Diet of Lesser Scaup Wintering on Lake Pontchartrain, Louisiana

Abstract

The 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.

Variation in the Diet of Ducks During Spring Migration

“…Winter diet of scaup appears to be more carnivorous than most other species of ducks, but similar to fall, varying considerably by location. Previous researchers reported scaup to consume of 81% plant material during winter on the Detroit River, 0–49% plant material in Louisiana, 12% plant material in South Carolina, and 15–17% plant material in Arkansas, USA, fish ponds (Drobney and Jones 1986, Hoppe et al 1986, Afton et al 1991, Stroud et al 2019, Clements et al 2020). Drobney and Jones (1986), however, reported 43% of the diet (>50% of plant material consumed) of scaup wintering on the Detroit River was unidentifiable plant parts (i.e., stems, detritus) that have little if any nutritional value and suggested the 81% plant material estimated from the study may be inflated by incidental consumption of plant parts while foraging for invertebrates.…”

Scaup Depredation on Arkansas Baitfish and Sportfish Aquaculture

“…Scaup diets consist of a diversity of both plant and animal organisms depending on location within their range and time of year (Bartonek and Hickey 1969, Dirschl 1969, Ross et al 2005, Badzinski and Petrie 2006, Anteau and Afton 2008. Diets of scaup collected at southern latitudes of the United States tend to be composed primarily of animal organisms from classes Bivalvia, Gastropoda, and Insecta (Hoppe et al 1986, Wooten and Werner 2004, Stroud et al 2019.…”

“…Rogers and Korschgen (1966) collected 37 scaup from two locations in Lousiana and found that collectively 46% (n = 17) of the scaup contained fish fragments or sheepshead minnows (Cyprinodon variegatus), which represented 42% of their diet by volume. Other examples of fish consumption by scaup occurred on ponds used for commercial baitfish production in Arkansas (Philipp andHoy 1997, Wooten andWerner 2004) that presumably have much higher densities of fish than natural wetland and lake habitats where scaup have often been collected for diet analysis , Stroud et al 2019. collected scaup from Rockefeller Wildlife Refuge and found that fish represented <0.05% of lesser scaup diets during midwinter migration in southwestern Louisiana.…”