flesh-colored.[3]
As for the other subspecies in contrast toT. l. ludovicianus,T. l. berlandieri is of a slightly smaller build, but possesses a larger bill, the upperparts are duller brown with deeper colored underparts,T. l. lomitensis is of a duller color (than eitherludovicianus orberlandieri) with its underparts either pale or almost white,T. l. miamensis contains darker rusty chestnut upperparts and deeper colored below.T. l. burleighi is duller and sootier with less distinct tail markings,T. l. mesophilus has paler underparts and a whiter supercilium, andT. l. tropicalis is darker than all races, and contains heavier bars thanT. l. berlandieri.[3]
The juvenileT.l. ludovicianus is similar in appearance, but the plumage is generally paler; a softer texture, buff-tipped wing coverts, and a paler superciliary streak.[3][17] In August and September, the partial plumage molt for the post-juvenile wrens is darker in color and affects the contour plumage, wing coverts, tail and develops a whiter superciliary stripe. The post-nuptial molt for adults in the same time period is more pronounced in color than the spring molt, with both sexes similar in appearance.[17]
Survival rates differ by region. A male captured inArkansas lived to be at least 73 months old, and inAlabama, the oldest female and male captured were six and ten years old, respectively. In a survival probabilitymark-and-recapture study conducted within theSoutheastern United States from 1992 to 2003, roughly 90 percent of the banded wrens died within 10 years.[18]
The easiest species to confuse with the Carolina wren is Bewick's wren,[19] which differs in being smaller but with a longer tail, grayer-brown above and whiter below. The Carolina and white-browed wrens differ from thehouse wren in being larger, with a decidedly longerbill and hind toe; theirculmen has a notch behind the tip.[20]
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These birds are largely resident, and will only disperse beyond their range after mild winters.[3] Carolina wrens sporadically breed as far north asMaine andQuebec after mild winters.[3][21] In certain parts of their range, such as most ofIowa, prolonged periods of snow can curtail potential expansion.[22] Permanent breeding locations range from easternNebraska, southernMichigan, southeastOntario and theNew England states to Mexican states such asCoahuila,Nuevo León,San Luis Potosí andTamaulipas and theGulf Coast of the United States.[18] Local occurrences with infrequent and likely breeding locations include southeastSouth Dakota, centralKansas, easternColorado, westernOklahoma andTexas as far asMaine andNew Brunswick.[18] There have been occasional vagrants spotted inColorado,New Mexico, andArizona,Wyoming,South Dakota,Manitoba,Nova Scotia, and theGulf of St. Lawrence.[3][21]
The range of the wrens increased northward and westward in several regions over the past few centuries. InMassachusetts, the wrens had expanded westward and northeastward from its former southeastern location in approximately 35 years, inNew York the population increased three-fold in roughly 25 years, while in the midwest states ofOhio andMichigan, numbers have increased since the mid-1800s and early 1900s, respectively.[18] Expansion aroundOntario occurred since early reports in 1890 and 1905. Explanations given include infrequent winter storms in the 20th century, expanded forest habitats, and the wrens taking advantage of urban areas containing feeders, especially in winter.[18] From 1966 to 2015 the Carolina wren experienced a greater than 1.5% annual population increase throughout most of its northern range, extending from southern Maine to southern Nebraska.[23]
Carolina wrens adapt to various habitats. Natural habitats include various types of woodland such asoak hardwoods and mixed oak-pine woodlands,ash andelmwoods, hickory-oak woodlands with a healthy amount of tangled undergrowth.[3][24] The preferred habitats areriparian forest,brushy edges,swamps, overgrownfarmland, andsuburban yards with abundant thick shrubs and trees, and parks.[3][24] It has an affinity for dilapidated buildings and unkempt yards in man-made areas.[24] Subspeciesburleighi andneophilus inhabitslash pine andpalmettos.[3][24]
Carolina wrens sing year round and at any point during the daytime, with the exception of performing during the most harsh weather conditions.[24] Males alone sing, and have a repertoire of at least twenty different phrase patterns and on average, thirty two.[25][26] One of these patterns is repeated for several minutes, and although the male's song can be repeated up to twelve times, the general number of songs range from three to five times in repetition. While singing, the tail of the birds is pointed downward. Some general vocalizations have been transcribed asteakettle-teakettle-teakettle andcheery-cheery-cheery.[17][24] Various descriptions of theteakettle song includewhee-udel, whee-udel, whee-udel,che-wortel, che-wortel andtúrtee-túrtee-túrtee and familiar names and phrases such assweet heart, sweet heart,come to me, come to me,sweet William, andRichelieu, Richelieu.[17]
