Influences of age, body condition, and structural size on mate selection by dabbling ducks

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Abstract
Both members of pairs of mallards (Anas platyrhynchos), northern pintails (Anas acuta), northern shovelers (Anas clypeata), and American wigeon (Anas americana) were collected early in the pairing periods in fall and during spring migration (several months after most birds were paired) to provide insights into whether (i) assortative mating occurs; (ii) body condition changes synchronously among pair members; and (iii) characteristics of selected individuals ultimately confer advantages in survival and recruitment. Both members in 19 of 21 mallard, 16 of 16 pintail, 14 of 14 shoveler, and 14 of 15 wigeon pairs were adults. The predominance of adults in pairs in fall indicates that adults pair earlier than juveniles and suggests at least some assortative mating in relation to age. Generally, body and nutrient reserve masses of males and females within a pair were correlated for all species in both fall and spring, suggesting that individuals tend to form pairs with others of relatively similar body condition, and also that once paired, the body condition of the two members tends to change at the same time. In contrast to body condition, measures of structural size of pair members were not correlated. Field data suggest that older and heavier ducks have greater survival and reproductive potential than young, lighter ducks; consequently, selection of old and heavy mates is probably evolutionarily advantageous.