About Thryothorus ludovicianus (Latham, 1790)
Carolina wren (Thryothorus ludovicianus) measures 12.5 to 14 cm (4.9 to 5.5 in) in length, has a 29 cm (11 in) wingspan, and weighs approximately 18 to 23 g (0.63 to 0.81 oz). It is classed as a fairly large wren, and is the second largest wren species found in the United States, only smaller than the cactus wren. Standard measurement ranges for the species are as follows: wing chord 5.4 to 6.4 cm (2.1 to 2.5 in), tail 4.5 to 5.6 cm (1.8 to 2.2 in), culmen 1.4 to 1.8 cm (0.55 to 0.71 in), and tarsus 2 to 2.3 cm (0.79 to 0.91 in). Sexual dimorphism is slight, with males being larger than their female mates. One study of 42 mated pairs found that every male except one was larger than his paired female; on average, males were 11 percent heavier and had longer wing chords. Multiple physical differences exist between the species' subspecies. For the nominate subspecies T. l. ludovicianus, the crown is rich brown, shifting to a more chestnut color on the rump and upper tail coverts. Shoulders and greater coverts are rich brown, with a row of small white dots on the lesser primary coverts. Secondary coverts are rich brown with darker brown barring across both webs; barring on the primaries is restricted to the outerwebs, and is darker and more noticeable. The rectrices are brown with 18 to 20 bars that cross the entire tail. A white supercilium stripe is thinly bordered with black above and below, and extends above and beyond the shoulders. Ear coverts are speckled gray and grayish-black. The chin and throat are gray, shifting to buff on the chest, flanks, and belly; the flanks and belly are a warmer shade of buff than the chest. Underwing coverts are grayish buff. The iris is reddish-brown; the upper mandible is lemon-colored, paler at its base, matching the lower mandible. Legs are flesh-colored. Compared to T. l. ludovicianus, other subspecies differ in the following ways: T. l. berlandieri is slightly smaller in build but has a larger bill, with duller brown upperparts and deeper colored underparts; T. l. lomitensis is duller in overall color than both T. l. ludovicianus and T. l. berlandieri, with underparts that are either pale or almost white; T. l. miamensis has darker rusty chestnut upperparts and deeper colored underparts; T. l. burleighi is duller and sootier, with less distinct tail markings; T. l. mesophilus has paler underparts and a whiter supercilium; T. l. tropicalis is darker than all other subspecies, and has heavier barring than T. l. berlandieri. Carolina wrens are largely resident, and only disperse beyond their usual range after mild winters. They sporadically breed as far north as Maine and Quebec following mild winters. In some parts of their potential range, such as most of Iowa, prolonged periods of snow limit potential northward expansion. Permanent breeding ranges extend from eastern Nebraska, southern Michigan, southeast Ontario and the New England states in the north, south to Mexican states Coahuila, Nuevo León, San Luis Potosí, and Tamaulipas, and the Gulf Coast of the United States. Local, infrequent, likely breeding occurrences have been recorded in southeast South Dakota, central Kansas, eastern Colorado, western Oklahoma, Texas, and as far north as Maine and New Brunswick. Occasional vagrants have been spotted in Colorado, New Mexico, Arizona, Wyoming, South Dakota, Manitoba, Nova Scotia, and the Gulf of St. Lawrence. Over the past few centuries, the Carolina wren's range has expanded northward and westward across multiple regions. In Massachusetts, the species expanded westward and northeastward from its former southeastern range over approximately 35 years. In New York, the population tripled over roughly 25 years. In the midwestern states of Ohio and Michigan, population numbers have increased since the mid-1800s and early 1900s, respectively. Expansion around Ontario has occurred since early reports in 1890 and 1905. Proposed explanations for this range expansion include fewer frequent winter storms in the 20th century, expanded forest habitats, and Carolina wrens utilizing urban areas with bird feeders, especially during winter. From 1966 to 2015, the Carolina wren saw an annual population increase of greater than 1.5% across most of its northern range, extending from southern Maine to southern Nebraska. Carolina wrens adapt to a wide variety of habitats. Their natural habitats include multiple types of woodland, such as oak hardwoods, mixed oak-pine woodlands, ash and elm woods, and hickory-oak woodlands with abundant tangled undergrowth. Their preferred habitats are riparian forest, brushy edges, swamps, overgrown farmland, suburban yards with thick abundant shrubs and trees, and parks. The species shows a preference for dilapidated buildings and unkempt yards in human-modified areas. Subspecies T. l. burleighi and T. l. mesophilus inhabit slash pine and palmetto habitats.