Males are capable of increasing their repertoire through song learning, but due to their sedentary nature and territorial defense habits, the song learning must occur within the first three months of life.[27] Geographic barriers affect song repertoire size from male wrens, as one study indicated that distances separated as close as 3 kilometres (1.9 mi) by water barriers can have the same effect as that of a distance of 145 kilometres (90 mi) in the mainland with no barriers.[27]
Female Carolina wrens possess song control regions that would appear to make them capable of singing with repertoires like the male. Due to vocalizations that they occasionally make with the male, it has been suggested that song perception plays a role and is of behavioral relevance.[25]
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Different subspecies have variations in songs and calls, such asmiamensis having a more rapid song that contains more notes than the races that are further north.[3]
Their songs can be confused with theKentucky warbler. The song patterns are similar, but the warbler's songs are described as richer, with more ringing and a hurried pace.[24] Other bird species with songs described as akin to the wren are theflicker,Baltimore oriole,grey catbird, and more specifically thepeto, peto, peto call of thetufted titmouse and the whistle of thenorthern cardinal.[17] Occasionally, the wrens mimic other species; inPennsylvania this trait has caused the bird to be also known as the 'mocking wren'.[3]
A 2006 study suggested that the correlation of tail length and body size in males, wing length in females, and lifespan for both sexes were signs of individual quality, and the wrens of high quality tend to mate with like individuals. The courting and antagonistic encounters that involve the tail fanning and wing drooping was suggested to be a possible signaling use. Age and life experience are not thought of as significant for potential mates due to their relatively short lifespan and sedentary lifestyle. Due to the large size of male wrens and the male's vigor in defending its territory, intrasexual selection was given as a possible explanation for the sexual dimorphism.[16]
Both sexes are involved in defending the territory. One aspect of territorial defense involves identifying the proximity of the threat based on the loudness of bird song as well as the level of degradation of the calls. In experiments involving playback, the wrens are capable of discriminating between degraded and undegraded songs, as well as degraded songs in the same acoustic conditions, and can detect changes of acoustic properties within their territories, such as songs under foliage.[28] Song degradation can also be used to determine the proximity of potential intruders. If the song of a bird appears to be degraded, the wrens will assume that the threat is distant and not respond; if the song is not degraded, they respond by attacking.[29] Not all birds within their territory are potential enemies. Some species of birds that are neighbors are designated asdear enemies by the wrens, and the responses to neighbors and intruders in their territories differ by the season. In spring, the wrens respond more aggressively toward neighbors, though in the fall, no major discrepancy in responses is shown.[30] When protecting their nest, alarm calls are the general response. The wrens judge the size of the potential threat, such as ablue jay and avoid the risk of injury when attacking.[31] Countersinging produced by intruder birds is more likely to be taken as an aggressive threat to male Carolina wrens.[32]
Both males and females utilize calls in alarm situations, especially in territorial disputes and encounters with predators. Males alone produce thecheer call, which can sound indistinct. In southern regions of their range, the sound males use in alarm disputes is a ringingpink orp'dink sound. Females are the only ones that can perform the paireddit-dit or chatter sounds. The former can be used in territorial disputes with predators, and with at least northern populations the songs are used in alternation with the malescheer chant. The chatter is used exclusively with territorial encounters with male song, and the song can either follow or overlap her mate's song.[25][33]
Carolina wrens spend the majority of their time on or near the ground searching for food, or in tangles of vegetation and vines. They also probe bark crevices on lower tree levels, or pick up leaf-litter in order to search for prey. Their diet consists ofinvertebrates, such asbeetles,true bugs,grasshoppers,katydids,spiders,ants,bees, andwasps. Smalllizards andtree frogs also make up the carnivorous portion of their diet. Vegetable matter, such as fruit pulp and variousseeds, makes up a small percentage of their diet. In the northern portion of their range, they frequentbird feeders.[3][24]
Carolina wrens are wary, and are more often heard than seen. When on the ground, they move in jerky hops pillaging through various objects, whether man-made or natural.[24] While moving abruptly, they pause momentarily for chattering or singing.[17] When stationary, they move in twitched motions, jerking their breast around.[24] They also sun- or sand-bathe.[34] The wrens also displays a skittish behavior when encountered byhumans, as they can be seen thrusting off into cover slowly if approaching is detected. However, they occasionally seek out humans that are near, so long as there is no movement from them.[17] Other movements involve being capable of crawling like acreeper and hanging upside-down like anuthatch.[24]
