Gadwalls are almost exclusively surface feeders. They tend to feed in
rather shallow marshes having abundant aquatic plant life growing close
to the surface [
6]. They sometimes feed in stubble fields for grain or
in woods for acorns [
19]. They mainly consume leaves and stems of
aquatic plants but also eat insects, mollusks, crustaceans, amphibians,
and fishes [
9,
16,
19]. Aquatic plants commonly eaten by gadwalls include
pondweed (Potamogeton spp.), widgeongrass (Ruppia maritima), saltgrass
(Distichlis spp.), muskgrass (Chara spp.), eelgrass (Zostera marina),
spikerush (Eleocharis spp.), spiked watermilfoil (Myriophyllum spicatum)
and filamentous algae [
9,
16,
19]. The two most prominent plants in the
diet of gadwall in South Carolina are fragrant flatsedge (Cyperus
odoratus) and Carolina redroot (Lachnanthes caroliniana). Major animal
foods include crustaceans, especially those belonging to the order
Anostraca, and insects, especially adult and larval chironomids
(Chironamidae) [
16].
Recently hatched gadwalls in Alberta initially fed on invertebrates but
were essentially herbiverous by 3 weeks of age. Major animal foods of
ducklings included adult and larval chironamids, water boatman
(Cerixidae), beetles (Coleoptera), and cladocerans (Cladocera).
Important plants in the duckling's diets were pondweed, green algae
(Cladophoracea), duckweed (Lemna minor), and seeds of American
sloughgrass (Beckmannia syzigachne) [
16].