Pair formation in ducks is thought to be influenced by the acquisition of breeding plumage, the occurrence of courtship display, or both. We examined the frequency of pair formation in Mallard (Anas platyrhynchos), Green-winged Teal (Anas crecca carolinensis), and Northern Shoveler (Spatula clypeata) in the central valley of California in relation to the frequencies of male attainment of breeding plumage and courtship display. Predictions related to two hypotheses are: (1) the timing of pair formation is directly related to the attainment of breeding (definitive alternate) plumage by males, and (2) frequencies of courtship display are highest during pair formation. Most female Mallard were paired by the end of October, with >80% in pairs by early December. Of Northern Shoveler, 90% were paired by early January and 90% of female Green-winged Teal were paired by early February. The highest rates of courtship display by Mallard were observed during October through November, by Northern Shoveler in November, and by Green-winged Teal in November through January. Courtship display was, therefore, relatively frequent at the same time as pair formation for all three species. Northern Shoveler spent less time in courtship display than the other two species. Most (90%) male Mallard had acquired alternate plumage by mid-November, Northern Shoveler by early February, and Green-winged Teal by mid-December. Thus, timing of pair formation coincided with timing of attainment of breeding plumage in Mallard and Green-winged Teal but not Northern Shoveler.