Flights are generally of short duration, rapid, low-leveled, and wavelike. The wings during flight are flapped rapidly, and are frequently used during foraging. They are also capable of flying vertically from the base of a tree to the top in a single wing assisted bound.[3][24]
Carolina wrens are both genetically and sociallymonogamous and will usually mate for life. Mate changing is rare,[16] and there has been one possible observation of polygamy.[3] During the winter season, males are more responsible for guarding the territory. Females vary in succeeding to maintain winter territories without a mate.[3] It has been suggested that the possibility of desertion and decline in care-taking from males along with the need for security in resources year-round prevent extra pair copulations from females, as the mortality rate for Carolina wrens peaks during the winter.[35] Along with thermoregulatory benefits,roosting is thought to reinforce pair-bonding and prevent divorce between mates.[36]
The nests are arch-shaped structures with a side entrance and built of dried plants or strips of bark, as well as horsehair, string, wool and snake sloughs. The male obtains nesting materials while the female remains at the site to construct the nest. Nests are located in fragmented or complete cavities in trees, or in man-made structures such as bird-boxes, buildings, tin cans, mailboxes or unorthodox places such as pockets of hanging jackets in sheds or in atractor in everyday use.[3][17] Nests are from 1–3 m (3.3–9.8 ft) from the ground and are rarely higher. They occasionally can be built in sloping locations or at ground level.[3]
Egg laying dates and clutch size vary by region; in Texas the time period is from late February to late August, in Iowa it ranges from late April to June.[15][22] The clutch size is generally 3 to 6 eggs, but can reach as high as seven in Texas.[3][15] The eggs are creamy white with brown or reddish-brown spots, and are more heavily marked at the broad end.[3] The eggs are incubated by the female for 12–16 days. After the young hatch, they are fed exclusively on invertebrates and they fledge in 12–14 days. As many as three broods may be raised by a pair in a single breeding season.[3] In one study, three of the 70 fledglings remained or defended territory adjacent to the natal area.[18]
Male and females are involved in the process of provisioning at similar rates throughout most nest stages, with the males providing slightly more in the nestling stages. Both sexes increase their provision rates as the nestlings grow in age.[37]
Although Carolina wrens are fairly common,brood parasitism by thebrown-headed cowbird is common, with up to 25% of Carolina wren nests being affected in certain regions such asOklahoma andAlabama.[3][18] Cowbird parasitism peaks in April at 41%, and is as low as 8% and 0% in July and August, respectively. Female cowbirds sometimes eject Carolina wren eggs before laying their own, and even if host eggs are retained, the size of cowbird eggs negatively affect the hatching success of wren eggs. As a result, cowbirds may have a significant impact on the reproductive success of wrens.[3][18] The feeding rate for cowbird nestlings is higher than wren feeding rates, and some have been raised to independence.[18] This also can be detrimental to the survival of wren nestlings.[18] A rare instance of brood-parasitism by ahouse finch has been recorded.[18][38] The rate of brood parasitism is thought to be lower in more natural and concealed nesting locations.[18] Body parasites such as the larvae ofblowflies feed on nestlings and the blood loss weakens nestlings.[18] Fellow species of wren such as Bewick's wren and thewinter wren compete for nesting locations and food, respectively.[18]
InVirginia, some Carolina wrens populations show high levels ofmercury in their blood and this is acquired from feeding all-year-round on spiders.[39][note 2] Spiders being at a highertrophic level contain a higher concentrations of mercury (throughbiomagnification) than herbivorous invertebrates. As these wrens are year-round residents, they are at a higher risk than other species to acquire mercury in their blood. Nest abandonment and failure to raise young are more common with higher mercury content.[39] Exposure, and prolonged periods of cold, ice, and snow is thought to affect the wren nestling and adult populations, respectively.[18] Wrens that outlast those winters reside in sheltered areas during the season.[17]
Among the top predators of adult Carolina wrens aredomestic cats, and snakes such as thetimber rattlesnake.[40][41]Raccoons andblack rat snakes also feed on wren eggs and nestlings.[18]
In 1930, the South Carolina Federated Women's club adopted the Carolina wren as the unofficial state bird over theeastern mourning dove and pushed for its official state adoption until 1939, when the South Carolina Legislature named thenorthern mockingbird as the state bird. In 1948, the legislature repealed their previous decision, and the wren became the official state bird.[42]
In 2000, the Carolina wren was featured on the back of the South Carolina edition of the50 State Quarters.[43]
