THE TAXONOMY OF ROUGH-WINGED SWALLOWS (STELGIDOPTERYX; HIRUNDINIDAE)IN SOUTHERN CENTRAL AMERICA F. GARY STILES Escuelade Biologicl, Universidad de Costa Rica, Ciudad Universitaria, Costa Rica ABSTRACT.--Based on morphological and distributional information, it appearsthat two species of Stelgidopteryx swallows breed in Costa Rica: the northern and highland serripennis (repre- sentedby the racefulvipennis, if one recognizes subspecies at all), and the southern and lowland ruficollis (represented by uropygialis on the Caribbean versant and decolor on the Pacific). In general, the forms of ruficollis have larger bills, shorterwings, brighter throats, and paler rumps than do those of serripennis. Overlap without demonstrable hybridization occurs between uro- pygialis and fulvipennis locally along the northern and easternfoothills of the central highlands of Costa Rica. Previousaccounts of hybrids, intergrades, etc. have failed to take into account the amount of individual variation and migratory behavior of all forms. Appropriate English vernac- ulars for the speciesserripennis and ruficollis would be Northern and Southern Rough-winged Swallow, respectively. Received 10 June 1980, accepted 24 September1980. THE Rough-winged Swallows of the genusStelgidopteryx are fairly small (ca. 15 g), brownish swallows, adult males of which possess short, stiffened barbs with sharp recurved tips on the outer web of the outermost primary; these produce the "rough" or "saw-toothed" feel to the leading edge of the wing that gives the birds their English and Latin names. Virtually all recent systematic discussions (e.g. A.O.U. 1957, Mayr and Short 1970)consider the genus monotypic, the singlespecies S. ruficollis being divided into numerous races distributed from southern Canada to Argentina. In the past, however, two to four species were often recognized (e.g. Ridgway 1904). The presence of two of these forms in Costa Rica, apparently breed- ing sympatrically (Skutch 1960 and pers. comm.) prompted me to reexamine the relationships of these birds. In the process, I have examined virtually all specimens of Stelgidopteryxfrom southern Middle America in major museums and investigated breeding distributions in the field. The major conclusion to emerge is that there do appear to be two species of Rough-winged Swallows breeding in Costa Rica, with only slight geographical overlap and no conclusive evidence of hybridization. HISTORICAL REVIEW Most of the forms of Stelgidopteryx discussed here were described within a short period: the North American breedingrace serripennisfrom South Carolina by Au- dubon in 1838, the southern Mexico-northern Middle American fulvipennis from Jalapa, Veracruz by Sclater in 1859, and the southern Middle American-northern South American uropygialis from central Panam& by Lawrence in 1863 (original citations in Ridgway 1904). The fact that the original descriptionoffulvipennis was basedon a juvenal bird led to confusion:in 1904 Ridgway (1904) named what turned out to be the adult of this form as a new species, salvini (type locality Duefias, in the central Guatemalan highlands),and in the process synonymizedfulvipennis with serripennis. Ridgway considered "salvini" closestto serripennis (but distinct) and considered uropygialis to be a representative of the South American S. ruficollis complex. He distinguished "salvini" from serripennis on the basis of its darker crown, brighter throat (these characters showing some approach to the condition in 282 The Auk 98: 282-293. April 1981