The Common Poorwill, named for its distinctive poor-will call, is the smallest nightjar occurring in North America. This bird is noted for its ability to enter torpor under a variety of conditions. Although probably not a true form of hibernation (Csada & Brigham 1992), poorwills use torpor both in winter and summer as a means of coping with cold and extreme heat. Even incubating adults will occasionally enter torpor. The lowest naturally occurring body temperatures in birds have been recorded in poorwills while in torpor.
Common Poorwills breed primarily in the western half of the United States south into central Mexico, and winter in the southern portion of the breeding range, from the southwestern United States into central Mexico. They are thought to be migratory, although in some areas migration may be altitudinal and not latitudinal (Csada & Brigham 1992). In Texas, migration extends from February through late May (Oberholser 1974); however, they also are early breeders, beginning as early as late March. This overlap in breeding and migration dates may complicate the analysis of TBBAP breeding records. Therefore, atlasers needed to exercise care when assigning breeding status to poorwills from March through May.
DISTRIBUTION: In Texas, the Common Poorwill can be found throughout the western two-thirds of the state. It is usually associated with ground that is bare and rocky with scattered brush. Normally these areas are found in conjunction with slopes, ridges, and canyons, but they may also occur on relatively flat ground, such as in the Rolling Plains and the south Texas brush country.
SEASONAL OCCURRENCE: Breeding of the Common Poorwill is difficult to confirm, with only 4% of the records representing confirmed status (7 records out of 174 total). The easiest way to confirm breeding is the presence of eggs. Poorwill eggs, as are those of all members of this family, are whitish and stand out somewhat from the nesting substrate. Four of the confirmed records were for “nests with eggs”, with dates of 5 April, 13 April, 27 April and 2 June. However, finding a clutch of eggs is difficult due to the poorwill’s cryptic plumage, nocturnal behavior, and reluctance to flush while incubating. Poorwills are most easily found by their vocal activity. Over 58% of the records represent some form of vocal activity.
BREEDING HABITAT: Common Poorwills nest in open, relatively arid areas with some bare ground, rocks, and grass or scattered shrubs. Rarely, they will use growths of low forests (Bent 1940). Commonly, preferred nesting habitat occurs along canyons, slopes, cliffs, mesas and stony hills, and mountains. The two eggs are often laid on bare ground, gravel, or a flat rock; however, they sometimes are laid on dead leaves or pine needles (Bent 1940, Csada & Brigham 1992). No nest is actually built, but a slight depression may be used (Oberholser 1974). The eggs may be laid in full sunlight, but are commonly shaded by small bushes, clumps of grass, or even overhanging rocks (Csada & Brigham 1992). Poorwills aredouble-brooded (Csada & Brigham 1992), but no TBBAP confirmed records appear to represent a second brood.
STATUS: The status of the Common Poorwill in Texas seems to be improving. In the Panhandle and along the Caprock Escarpment, the poorwill may be either more widespread than previously thought or it may be expanding its range. Oberholser (1974) does not show breeding records for the Panhandle, while the T. O. S. Checklist (Texas Ornithological Society 1994) lists the poorwill as uncommon in Palo Duro Canyon (34101) and locally uncommon in Potter County (35101). TBBAP records show the poorwill to be more widespread in the Panhandle, largely in the eastern portions and north of Palo Duro Canyon. Although poorwills migrate through the Panhandle, these records, occurring between 5 June and 24 July, are well past the extreme migration date of late May (Oberholser 1974) and do not appear to be of migrants.
Along the Caprock Escarpment (33101 and 32101), the situation is similar to that in the rest of the Panhandle. Oberholser (1974) and the T.O.S. Checklist (1994) do not show breeding poorwills along the escarpment. The three TBBAP records are probably not migrants, with dates ranging from 8 June to 4 July, again past the extreme migration date. Local checklists tend to support a recent change in poorwills along the escarpment. For example, the Llano Estacado Audubon Society did not list the bird as occurring in summer in their 1976 checklist (Llano Estacado Audubon Society 1976), but listed the bird as rare in summer two years later (Llano Estacado Audubon Society 1978).
Caution should be exercised when interpreting these possible range extensions. Due to the poorwill’s nocturnal behavior, cryptic plumage, tendency for populations to be localized (Csada & Brigham 1992), and greater vocal activity during brighter phases of the moon (Freemyer 1993), these records may simply represent the detection of established breeding populations and not a real range extension. However, these TBBAP records, when combined with new breeding records in the northeastern part of the range (as summarized in Csada & Brigham 1992), show that the bird may indeed be expanding its range. Breeding Bird Survey data (Sauer et al. 1995) show a significant increase in poorwills in Texas since 1966, supporting the possibility of a range expansion. Rangewide BBS data also show a slight, but not statistically significant, increase.
Text by Cade L. Coldren (ca. 1996)
Bent, A. C. 1940. Life histories of North American cuckoos, goatsuckers, hummingbirds, and their allies. U.S. Nat. Mus. Bull. No. 176.
Csada, R. D., and R. M. Brigham. 1992. Common Poorwill (Phalaenoptilus nuttalli). In The birds of North America, No. 32. (A. Poole, P. Stettenheim, and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA.
Freemyer, H. 1993. Call-counts of west Texas Common Poorwills. Bull. Texas Ornithol. Soc. 26: 15-18.
Llano Estacado Audubon Society, compilers. 1976. A birder’s checklist of the Texas South Plains.
Llano Estacado Audubon Society, compilers. 1978. Birds of the Texas South Plains. Llano Estacado Aud. Soc., Lubbock, TX.
Oberholser, H. C. 1974. The bird life of Texas. University of Texas Press, Austin.
Sauer, J. R., B. G. Peterjohn, S. Schwartz, and J. E. Hines. 1995. The North American Breeding Bird Survey Home Page. Version 95.1. Patuxent Wildlife Research Center, Laurel, MD.
Texas Ornithological Society. 1995. Checklist of the birds of Texas, 3rd ed.