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Sheep and People:
Wildlife management of Dall sheep
Management focuses on
managing the interactions between people and wildlife. In fact,
wildlife biologists spend more time managing the activities of people
than they spend working with animals.
is highly valued by all cultures in our society. People value wildlife
as an important resource to use. Just look around you. Much of the
food that we eat comes from domestic animals that are descended
from wild species (e.g. the extinct aurochs is the ancestor of the
modern cow). Some of the clothes we wear are made from both domestic
and wild animals (e.g. leather, fur garments). People also value
wildlife as a source of inspiration: much of our art, literature,
and music focuses on wildlife. Since we are so closely tied to wildlife,
it is no wonder that we can have a significant impact on wildlife
species, especially their abundance and habitat. In this unit, we
will take a closer look at the issues that surround our relationship
with Dall sheep, especially how wildlife managers work to minimize
the harmful effects of our resource use on wildlife populations.
factors can affect sheep populations: habitat loss, overhunting,
introduced disease, malnutrition, and predation. Malnutrition and
predation are referred to as natural factors whereas the
others are human-induced factors. In North America, wildlife
biologists are helping wild sheep populations by correcting and
mitigating human-induced factors. Wild sheep need a place to live
and food to eat, so biologists improve or enhance habitat by prescribing
wildfires that increase the native plants that sheep eat. They provide
safe travel corridors between habitats that are fragmented by human
activities like agriculture and urban development. Wildlife managers
regulate the number of animals that can be killed by hunters to
ensure that the wildlife resource is conserved. Remember that other
animals, predators, also eat wild sheep, so humans have to
learn to share the resource with other animals too. In national
parks, wildlife managers observe the natural factors that affect
wildlife populations and attempt to minimize the impact of humans
while recognizing the important relationship that people have with
Dall Sheep Management in Northwest Alaska:
An important wildlife
management issue in northwest Alaska is the declining Dall sheep
population in the western Baird Mountains. Following two severe
winters in the early 1990's, the population dropped to less than
half its previous size. Without enough sheep to support harvest,
wildlife managers closed sheep hunting seasons for seven years.
This was a classic wildlife management issue - mangers had to decide
what the effect of hunting would be and make decisions regarding
future hunting. The decision to close the season was difficult because
wildlife biologists did not completely understand all of the factors
that caused the population to decline.
To aid managers in the
future, wildlife biologists needed more information on the abundance
of Dall sheep and the natural factors that affect their numbers.
They planned a research study, which began in the spring of 2000,
to provide answers including lamb productivity and survival, adult
survival, nutritional body condition, disease, and movements throughout
the year. The biologists will use radiocollars on approximately
50 sheep for 3 years. Radiocollars will allow the researchers to
follow individual sheep to determine how long they live, how many
lambs they have, and where they travel throughout the seasons. The
second objective of the study is to find the best way to count the
sheep each year. The research team will evaluate several counting
methods. Biologists anticipate that the study will improve their
ability to monitor the sheep population and gain a better understanding
of Dall sheep population dynamics, how the population changes over
Wildlife Research Techniques: The
first step in designing a research study is to think carefully about
the study objectives. What would you like to achieve by completing
the study? NPS wildlife biologists wanted answers to the following
questions about the Dall sheep population:
- How many sheep are
- How long do they live?
- How do they die?
- How many lambs are
born each year?
- How many lambs survive?
- Are sheep healthy?
- What causes the population
to decline or increase?
The next step in designing
a research study is to decide which research techniques or methods
should be used to achieve the study objectives. How will you answer
your questions? The biologists for this study, chose to use two
important research methods: radiocollars and aerial surveys,
which are described in depth below.
Since biologists cannot
study every animal in a population, they select a random sample
of the population — a smaller group of animals randomly selected
from the total population. Biologists study the animals in the random
sample and assume that they represent what is happening to all of
the sheep in the population. For example, if 10% of the sheep in
the sample are killed by wolves each year, biologists assume that
about 10% of the total population of sheep is killed by wolves each
year. Samples allow us to learn about populations without studying
every animal in the population.
and Radiocollaring Sheep:
A radiocollar consists of a radio transmitter attached to a collar.
