Diet of Lesser Scaup Wintering on Lake Pontchartrain, Louisiana

Abstract

AbstractThe lesser scaup Aythya affinis has been a species of conservation concern since continental breeding populations began declining in the 1980s. The causes of this decline are likely multifaceted, but cross-seasonal effects are believed to play a prominent role: females unable to acquire sufficient nutrient reserves during winter and spring migration have poor survival and breeding success. Understanding scaup diet composition and prey selection can help managers not only diagnose mechanisms underlying wintering scaup distributions, but may also help direct management actions to increase forage availability and quality. We evaluated the diet of 60 scaup collected from a major wintering site in Louisiana, Lake Pontchartrain. Scaup consumed almost entirely mollusks, especially targeting medium-sized (6–16 mm) common rangia clams Rangia cuneata, which were strongly selected relative to their availability. Eighty-two percent of scaup consumed dark false mussels Mytilopsis leucophaeata and 57% consumed dwarf surf clams Mulinia lateralis; both foods were selected by scaup, but were uncommon in benthic samples. On the other hand, small snails Texadina sphinctostoma, Probythinella protera were common in dredge samples but were either avoided or consumed in proportion to their availability. We conclude that medium-sized common rangia clams and dark false mussels are the most consumed foods for scaup wintering on Lake Pontchartrain, and hypothesize that annual variation in prey populations may be an important proximate driver of scaup abundance.