7q.0Q 1 Vol. 79, pp. 1-12 23 May 1966 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON GEOGRAPHIC VARIATION IN AZARA'S MARSH BLACKBIRD, AGEhAlVb CYANOPUS By Kenneth C. Pakkes Carnegie Museum, Pittsburgh, Pennsylvania Of the well-known and widely distributed icterid genus Agelaius, perhaps the least studied species has been Azara's Marsh Blackbird, A. cyanopus Vieillot, of Argentina, Paraguay, Bolivia and Brazil. It has been universally treated as a mono-typic species. This is understandable in view of its general rarity in collections; those few institutions fortunate enough to possess specimens of Agelaius cyanopus from more than one population seldom, if ever, have series comparable as to age and sex. To complicate matters further, there is no detectable geographic variation in definitively plumaged males other than in size; all are simply black. The realization that three specimens in Carnegie Museum, long generically misident-ified, actually represented an isolated and strikingly dif-ferent population of Agelaius cyanopus led to a study of this species based on material assembled from several mu-seums. It quickly became apparent that A. cyanopus, like most of its congeners, is most emphatically a polytypic species, with no less than four morphologically distinct and geograph-ically isolated populations. Of the three outlying populations, a total of only 22 specimens could be assembled; over twice this number of the nominate race were examined. All measurements in this paper are in mm. The wing was measured flattened against the ruler. The tail measurement is the standard one for birds, and the bill measurement is that of the total length of the culmen from the base. Acknowledgments: In addition to specimens in the Carnegie Museum, material from the following museums was examined ( abbreviations used later in the paper are noted ) : Academy of Natural Sciences of Philadelphia (ANSP), American Mu-1— Proc. Biol. Soc. Wash., Vol. 79, 1966 (1) 1»r: MAY 2 3 1966 nsriioTiON
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