Kirtland's warbler (Setophaga kirtlandii), also known in Michigan by the common name jack pine bird, or the jack pine warbler, is a small songbird of the New World warbler family (Parulidae). Nearly extinct just years ago, populations have recovered due to the conservation efforts of the Kirtland's Warbler Conservation Team and its members. The birds require large areas, greater than 160 acres (65 hectares), of dense young jack pine for breeding habitat. This habitat was historically created by wildfire, but today is created through the harvest of mature jack pine (Pinus banksiana), and planting of jack pine seedlings.
The population of the species spends the spring and summer in its breeding range in the Great Lakes region of Canada (Ontario) and the United States (Wisconsin and Michigan, especially in the northeastern Lower Peninsula), and winters in the West Indies.
Taxonomy This species was first recorded by Europeans relatively late for a bird from eastern North America. The first specimen was shot at sea somewhere between the Abaco Islands of The Bahamas and Cuba in mid-October 1841 by the ornithologist Samuel Cabot III. However, the specimen was unrecognized as a new species in the private collection of Cabot's father, Boston merchant Samuel Cabot Jr., until it made its way to the Museum of the Smithsonian Institution in the 1860s.
Ten years later the holotype, a juvenile male, was shot on Jared Potter Kirtland's farm near Cleveland, Ohio, in mid-May 1851. It was used to formally describe the species as Sylvicola kirtlandii by Spencer Fullerton Baird in 1852. Baird first attributed the collection to Charles Pease (Kirtland's son-in-law) in his 1852 description, but by 1858 he had changed his story and was attributing it to Kirtland.
In 1858 Baird moved the species, still then only known from his single specimen, to the genus Dendroica, where it remained until the 2010s, when it (and all other Dendroica warblers) was merged into the genus Setophaga.
By 1865 only four individuals were known to have been collected. Baird lists the male specimen from the Cabot collection, the holotype, a first female specimen shot in 1860 near Cleveland and preserved by R. K. Winslow, and a fourth (which Winslow mentioned had also been killed near Cleveland but had not been preserved). Local naturalist Philo Romayne Hoy also mentioned having possibly seen the species once near the village of Racine, Ohio, in the 1850s.
Etymology Baird decided to name the bird after Jared Potter Kirtland: "a gentleman to whom, more than any one living, we are indebted for a knowledge of the Natural History of the Mississippi Valley". The generic epithet Setophaga is from the genitive case of Ancient Greek σής, transliterated as , meaning "moth", and , meaning "eating".
Description
Male Kirtland's warblers have bluish-grey upper body parts, with dark streaks on the back, yellow bellies, and dark streaks on the flanks and sides. It has black lores (cheeks) and a distinctive, large and conspicuous broken white eye ring, which it only shares with Setophaga coronata. Females and juveniles are similar, but are browner on the wings and back and are not as boldly or brightly marked. It frequently bobs its tail up and down, which is uncommon in northern warblers. At and , it is the largest of the numerous warblers formerly classified in the genus Dendroica and is now the largest of the 35 or so species in the currently-accepted Setophaga genus. The Kirtland warbler has a wingspan of . Its mating song is a loud chip-chip-chip-too-too-weet-weet often sung from the top of a snag (dead tree) or northern pin oak (Quercus ellipsoidalis) clump. This song can be heard over away in good conditions. In its overwintering grounds it does not sing but makes loud "chip" noises from low in dense bushes.
The eggs are a "delicate" pinkish white when fresh, fading to a dull white after a time. There are a few scattered sprinkles in various shades of brown and pink, these sprinkles and blotches concentrated at the top or form a sort of wreath at the larger end. The egg is not very glossy. It is 18 by 14mm in size. The shell is very thin.
Similar species Baird compared and found it most similar to Setophaga coronata, finding it best distinguishable by having a nearly uniformly yellow belly, no conspicuous yellow rump or crown, less black in the feathers of the crown, and a considerably larger and stouter bill and feet. Henninger mentions he finds it to have a certain resemblance to S. magnolia. In The Bahamas it may be misidentified with S. dominica flavescens.
Hybrids In late October 1997 a large hybrid Setophaga warbler was netted in the low elevation dry scrublands of the southernmost Dominican Republic, which based on morphology (plumage colour and anatomical measurements of size) and geography was most likely a hybrid between S. kirtlandii and S. fusca.
Distribution It was originally only known from Kirtland's home state of Ohio. In the mid 20th century the breeding range of Kirtland's warbler was reduced to a very limited area in the north of the Lower Peninsula of Michigan. In recent years, breeding pairs have been found in the Upper Peninsula of Michigan, Wisconsin, and southern Ontario due to the expanding population. The birds winter in Cuba, The Bahamas and the nearby Turks and Caicos Islands, where they are found on all islands investigated. A number also overwinter on Hispaniola, in the Dominican Republic. Overwintering birds have been collected and sighted a number of times in Florida. It has been recorded as a rare accidental on Bermuda and Jamaica, and there is an uncorroborated report from coastal Mexico.Mayfield, Harold F (1992). Kirtland's Warbler. In: Poole A, Stettenheim P, Gill F (editors) (1992). The Birds of North America, No. 19. Philadelphia, Pennsylvania: The Academy of Natural Sciences / Washington, District of Columbia: The American Ornithologists' Union It has also been observed in the summer in Québec, although it is not known to breed there.