The collar is put around the neck of an animal just like your dog’s
collar . Collars used for young animals can expand as the animal
grows. Other collars, called break-away collars, deteriorate slowly
with sunlight and fall off the animal after several years, so they
do not have to wear the collar forever. The radio transmitter is
inside a sealed metal box attached permanently to the collar (picture).
A short, flexible antenna sends out a very high frequency radio
signal every second for up to 3 years. The frequency is so high
that neither animals nor people can hear it. Once an animal has
a radiocollar, researchers can return any time and find the animal
to study it. Using a special radio receiver, researchers fly in
small airplanes until they pick up the radiocollar's signal. Each
collar has its own unique frequency, so researchers can know which
animal they are tracking.
of sheep are recorded by GPS (Global Positioning System)
in latitude and longitude coordinates. The GPS is an electronic
receiver that uses signals transmitted by satellites to calculate
the geographic location of the receiver. The locations of sheep
are plotted on maps produced by computers with a GIS, or
Geographic Information System. Researchers look at where sheep live
relative to elevation and vegetation types. They also look at movements
of sheep across the landscape throughout the seasons.
Today, new technology
allows researchers to also use satellite transmitting radiocollars.
Satellite radiocollars look like the conventional radiocollar, but
rather than broadcasting a radio signal to a receiver in airplane,
they send their signal directly to a satellite orbiting 850 km (527
miles) above the earth. The satellite information is processed mathematically
and the location of the animal is sent directly to the researcher
each day by electronic mail. This helps the researcher because rather
than flying several times a year to locate the sheep, they find
out their location every day, just by checking their email. Both
types of collars are being used on this project. So the next question
is: How do you radiocollar a wild sheep?
Wildlife biologists use
a variety of methods to capture wild animals (e.g. tranquilizing
and physical restraint). To capture Dall sheep, wildlife veterinarians
have determined that the best method is to physically restrain sheep
without the use of immobilizing drugs (that make them unable to
move) or tranquilizers (that make them sleepy). Biologists locate
sheep to capture by flying small airplanes. Once a sheep is located,
a helicopter swoops in, and a trained biologist fires a net out
of a modified gun (picture) and entangles the sheep (picture). After
the sheep is entangled, the helicopter lands next to the sheep and
animal handlers blindfold the sheep to keep it calm and then tie
its legs together (hobble) the sheep so it cannot run away. Sheep
are captured during March when they are at lower elevations and
in less steep terrain, that way sheep are less likely to fall and
it is easier to land a helicopter.
the radiocollar is attached to the sheep, and biologists ensure
a good fit allowing for growth and seasonal weight changes that
affect the animal's neck size. While the collar is being attached,
another biologist takes body measurements, weighs the sheep, and
draws a blood sample for later disease screening and a pregnancy
test for ewes. Biologists age each sheep by counting the number
of growth rings on a horn (picture). Each complete ring represents
one year of the sheep’s life. When all of the information is collected,
the sheep’s blindfold and hobbles are removed, and it moves on with
its new radiocollar that will allow biologists to follow it during
the coming years. Biologists will locate each sheep at least one
time each month using an airplane and the signal transmitting from
Sheep - The Aerial Survey: The
most basic method to determine how many sheep are in a population
is to simply count them. Unfortunately, this is harder than it sounds.
Conducting research in the remote areas of Alaska is difficult and
expensive. Most parklands have no roads and with millions of acres,
walking to conduct research is virtually impossible. So, the result
is that most biologists use small airplanes to conduct aerial
surveys to count animals. You would think that a white sheep
on a brown or green slope would be easy to see, but you would be
surprised how hard it is to spot anything from an airplane going
To conduct a census of
the sheep population, biologists are using a population estimation
method called minimum counting with correction. Biologists
draw survey count unit boundaries on topographic maps where each
observer will look for sheep from small airplanes. In the Baird
Mountains, we have 18 count units that encompass nearly 1,980 sq.
km (765 sq. miles). Aerial surveys take place in early July after
all of the snow patches have melted, and lambs are about 1 month
old. Experienced pilots fly biologists across the mountainous terrain
to look for sheep bands within each count unit. When sheep are located,
the biologist records the total number of sheep sighted, the number
of ewes and lambs, and the number and horn-size classes of rams.
