Birds feed intensively at a migratory stop-over to build up fat reserves for their next long flight, and this was certainly evident in the ducks I watched at the MN Valley National Wildlife Refuge the other day. Huge rafts of ducks floated far out in the river.
A few smaller flocks of Northern Shoveler were feeding in the shallow marshes near shore and allowed me to creep up closer to photograph them.
Feeding either singly or in small groups, the birds spun in tight circles, keeping their heads and bills immersed in the water and raising up only momentarily (to breathe, I assume).
The effect of the spinning motion, and especially of their feet raking the marsh bottom, brings up all sorts of food items, which are sieved by their grooved ridges (lamellae) along the edges of their elongated bill. Water and food particles are drawn in the tip of the bill and pushed through the lamellae with the tongue to exit at the base of the bill, leaving the residue of food particles to be swallowed. To maximize their contact with the particles suspended in the water, shovelers move the bill from side to side as they sit, spin, and suck in the medium.
Shovelers look a lot like Mallards, with the mottled brown and tan plumage of the hens and the glossy green heads of the drakes.
Not only is the Shoveler bill a lot longer and broader than that of a Mallard, but the specialized lamellae on its edges and the Shoveler’s feeding behavior, mean that the two species have entirely different diets.Northern Shovelers eat a high proportion of animal food (especially snails), in addition to seeds and vegetation that is raked up from the bottom. Mallards eat more plant matter (seeds and vegetation), except during the breeding season, when they too prefer an aquatic animal diet.
The Shovelers will probably leave when the marshy shallows of the lakes and rivers freeze over, and some of them will migrate as far south as northern South America for the winter.