Morphometric features of Pacific and American Golden-Plovers with comments on field identification

We measured linear dimensions and evaluated identification criteria in Pacific and American Golden-Plovers (Pluvialisfidva and P. dominica) captured for banding. Most of thefidva sampled were wintering birds in Hawaii, representative ofthe mid-Pacific flyway; additionalfidva nd all dominica were from breeding rounds on the Seward Peninsula, Alaska. The sexes were monomorphic in dominica, and for all practical purposes infidva as well. On average,fulva females had shorter head, bill, and tarsus lengths than males, but at a scale of <1.0 mm for each dimension. Interspecific omparisons howed longest wings in dominica, longest bills and tarsi infidva, and no difference in head lengths. Unpublished ata provided by colleagues tudying plovers in Siberia and Canada enabled us to compare our Alaska findings with breeding grounds elsewhere. There appears to be little, if any, variation infidva wing lengths from the eastern end (Seward Peninsula) to near the western end of the breeding range (Taimyr Peninsula); however, other linear dimensions decreased from east to west. American Golden-Plovers breeding on the Seward Peninsula (western end of their range) had shorter wings and tarsi, but longer bills than birds nesting at the opposite end of the range near Churchill, Manitoba. We found most field identification criteria described in the literature to be less than satisfactory because of variability and overlap between the two species. The only reliable characteristics were breeding plumage, number of primaries exposed beyond the longest ertials (2-3 infidva, 4-5 in dominica), and primary projection past the end of the tail (estimated at 0-9 mm infidva, 12-22 mm in dominica). In field situations involving moulting birds and birds in non-breeding plumage, unequivocal species identification may be impossible in some cases