Pilots record the locations with an onboard GPS.
Biologists total the
number of sheep seen in all 18 count units to get a minimum count
of sheep in the population. Because biologists cannot possibly see
every single sheep, some sheep may be in rocky terrain or they may
be dirty and just hard to see, they have to adjust the minimum count
to obtain a final population estimate, by adding what is called
a sightability correction factor. An estimate is a
best mathematical guess of the true number of sheep in the population.
Using the radiocollared sheep as an index, if the biologists saw
90% of the radiocollared sheep, then they will add 10% to the minimum
count to get the final population estimate. This describes the simplest
population estimation method. For the Baird Mountains research project,
biologists are also using a more complex estimator called mark-recapture.
Mark-recapture is another
population estimation method, like minimum counting with correction,
but it uses the radiocollared sheep to actually estimate the population
size. Biologists initially mark a sample of sheep with radiocollars
(in this study that means about 50 sheep). The recapture
is actually more appropriately a sighting of a marked animal.
Each day that a researcher flies during the aerial survey and sees
a marked sheep, this is considered a recapture for the estimation
procedure. After multiple “recaptures”, the biologist can use a
mathematical formula that compares the number of marked (radiocollared)
sheep to the number of unmarked sheep seen over the course of several
days to calculate a population estimate. The "Counting Sheep" student
activity will demonstrate more clearly how the procedure works.
Making Decisions: Using
the aerial survey and the radiocollared sheep, biologists can begin
to answer the questions posed earlier. The annual, aerial survey
in July will tell us how many sheep are in the population (our estimate),
and we can compare this to previous years to determine the population
trend. Using information from captured and radiocollared sheep,
we can determine whether sheep are nutritionally healthy based on
their body weight and blood disease screening. We can tell how many
ewes are pregnant and whether we should expect to see a healthy
number of lambs in the following June (remember they were pregnancy
tested in March). We’ll know the average age of sheep in the population
based upon the radiocollared group. Over time we will be able to
see what the life-span of a sheep is and what causes their death.
All of these questions
can be answered by using some simple research techniques, but this
is not the end of the story. What do we do with all of this information?
Remember that wildlife management is the process to manage the interactions
between people and wildlife. The issue in northwest Alaska parklands
is the declining sheep population and the demands of many people
who use the sheep.
In northwest Alaska,
local residents serve as advisors to Federal and State wildlife
managers. Because the issues are complicated and often involve many
people with different ideas about sheep and their value to people,
the NPS regulates the use of sheep in consultation with interested
users. Wildlife managers attempt to blend science and traditional
ecological knowledge to enhance wildlife conservation while respecting
the diverse values that people place on the sheep resource.
So, why do Dall sheep and other wildlife
species matter in your life? Although
that is an easy question to ask, there are many different answers.
First, sheep are an important part of the arctic ecosystem. They
are food for predators, especially wolves. Sheep are important to
both consumptive and non-consumptive users. Consumptive
users are typically hunters. For native subsistence hunters, sheep
are an important food and cultural symbol. For sport hunters, both
the meat and trophy-value of large ram horns are important. For
consumptive use of sheep, there needs to be an adequate population
size to support hunting. Remember that humans are part of the interconnected
ecosystem and their activities affect the entire ecosystem. Wildlife
managers must have the information to make decisions about hunting.
Non-consumptive users may include, photographers, hikers, and floaters
who do not use sheep as a resource, but instead, view them as a
symbol of wilderness and are therefore satisfied knowing that wild
places still exist where sheep can be part of a natural ecosystem.
Like consumptive users, non-consumptive users expect that wildlife
managers are making decisions that will ensure the continued existence
of health sheep populations.
Discuss with your
class the importance of wildlife to ourselves, personally, and to
society as a whole.