Swirling Shovelers

Last month, I explained how to ID a Northern Shoveler. This time, I thought I would write more about their ducky lifestyles.

Northern Shoveler_RMANWR-CO_LAH_8467

Northern Shovelers are common ducks, inhabiting shallow lakes, mud-bottomed ponds, and marshes. They’re found around the world, in both the eastern and western hemispheres. While they breed in the north, winter vagrants have been discovered as far south as Australia and South Africa. And, with their distinctive bill, they’re one of the easiest birds to recognize. Maybe because they take so little effort to find, and they’re so readily identifiable, I have always quickly checked shovelers off my list, then moved on to more “interesting” species. But on a recent birding trip to a wildlife refuge just north of Denver, I finally appreciated how fascinating Northern Shovelers are.

What first caught my attention that day was their sheer numbers. The small lake was covered with hundreds of shovelers. What kept my attention was the realization that they weren’t just randomly paddling about. Rather, they were swimming in circles, with perhaps 20 ducks per rotating “raft.” I’d never seen this behavior before, and I assumed it had something to do with how they eat. I was right.

Northern Shoveler_BosquedelApacheNWR-NM_LAH_9178Most dabbling ducks turn bottoms up, munching on plants and invertebrates on the bottom of shallow ponds. Shovelers do this, as you can see, but they were more likely to be swimming so that their wide bills skimmed just under the surface. I learned that the bills have comb-like edges (called lamellae) that function much like the baleen of whales—as they turn their heads from side to side, the ducks suck water in the front of their bills, then squirt it out the sides. In the process they strain out insects, crustaceans, and snails, along with bits of grasses, duckweed, and other aquatic plants. It turns out that all duck bills have lamellae, but in the case of shovelers they’re particularly well developed. That explains why they were swimming with just their bills submerged—but why the swirling?

Northern Shoveler_RMANWR-CO_LAH_8468

Paddling in a large circle creates an eddy that brings food to the surface, where the ducks can eat it. It must work well—Wilson’s Phalaropes do the same thing, and for the same reason. In their case, however, they tend to spin solo, rather than gathering in groups like the shovelers.

With my interest piqued, I read further. It turns out that the males put a lot of energy into pursuing the females, who often have a bevy of suitors. According to the Cornell Lab of Ornithology, however, the pairs are monogamous once she declares a winner. After mating, it’s the female who does all the work, building a ground-level nest hidden in a grassy field, away from the water, laying approximately a dozen eggs, then single-handedly rearing the ducklings. Cornell’s website offered another interesting factoid: “When flushed off the nest, a female Northern Shoveler often defecates on its eggs, apparently to deter predators.” Ewww!

Northern Shoveler_BearLakeMigratoryBirdRefuge-UT_LAH_3612

Most of the range maps I discovered showed shovelers wintering south of Colorado, but here was abundant proof that these ducks are happy even north of Denver, as long as they have open water to provide shelter and a food source. This discovery simply proves that ducks don’t read field guides!

 

 

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