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 More than 1 million ducks stop each spring in the backwater lakes
and shallow wetlands of the Illinois River, dining on annual grass
seeds, underwater vegetation, and waste grain in crop fields.
Spring is important for duck populations because it precedes the
breeding season. Healthy ducks in good condition typically have more
ducklings with higher survival rates. Thus, more food in the spring
can help ensure more abundant duck populations in the fall.
In 2010 and 2011, researchers studied ducks’ eating habits by
identifying the amount of seed left over in artificial foraging
patches and using computer models to consider various factors, such
as predator risks, seed depth in sediment, and seed size.
“We want to know how many acres of wetlands to protect and restore
for waterfowl populations for spring and fall flights,” said Heath
Hagy, director of the Forbes Biological Station at the Illinois
Natural History Survey (INHS), a division of PRI. “To do this, we
use energetic carrying capacity models. One aspect of this model is
the giving-up density, or the point at which ducks stop foraging and
move on to another patch.”
Hagy likened this term to a serving pan of cold, soggy macaroni and
cheese that is left at the buffet after diners have filled their
plates and their stomachs. If this unpalatable food is not
discounted, there is a tendency to overestimate the amount of food
that is available.
Hagy and colleagues buried 34 round dog food bowls filled with rice
and millet seeds underwater in locations throughout the central
Illinois River Valley, and they later sorted seeds to figure out how
much food the ducks left behind. They also tested effects of habitat
characteristics on food use. For example, they erected a barrier to
block the ducks’ surrounding view of the area, increasing the ducks’
perceived risk from predators.
“There
was a small effect of predation risk on movement away from the
feeding patch when food was plentiful, but it is perhaps more
interesting that there was no effect of predation risk when food was
limited.”
Hagy said.
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During the
year with abundant rain, food was plentiful, and ducks could be
picky about the food they chose. During the drier year, however,
more food was consumed per plot because ducks had fewer dining
choices.
Studies of this kind help land managers predict how many acres of
wetlands are needed to sustain duck populations. A healthy
population is important for the recreational waterfowl hunting
industry, which provides $453 to the Illinois economy for each bird
harvested, according to an INHS survey.
This study has been published in the Journal of Avian Biology,
and was funded by the U.S. Fish and Wildlife Service.
About the Prairie
Research Institute:
The Prairie Research Institute (PRI) at the University of Illinois
at Urbana-Champaign comprises the Illinois Natural History Survey,
Illinois State Archaeological Survey, Illinois State Geological
Survey, Illinois State Water Survey, and Illinois Sustainable
Technology Center. PRI provides objective natural and cultural
resource expertise, data, research, service, and solutions for
decision making, the stewardship of Illinois’ resources, and the
public good.
www.prairie.illinois.edu
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