Unmated males sing more than five times as often as paired males (Gibbs 1988).
New York is the northern-most extent of the Kentucky Warbler range. During the second Breeding Bird Atlas (2000-2005), Kentucky Warblers were reported in 11 blocks, with six probable or confirmed breeding blocks (McGowan and Corwin 2008). In contrast, the first Breeding Bird Atlas (1980-1985) reported Kentucky Warblers in 39 blocks, with 27 probable or confirmed breeding blocks (Andrle and Carroll 1988). When comparing the two breeding bird atlases, it appears the population is declining. Long-term trends indicate that populations fluctuate in the state.
When comparing the two breeding bird atlases, it appears the Kentucky Warbler population may be declining in the state. The first Breeding Bird Atlas (1980-1985) reported Kentucky Warblers in 39 blocks with 27 probable or confirmed breeding blocks (Andrle and Carroll 1988). Kentucky Warblers were reported from 72% fewer blocks during the second Breeding Bird Atlas, with the species reported in 11 blocks of which 6 were probable or confirmed (McGowan and Corwin 2008). The species is reported too infrequently on Breeding Bird Survey routes in New York to determine trends in the state (Sauer et al. 2007). With continued threats to its habitat in New York and its wintering grounds, the future status of this species in New York is not certain with predictions of possible extirpation (McGowan and Corwin 2008).
The peak population may have been in the 1870s when 16 individuals and four nests were found near Ossining in Westchester County (Andrle and Carroll 1988). Breeding was documented in Cortland County in 1903 and 1906 (Levine 1998). Soon after, Kentucky Warblers were absent from the state as a breeder for 30 to 40 years. The disappearance from New York is not understood (Andrle and Carroll 1988). During the 1950s, breeding Kentucky Warblers returned to the state and populations started to increase, but probably were not as high as they were in the late 1800s. This trend continued until the 1980s or 1990s. According to the second Breeding Bird Atlas, it appears that populations are once again declining in New York (McGowan and Corwin 2008).
Forest fragmentation is perhaps the greatest threat to Kentucky Warblers. Southern New York, in particular the Lower Hudson River Valley, is currently under high development pressure. In areas where forests are more fragmented, brood parasitism from Brown-headed Cowbirds increases which can greatly decrease reproductive success. High White-tailed Deer populations may greatly reduce the amount of dense, low vegetation that this species needs during the breeding season. If predator populations (such as raccoons and snakes) are high, there may be an increased risk of nest failure. Threats on the wintering grounds may also be contributing to the decline of this species in the state.
Land managers should promote the growth of dense, low vegetation in the forest understory. Deer management may be needed if deer over-browsing is a problem. Contiguous, moist forests are ideal for Kentucky Warblers to reduce brood parasitism by Brown-headed Cowbirds.
More research is needed to determine reproductive success, the effects of deer over-browsing in New York, and the minimum area required for a breeding pair.
In New York, Kentucky Warblers prefer rich, moist, flat or preferably hilly woodlands especially with stream-bearing ravines and a dense understory. They will breed in forests of various ages but are most common in medium-aged forests (NatureServe 2005). They are seldom found in conifers.
The highest densities of Kentucky Warblers are found in the Lower Hudson River Valley. There are scattered populations in the Coastal Lowlands and even more scattered locations in central and western New York in the Delaware, Susquehanna, and Allegheny River valleys.
Breeding: Kentucky Warblers are found during the breeding season from southeastern Nebraska, east across central Iowa, southwestern Wisconsin, northeastern Illinois, central Indiana, north-central Ohio, southern Pennsylvania, northern New Jersey, and southeastern New York, to southwestern Connecticut, south to Texas, the Gulf Coast to northwestern Florida, central Georgia, and South Carolina, and west to eastern Kansas and central Oklahoma (AOU 1983 cited in NatureServe 2005). Non-breeding: During the non-breeding season Kentucky Warblers are typically found in tropical zones of southern Veracruz and Oaxaca, through Chiapas, the base of the Yucatan Peninsula, primarily on the Caribbean slope of northern Central America, throughout Costa Rica and Panama, and into northern Colombia and northwestern Venezuela (AOU 1983 cited in NatureServe 2005, McDonald 1998 cited in NatureServe 2005). They are uncommon transients through the West Indies; some may overwinter on eastern and southern West Indies islands (McDonald 1998 cited in NatureServe 2005).
Kentucky Warblers can be identified by the broad, black sideburns extending from the eye and bold, yellow "spectacles." The crown is black. Underparts are yellow to olive. They have a short tail and long legs. Sexes are similar. However, the black sideburns and crowns are usually duller in females. Nests are cup-shaped and made of grasses, various plant fibers, and rootlets. Nests are typically built on or near the ground at the base of a tree or shrub and are usually hidden by vegetation (NatureServe 2005). The average egg size is 18.6 x 14.3 mm. Eggs are white or creamy white and are blotched or dotted with grays and browns with concentrations at one end. The shell is smooth and slightly glossy. The Kentucky Warbler song is a series of rolling musical "chuuree" notes repeated about three to eight times. The song is similar to the Carolina Wren, but is lower in pitch and less musical. The call is a low, sharp "chuck." Other calls are used infrequently.
The best time to observe or hear Kentucky Warblers is May through June while the males are defending territories. Kentucky Warblers are secretive birds that are more often heard than seen. They are rarely found before mid-May and after mid-September.
The time of year you would expect to find Kentucky Warbler active and reproducing in New York.
Geothlypis formosa (Wilson, 1811)
American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 p.
American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.
Andrle, Robert F. and Janet R. Carroll, editors. 1988. The atlas of breeding birds in New York State. Cornell University Press. 551 pp.
