Dendroica graciae
Grace’s Warbler is one of the most poorly known warblers breeding regularly in the United States, although it is not hard for birdwatchers to add to their life-lists. The inaccessibility of its nests and foraging areas high in ponderosa pine trees makes study of its breeding season ecology difficult. In Texas the species is limited by the scarcity of breeding habitat available to it.
DISTRIBUTION. TBBA volunteers found confirmed breeding evidence for Grace’s Warbler in the Guadalupe Mountains, (where Oberholser [974] reported nests were found) and also in the Davis Mountains, where no previous breeding evidence had been obtained, although this species had been found there before.
In other states and countries, Grace’s Warbler breeds from southern Nevada, southern Utah and southwestern Colorado, south through Arizona, New Mexico and the mountains of western Mexico to the Isthmus of Tehuantepec and the highlands of Chiapas, Mexico. The species also breeds in the highlands of Guatemala, Belize, Honduras, and Nicaragua, and in coastal areas of eastern Honduras and northeast Nicaragua. After breeding northern populations move south to Mexico for the winter (Stacier and Guzy 2002).
SEASONAL OCCURRENCE. Grace’s Warblers arrive in Texas from April 21 to June 1, and probably breed from mid-May to mid-August before departing for the wintering area between August 8 and September 24 (Oberholser 1974).
BREEDING HABITAT. Grace’s Warbler nests located in the Guadalupe Mountains were at an elevation of about 2100 m (7000 ft) in pine-oak forests of the Transition Zone. The nest is built on a horizontal pine tree limb, up to 18 m (60 ft) above the ground and often hidden in a clump of needles. It is a compact cup built of plant fibers such as catkins, bud scales from oaks, hair, plant down, spider webs and occasionally string or straw. The nest is lined with dry grasses, hair and feathers. The outside diameter is 8 cm (3 in), height 4 cm (1.5 in), inside diameter 4.5 cm (1.8 in) and cup depth 3 cm (1.3 in)
The female lays 3, occasionally 4, creamy white eggs and incubates them for at least 10-12 days. Both parents gather food, for the nestlings, but the female feeds and broods them. The nestling period is unknown. Grace’s Warblers are parasitized by Brown-headed Cowbirds (Molothrus ater), heavily in some places (Oberholser 1974, Harrison 1979, Stacier and Guzy 2002).
STATUS. Lockwood and Freeman (2004) report Grace’s Warbler as an uncommon to very locally common summer resident in the Guadalupe and Davis mountains.
The Breeding Bird Survey (BBS) does not sample Grace’s Warbler in Texas because of the inaccessible (by road) locations of its breeding areas. Nationwide only 39 routes have detected this species, producing a 95% confidence interval of -6.2 to 1.3% population change per year for the period 1966-2004 (Sauer et al. 2005).
The stability of any breeding population as small as that of Grace’s Warbler in Texas is always precarious, and Lockwood and Freeman’s (2004) report that this species is rarely recorded in migration is not reassuring for the future of this species in Texas. Text by Robert C. Tweit (2005)
Literature cited.
Harrison, H. H. 1979. A field guide to western birds’ nests. Houghton Mifflin, Boston, MA.
Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.
Oberholser, H. C. 1974. The bird life of Texas. Vol. 2. University of Texas Press, Austin.
Sauer, J. R., J. E. Hines, and J. Fallon. 2005. The North American Breeding Bird Survey, results and analysis 1966-2004. Version 2005.1. USGS Patuxent Wildlife Research Center, Laurel MD (Web site, http://www.mbr-pwrc.usgs.gov/bbs).
Stacier, C. J. and M. J. Guzy. 2002. Grace’s Warbler (Dendroica graciae). In The birds of North America, No. 677 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.