Disparate sex ratios in waterfowl are considered indicative of differential survival between the sexes and may limit reproductive potential. Because other studies have shown canvasbacks (Aythya valisineria) have highly skewed sex ratios, I examined aerial photographs from surveys flown monthly during winters 1987-88 and 1988-89 to determine sex ratios of canvasbacks in Louisiana where the wintering population is increasing. Estimated statewide sex ratios (proportion male) were balanced during the initial arrival period in November (1987: 0.505, 1988: 0.524), dominated by males during December-February (range = 0.600- 0.655), and then dominated by females as birds departed in March (1989: 0.419). Sex ratios varied geograph- ically with males being more prevalent in flocks at inland sites than in coastal areas. Canvasback sex ratios did not vary by flock size nor between major- and minor-use areas. Canvasback sex ratios in Louisiana appeared to be representative of the population wintering in the lower Mississippi Valley and Gulf Coast region and were less male dominated than the sex ratios projected for the population wintering in the Atlantic Flyway. Overall sex ratio characteristics imply that female canvasbacks in Louisiana may have higher annual survival or recruitment rates relative to males than occur in other wintering populations. I suggest that this may partially explain the observed increases in canvasbacks wintering in Louisiana.
