It has been suggested that pairing behavior during winter in migratory ducks represents a trade-off between costs (defense of the female) and benefits (early access to females). To investigate the benefits and costs for both sexes in wintering pairs of ruddy shelducks (Tadorna ferruginea), we compared time budgets for paired males and females, and surveyed the sex ratio of the birds wintering at Lashihai Lake, southwest China. The behavior of the paired ruddy shelducks was monitored for 5 activity types: feeding, resting (including sleeping), preening, drinking and warning. Feeding was the most dominant activity. The feeding time of both sexes increased as the winter season progressed. However, the paired females always spent significantly more time feeding and less time warning than the paired males. Paired ruddy shelducks had access to better feeding grounds than unpaired individuals, resulting in a food benefit for paired individuals over single individuals. Because the sex ratio of the wintering population was strongly male biased (M:F = 1.44:1.00), the paired male also gained the benefit of accessing a female in advance of the breeding season.