Individuals first migrate from The Bahamas west to Florida and South Carolina in the second half of April to early May, and from there move further northwest and westwards until they reach the Mississippi River, which they then follow upstream to the mouth of the Ohio River during May. They reach their breeding grounds early in June, and then leave their breeding range between August and October.
Breeding range and habitat The Kirtland's warbler has a highly restricted breeding range in the Great Lakes region, breeding in jack pine (Pinus banksiana) forests in northern Michigan, Wisconsin, and Ontario. Its typical breeding habitat consists of large stands of young jack pine, about 4–25 years old and 5–20 feet (1.5–6.1 m) tall, with dense clumps of trees interspersed with small grassy openings, sedges, ferns, and low shrubs, usually on sandy glacial outwash plains. Females build nests on the ground under dense tree cover, commonly concealed by grasses, sedges, other ground vegetation, or the low branches of young jack pine or oak. Although the species is strongly associated with young jack pine habitat, researchers have reported that Kirtland's warblers have also bred in young red pine-dominated plantations in central Wisconsin where habitat structure approximates that of young jack pine stands.
Habitat In their winter habitat, they have been found primarily in low "coppice" habitat, especially areas which have been cleared for slash-and-burn agriculture but have regrown after abandonment (98% of all records), with a preference for dense shrubbery with small openings here and there, no canopy and low ground cover. It has otherwise been found in all habitats on the islands, including, albeit uncommonly, suburban gardens and Bahamian pineyards, with the exception of high coppice which has never been clear cut -it has never been seen here. With rare exceptions this bird is almost always sighted from the ground to high (98%).
For breeding habitat it requires large areas of young jack pine on sandy soil. Kirtland's warblers occur in greatest numbers in large areas that have been clear cut or where a large wildfire has occurred. For breeding they require stands of young (6 to 20 year old, 2–4 m high) jack pine trees. Other common plants in this habitat are blueberry (Vaccinium angustifolium), sweet fern (Comptonia peregrina), Canada mayflower (Maianthemum canadense) and various grasses. Although it was initially believed to exclusively require jack pine stands, more recent research has found that the bird will also breed in some places in young stands of red pine (Pinus resinosa) of 10 to 15 years old. When the pine stands grow so tall so as to lose their lowest branches near the forest floor, the environment no longer provides sufficient cover. Such stands are ideally densely stocked with young pines, but also contain small occasional patches of open areas or with sparse tree cover.
Controversy The status of the overwintering habitat has been contentious, with researchers disagreeing. Mayfield (1992, 1996) first stated that the bird inhabits the shrub layer. Lee et al. (1997) also believed that the warbler inhabits shrubs, but they concluded that the species is entirely dependent on pineyards, stating that before the advent of deforestation of the high coppice after the colonisation of The Bahamas by pre-colonial Lucayan peoples, the bird must have been restricted to the northwestern islands which harbour these pineyards and absent from central, eastern and southern islands such as Eleuthera. Sykes and Clench (1998), basing their analysis on 96 unambiguous records of both collected specimens and observations on thirteen different islands, as well as almost 451 observations over three months of the same two banded individuals on Eleuthera, refuted the claim, finding that by far most records were from regrown coppice after abandonment of agricultural fields. Like Mayfield, they state many of the earlier records used by Lee et al. were tainted by misidentification with S. dominica flavescens, a similar-looking subspecies that was not adequately described or illustrated at the time of the recordings. A few months later, Haney et al. (1998) published a repudiation of Sykes and Clench based on 101 warbler records, wherein they claimed the warblers do not prefer scrub coppice and reiterated their earlier assertion that the primary habitat of the birds was pineyards. They went even further in concluding that the world population of the warbler was not limited by the situation in their breeding range in Michigan, but that historic fluctuations in their population were instead being determined by the status of the pineyards in Bahamas. A detailed study by Wunderle et al. (2010) using a much larger sample size of new data from 153 capture sites and 499 observations, and investigations of the diet, found that Sykes and Clench had been correct, and there was no validity to the assertions of Lee, Walsh-McGehee and Haney. Jones et al. (2013), researching the warbler on an island where pineyards had never grown, hypothesized that a sampling bias for birds in pineyards had skewed the results of the research presented by Haney et al. Despite the evidence, Birdlife International, which performs the IUCN Red List assessments, has consistently shown preference for the Haney et al. interpretation, stating that the conclusion that "changes in population have occurred contemporaneously with the degradation and recovery of the north Bahamas pine ecosystem" is more compelling than that the recovery efforts in Michigan were having effects on the population size.