The black-capped vireo breeds in a relatively narrow area of the south-central United States and north-central Mexico. It was likely extirpated from Kansas by the 1930’s and is now gravely endangered in Oklahoma and much of the northern, eastern, and central portions of its range in Texas. Among the most influential factors contributing to its decline are: nest parasitism by the brown-headed cowbird, habitat deterioration through destruction, and natural successional changes resulting from fire suppression.
The black-capped vireo has been designated an endangered species by the U.S. Fish and Wildlife Service, and is a major component of wildlife management interests on the Wichita Mountains Wildlife Refuge. Unlike other vireos, this species shows distinct plumage differences in cap color between the sexes. In addition, males exhibit delayed-plumage maturation (first-year males have gray napes). During the breeding season, male black-capped vireos sing persistently well into the heat of the day, the intensity of their singing seeming to increase after singing by other local species has waned.
This species’ songs with alternating phrases are typical of those of many other vireo species, but they are unusual in being derived from a large syllable repertoire, an order of magnitude greater than that of other vireos. (Excerpts from the Birds of North America, No. 181, 1995).
Standardized survey areas for the black-capped vireo territories run this year between May 5th and June 19th. The eleven standardized search areas established last year, included portions of the core colony, the primary satellite colonies, and new expansion areas. A total of 914 territories were identified.Vireos were most often detected from vocalizations of males. Taped songs were replayed at times in areas where no vireos had yet been heard to stimulate response of males potentially present. Surveys generally began no earlier than 2 hour after sunrise and could be conducted until approximately mid-afternoon. Because of the persistent song patterns of vireos, males can routinely be detected within this time. Where vireo territories were adjacent to each other, detections would only be counted as separate from others if an adjacent male could be heard simultaneously or was substantially separated from other detections.Because of the rate of travel of the observer, and previously estimated detection probabilities, the number of territories mapped is expected to represent about 85% of the total males present in the search areas. Because about 88-90% of the males are mated, the number of territories detected through this survey process can be utilized as a conservative estimate of the number of pairs present within the search areas.
The 2005 Black-capped vireo population is in excess of 1250 birds. This represents a realistic minimum population Refuge wide, as there are more than 8,000 acres of suitable habitat that is not within the standardized areas sampled. Fort Sill, adjacent to the Refuge, also has suitable habitat and an expanding vireo population. This year, in excess of 500 birds were located on the Fort. A true endangered species success story. |
