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JF Griffin - Index

JF Griffin - magazine - Index

Tina Yerkes, Ducks Unlimited
Building a Bioenergetic Model to
Assess Carrying Capacity
In order to set appropriate
population and harvest goals for black
ducks, biologists need to understand
their energetic requirements as well as
the carrying capacity of the habitat. To
accomplish this, researchers construct
cape May national Wildlife Refuge manager Howard
schlegel releases a satellite-radioed black duck.
a bioenergetic model by answering
three energetic questions:
1) How much energy do wintering
black ducks need?
2) What foods do black ducks
consume?
3) How much energy is available to
wintering black ducks in terms of
food items on the marsh?
To shed light on these questions,
researchers collect data necessary
to assemble time-energy budgets.
First, flocks of ducks are surveyed
to determine the percentage of birds
engaged in nine predefined activities:
feeding, loafing, sleeping, comfort
(preening and wing stretching),
agonistic (bothering other ducks),
courtship, swimming, walking and
flying. Each of the activities has a
different energy requirement and after
many replications the energy required
for one duck to carry out its daily
activities can be calculated.
Second, researchers estimate the
availability of foods such as snails,
clams, and seeds. This effort, across
the landscape, provides an estimate
of food energy available as well as any
associated depletion rate or seasonal
abundance change. Because not all
food on the marsh is actually utilized
by ducks, crop surveys (examining the
food contents of the harvested bird’s
muscular crop) from hunter-harvested
black ducks then verify food usage,
food preference and the possibility
of any shift in food consumption as
resources become depleted. The final
result of this bioenergetic model will
be an estimate of the carrying capacity
for wintering black ducks.
Current population and harvest
goals can be reassessed in light of
the carrying capacity estimate from
the bioenergetics model. From this,
the amount of habitat creation or
improvement needed to support
a desired black duck population
level can be estimated and resources
available for habitat work can be
balanced against expected population
gains. Information on critical black
duck habitat can also be used to
support wetland protection policies.
Increasing the quantity or quality
of habitat on the wintering grounds,
and in particular New Jersey, should
increase the winter survival of black
ducks and improve the body condition
of hens returning to breeding grounds.
Birds with healthier body conditions at
the start of the long northward travel
back to breeding grounds can result
in increased production and survival
of young, both crucial for achieving a
larger black duck population.
The following partners cooperate to support
this critical black duck research:
New Jersey Division of Fish and Wildlife
Ducks Unlimited, Inc.
U.S. Fish and Wildlife Service
New Jersey Duck Stamp Committee
Black Duck Joint Venture
New Jersey Waterfowlers Association
University of Delaware
Atlantic Coast Joint Venture
VA Dept. of Game & Inland Fisheries
DE Dept. of Natural Resources &
Environmental Control
OH Dept. of Natural Resources
Southern Illinois University
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August 2008 For more information contact New Jersey New Jersey Fish & Wildlife Digest | 77
Division of Fish and Wildlife at (609)292-2965 2008 Hunting and Trapping Issue