Carolina wren

The juvenile T.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][16] 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.[16]

Sketches of Thryothorus ludovicianus, T.l. lomitensis, and Thryomanes bewickii (Bewick's wren) and one of its subspecies

Survival rates differ by region. A male captured in Arkansas lived to be at least 73 months old, and in Alabama, the oldest female and male captured were six and ten years old, respectively. In a survival probability mark-and-recapture study conducted within the Southeastern United States from 1992 to 2003, roughly 90 percent of the banded wrens died within 10 years.[17]

The easiest species to confuse with the Carolina wren is Bewick's wren,[18] which differs in being smaller but with a longer tail, grayer-brown above and whiter below. The Carolina and white-browed wrens differ from the house wren in being larger, with a decidedly longer bill and hind toe; their culmen has a notch behind the tip.[19]

Carolina wrens sing year round and at any point during the daytime, with the exception of performing during the most harsh weather conditions.[23] Males alone sing, and have a repertoire of at least twenty different phrase patterns and on average, thirty two.[24][25] 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 as teakettle-teakettle-teakettle and cheery-cheery-cheery.[16][23] Various descriptions of the teakettle song include whee-udel, whee-udel, whee-udel, che-wortel, che-wortel and túrtee-túrtee-túrtee and familiar names and phrases such as sweet heart, sweet heart, come to me, come to me, sweet William, and Richelieu, Richelieu.[16]

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.[26] 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.[26]

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.[24]

Carolina wren on Rutland Township Forest Preserve

Different subspecies have variations in songs and calls, such as miamensis having a more rapid song that contains more notes than the races that are further north.[3]

Their songs can be confused with the Kentucky warbler. The song patterns are similar, but the warbler's songs are described as richer, with more ringing and a hurried pace.[23] Other bird species with songs described as akin to the wren are the flicker, Baltimore oriole, grey catbird, and more specifically the peto, peto, peto call of the tufted titmouse and the whistle of the northern cardinal.[16] Occasionally, the wrens mimic other species; in Pennsylvania 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.[15]

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.[27] 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.[28] Not all birds within their territory are potential enemies. Some species of birds that are neighbors are designated as 'dear-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.[29] When protecting their nest, alarm calls are the general response. The wrens judge the size of the potential threat, such as a blue jay and avoid the risk of injury when attacking.[30] Countersinging produced by intruder birds is more likely to be taken as an aggressive threat to male Carolina wrens.[31]

Both males and females utilize calls in alarm situations, especially in territorial disputes and encounters with predators. Males alone produce the cheer call, which can sound indistinct. In southern regions of their range, the sound males use in alarm disputes is a ringing pink or p'dink sound. Females are the only ones that can perform the paired dit-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 males cheer chant. The chatter is used exclusively with territorial encounters with male song, and the song can either follow or overlap her mate's song.[24][32]

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 of invertebrates, such as beetles, true bugs, grasshoppers, katydids, spiders, ants, bees, and wasps. Small lizards and tree frogs also make up the carnivorous portion of their diet. Vegetable matter, such as fruit pulp and various seeds, makes up a small percentage of their diet. In the northern portion of their range, they frequent bird feeders.[3][23]

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.[23] While moving abruptly, they pause momentarily for chattering or singing.[16] When stationary, they move in twitched motions, jerking their breast around.[23] They also sun- or sand-bathe.[33] The wrens also displays a skittish behavior when encountered by humans, 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.[16] Other movements involve being capable of crawling like a creeper and hanging upside-down like a nuthatch.[23]

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][23]

Carolina wren nesting in a duck nestbox

Carolina wrens are both genetically and socially monogamous and will usually mate for life. Mate changing is rare,[15] 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.[34] Along with thermoregulatory benefits, roosting is thought to reinforce pair-bonding and prevent divorce between mates.[35]

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 a tractor in everyday use.[3][16] 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.[14][21] The clutch size is generally 3 to 6 eggs, but can reach as high as seven in Texas.[3][14] 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.[17]

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.[36]