Bent, A. C. 1953. Life histories of North American wood warblers. U.S. Natl. Mus. Bull. 203. Washington, D.C.
Bull, John. 1974. Birds of New York State. Doubleday, Garden City, New York. 655 pp.
Bushman, E. S., and G. D. Therres. 1988. Habitat management guidelines for forest interior breeding birds of coastal Maryland. Maryland Dept. Natural Resources, Wildlife Tech. Publ. 88-1. 50 pp.
Carter, M., C. Hunter, D. Pashley, and D. Petit. 1998. The Watch List. Bird Conservation, Summer 1998:10.
Carter, M., G. Fenwick, C. Hunter, D. Pashley, D. Petit, J. Price, and J. Trapp. 1996. Watchlist 1996: For the future. Field Notes 50(3):238-240.
DeGaris, C. F. 1936. Notes on six nests of the Kentucky warbler (OPORORNIS FORMOSUS). The Auk 53:418-28.
Droege, S., and J.R. Sauer. 1990. North American Breeding Bird Survey, annual summary, 1989. U.S. Fish and Wildlife Service, Biological Report 90(8). 22 pp.
Gibbs, J. P. 1988. Forest fragmentation, mating success, and the singing behavior of the ovenbird. (SEIURUS AUROCAPILLUS) and Kentucky warbler (OPORORNIS FORMOSUS) in central Missouri. Univerity of Missouri, Columbia, Missouri. Unpublished M.S. thesis.
Gibbs, J. P., and J. Faaborg. 1990. Estimating the viability of ovenbird and Kentucky warbler populations in forest fragments. Conservation Biology 4:193-196.
Griscom, L., and A. Sprunt, Jr. 1979. The warblers of America. Doubleday and Co., Garden City, New York. 302 pp.
Hagan, J. M., III, and D. W. Johnston, editors. 1992. Ecology and conservation of neotropical migrant landbirds. Smithsonian Institution Press, Washington, D.C. xiii + 609 pp.
Harrison, C. 1978. A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Cleveland, Ohio.
Harrison, H. H. 1979. A field guide to western birds' nests. Houghton Mifflin Company, Boston. 279 pp.
Harrison, H.H. 1984. Wood warblers' world. Simon and Schuster, New York. 335 pp.
Keast, A., and E.S. Morton. 1980. Migrant birds in the neotropics: ecology, distribution, and conservation. Smithsonian Institution Press, Washington, DC.
Levine, E. 1998. Bull's birds of New York State. Comstock Publishing Associates, Ithaca, NY.
Mabey, S. E., and E. S. Morton. 1992. Demography and territorial behavior of wintering Kentucky warblers in Panama. Pages 329-336 in B92HAG01NAUS.
McDonald, M.V. 1998. Kentucky Warbler (OPORORNIS FORMOSUS). In A. Poole and F. Gill, editors, The Birds of North America, No. 324. The Birds of North America, Inc., Philadelphia, PA. 20 pp.
McGowan, K.J. and K. Corwin, eds. 2008. The Second Atlas of Breeding Birds in New York State: 2000-2005. Cornell University Press, Ithaca, NY. 688 pp.
McShea, W. J., M. V. McDonald, E. S. Morton, R. Meier, and J. H. Rappole. 1995. Long-term trends in habitat selection by Kentucky warblers. Auk 112:375-381.
NatureServe. 2005. NatureServe Explorer: An online encyclopedia of life [web application]. Version 4.2. NatureServe, Arlington, Virginia. Available http://www.natureserve.org/explorer. (Accessed: January 19, 2005).
New York Natural Heritage Program. 2020. New York Natural Heritage Program Databases. Albany, NY.
Nott, M. Philip. 2000. Identifying management actions on DOD Installations to reverse declines in Neotropical birds. Available from: https://www.denix.osd.mil/denix/Public/ES-Programs/Conservation/Legacy/Neo-Tropical/neotropical.html.
Raffaele, H. A. 1983a. A guide to the birds of Puerto Rico and the Virgin Islands. Fondo Educativo Interamericano, San Juan, Puerto Rico. 255 pp.
Rappole, J. H., and D. W. Warner. 1980. Ecological aspects of migrant bird behavior in Veracruz, Mexico. Pages 353-393 in A. Keast and E.S. Morton, editors. Migrant birds in the neotropics: ecology, distribution, and conservation. Smithsonian Institution Press, Washington, DC.
Ridgely, R. S. and G. Tudor. 1989. The birds of South America. Volume 1. University of Texas Press, Austin, USA. 516 pp.
Sauer, J.R., J.E. Hines, and J. Fallon. 2007. The North American breeding bird survey, results and analysis 1966-2006. Version 10.13.2007. US Geological Survey, Patuxent Wildlife Research Center, Laurel, MD.
Sauer, J.R., and S. Droege. 1992. Geographical patterns in population trends of Neotropical migrants in North America. Pages 26-42 in J.M. Hagan, III, and D.W. Johnston, editors. Ecology and conservation of Neotropical migrant landbirds. Smithsonian Institution Press, Washington, DC.
Stiles, F. G. and A. F. Skutch. 1989. A guide to the birds of Costa Rica. Cornell University Press, Ithaca, New York, USA. 511 pp.
Terres, J. K. 1980. The Audubon Society encyclopedia of North American birds. Alfred A. Knopf, New York.
Wenny, D. G., et al. 1993. Population density, habitat selection and minimum area requirements of three forest-interior warblers in central Missouri. Condor 95:968-979.
This guide was authored by: Hollie Shaw
Information for this guide was last updated on: July 1, 2019
Please cite this page as:
New York Natural Heritage Program. 2020. Online Conservation Guide for Geothlypis formosa. Available from: https://guides.nynhp.org/kentucky-warbler/. Accessed January 28, 2020.