The population of the American black duck (Anas rupripes) has declined dramatically in recent decades whereas mallards (Anas platyrhynchos) and wood ducks (Aix sponsa) have increased.
This decline has been attributed to many factors including overharvest, introgressive hybridization by mallards, competitive superiority of mallards, and habitat degradation.
Alternatively, it is possible that the different kinds of ducks are more sensitive to human disturbance in their habitat, displaying greater levels of neophobia (fear of "new" things) and/or wariness towards humans.
In January 2005, Russell Greenberg, ornithologist at the Smithsonian Migratory Bird Center, tested the degree of neophobia in wild populations of black ducks, mallards, and wood ducks by measuring their latency to feed near familiar and novel objects at the ponds by the Bird House at the National Zoo.
Below are two video clips showing the experiments in action (clips may take a few seconds to load).
The first shows a "control" experiment, one where there is no "novel" object.A pile of duck food has been placed on an island in the duck pond.
Initially, the ducks are hesitant but they approach the food fairly quickly and once the first birds begin eating, there is a mad rush of waterfowl to devour the remaining duck food.
Control experiment, no novel object
In the second video clip a series of "novel" objects, plastic orange cones, have been placed to surround the duck food.
The ducks take much longer to walk onto the island (not shown in video) and although they are quite aware of the food, they will not pass the cones. Notice how they circle around the cones hoping to find a clear path to the food.
Experiment with novel objects
After 30 minutes, the ducks never did feed. During experiments on subsequent days, using the same novel object, the ducks finally overcame their fear and fed.
Additional experiments using other "novel" objects (e.g. foil-wrapped softballs) are continuing. By analyzing which kinds of duck feed first, and how long it takes them to feed, it is hoped that we will gain a better understanding of the impacts humans have on wild populations of ducks.