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Kentucky Warbler

KENTUCKY WARBLER

Photo Credit: U. S. Fish and Wildlife Service

SCIENTIFIC NAME: Oporonis formosus (Wilson)

OTHER NAMES: None.

DESCRIPTION: Sparrow-sized (13 cm [5 in.]), relatively slow-moving, large-billed insectivore of forest understory. Underparts boldly and beautifully colored with brilliant yellow; upperparts a dirty green. Most distinctive feature is a striking yellow spectacle that curls between a black/gray cap and a black crescent running below the eye and around the edge of throat. Relative proportion of black and gray feathers in cap variable, with males being blacker than females, and old males being blacker than young males. Legs are pink. Females marked like males, but with more subdued colors. Loud, rolling song is composed of two-syllable notes repeated three to eight times and sounds like chuuree-chuurree-chuuree. In addition, a loud distinct chip call is given by both sexes. No subspecies recognized (McDonald 1998).

DISTRIBUTION: Breeds virtually throughout the eastern United States extending north to Wisconsin, Michigan, and New York and west to Texas, Oklahoma, and the edge of Nebraska (McDonald 1998). Absent as breeders from the Florida peninsula. Based on Breeding Bird Survey data, its centers of abundance are the Ohio River Valley and the south-central United States including Arkansas, Louisiana, and Mississippi (Sauer et al. 2001). Winters in Central America from the Atlantic states of Mexico to Panama (McDonald 1998).

HABITAT: Requires relatively large patches of forest. In Missouri, at least 500 hectares [1,235 acres] of continuous habitat required for successful breeding (Gibbs and Faaborg 1990). Prefer mature bottomland hardwoods with an open midstory and dense understory (McDonald 1998). Not generally found in dense young riparian stands, and generally absent from dry oak-hickory-pine forests. However, in Bankhead National Forest, Alabama, common in upland, 20-year-old loblolly pine stands that support a dense layer of tulip poplar-sweetgum 0.5 to 1.5 meters (1.5-4.5 feet) high (Hill 1997). Thus, some silviculture lands can potentially provide suitable breeding habitat if stands are thinned, midstory cover is reduced, and dense ground cover of shrub/tree sprouts is encouraged. Soil moisture will likely dictate whether pine plantation lands have potential to support breeding Kentucky warblers, with the ability to develop a densely vegetated groundcover the key determining factor.

LIFE HISTORY AND ECOLOGY: Males arrive in mid- to late April in Alabama and immediately establish territories that they defend vigorously from other males. During this period, males sing regularly through day. Females arrive shortly after males and form pair bonds. Socially monogamous; only one female associates with one territorial male during a nesting effort. However, females often switch mates after a nesting failure within a breeding season, and males and females virtually never pair together for more than one breeding season. Moreover, about half of all nests have young fathered by a male other than social mate of female (McDonald 1998). Female builds a well concealed simple cup nest on the ground in dense vegetation. Typically four (range three to six) dirty white eggs laid and incubated by female for 11 to 13 days. Only females brood, but both parents feed young. Nestling period eight to nine days and young may remain with parents for about a month. At fledging, brood typically divided between sexes who move apart to care for young. Occasionally, two broods raised (McDonald 1998). Fall migration begins with first birds departing in late August, but most birds move south in September and October. For both southern and northern migration, most birds fly over Gulf of Mexico. On wintering grounds, establish individual territories from which they exclude all Kentucky warblers. Interestingly, despite this territorial behavior, neither males nor females sing during winter. In breeding and wintering habitats, feed on ground by searching as they walk and by turning leaves with bills and scratching at leaf litter with feet. Feed primarily on arthropods.

BASIS FOR STATUS CLASSIFICATION: In Alabama, declined steadily in abundance over the last four decades (Sauer et al. 2001). Remains a relatively common and widespread bird, but exists in increasingly localized populations and virtually entire habitat in the state remains at risk for development or timber extraction. If the present decline continues, species will certainly rise in priority ranking and possibly receive higher status designation. Priority designation in Alabama based on Partners In Flight (PIF) data indicating low relative abundance, limited wintering distribution, and significantly decreasing population trend (PIF 2002).

Author: Geoffrey E. Hill


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