Background Information:
The bald eagle seen as the figure head of the nation, lies on the verge of a comeback. Listed under the family Acccipitidae and known under the Latin name Haliaeetus Leucocepalus
it was enlisted under the endangered species act throughout the lower 48 states, except in Minnesota, Michigan, Wisconsin, Washington, and Oregon where it was listed as a threatened species. On July 12, 1995, the U.S. Fish and Wildlife Service announced that the bald eagle would be reclassified from endangered to threatened in the lower 48 states, effective August 11, 1995. In those states where the species was already listed as threatened, it remains classified that way. The bald eagle is considered to be one of the greatest success stories since the Endangered Species Act was passed in 1973.
The bald eagle has some major descriptive qualities. The characteristic adult plumage consists of a white head and tail with a dark brown body. Juvenile eagles are completely dark brown and do not fully develop the majestic white head and tail until the fifth or sixth year. Fish are the primary food source but bald eagles will also take a variety of birds, mammals, and turtles, as well as carrion when fish are not readily available. Adults average about three feet from head to tail, weigh approximately 10 to 12 pounds and have a wingspread that can reach seven feet. Generally, female bald eagles are somewhat larger than the males.
Bald eagles mate for life, or until the death of their mate. The breeding season varies throughout the U.S., but typically begins in the winter for the southern populations and progressively shifts towards the spring the further north the populations occur. The typical nest is constructed of large sticks and lined with soft materials such as pine needles and grasses. The nests vary in size, but are typically large measuring up to six feet across and weighing hundreds of pounds. Many nests are believed to be used by the same pair of eagles year after year. Backup nests can also be built within a period of about a week when the eagles begin to ready their nest for the eggs. This is in case the tree may fall in a storm or high winds. Their nests are usually atop a large tree that can support such weight with broken off tops so their wing span can be more easily accommodated. Female eagles lay an average of two eggs; however, the clutch size may range from one to three eggs. The eggs are incubated about 35 days. The young fledge 9 to 14 weeks after hatching and at around 4 months of age the eaglets are on their own. By the time an eaglet leaves the nest its wingspan is larger than that of it's parents. These immature feathers are speckled brown and white and will remain until it becomes an adult. As an eagle matures the feathers become less mottled and the distinct yellow of the beak and feet will slowly begin to appear. In the case of eagle killings this can give markers of age identification of the downed bird or even when visible in the wild.
History of Eagle Killings:
The first massive documented eagle shootings took place in Alaska in 1917 to 1952. This was one of many reasons for the initiation of the decline in the eagle population that lead to the instillation of three major acts to help save the eagle. Helicopter and airplane hunts seem to do the most damage to eagle populations at a much higher rate than traditional hunting roles. Another reason for the decline in eagle populations arises from the annual amount of killings due to electrocution. Electrocution occurs when an eagle's wings are spread so far that the bird touches a power source and the ground at the same time. Leg-hold jaw traps, usually set for coyotes, fur bearers, or other mammals, can severely injure or detain and eagle until it dies as well. If the eagle lives, it may loose a leg or is most likely crippled and can not fend for itself any longer. Other causes of eagle deaths lie in collisions by flying into towers, building, power lines, vehicles, and other obstructions even though their eyesight is 20 times greater than that of humans.
Poisoning deaths began to occur after man started using chemicals such as DDT. DDT causes an eggshell thinning by altering the chemical makeup in the females reproductive system and calcium metabolism. These poisons are ingested through bait and may come in the form of pollutants or contamination from the environment. DDE still has not been banned in the United States and is used as a fertilizer, its affects are somewhat of a long term unknown but still reaches the waterways via precipitation and ground water. The food an eagle prays upon is made up of about 80-90% fish, the amount of contaminates in an eagle is about a half a million times that of what is in the water: caused by bioaccumulation. This gradual effect makes it much harder to realize what is happening over all to the eagle population and in many cases make the effects that of an irreversible one. Habitat destruction and alteration also play large roles in the survival of the eagle. Deforestation makes the land unfit for habitation so that the eagle population is forced to move on. In 1978 when the eagle was declared endangered, lands began to be set aside for them to recuperate from the devastating effects of DDT/PCB and deforestation. Development of shoreline and waterfront timberlands are often the most destructive towards eagle habitat. According to prey based changes, recent studies have shown, and proved that survival may depend on the abundance of food and that improved reproductive success occurs when food is abundant.
Laws:
The Endangered Species Act, mandated that the endangered species be given special protection, research, and management. Section 7 of the Endangered Species Act mandates that actions will be taken or condoned by federal agencies will not jeopardize the "continued existence" of an endangered species. Violators of this act will be fined $20,000 and/or one year of federal imprisonment.
The Bald and Golden Eagle Protection Act defines illegal acts against eagles and their eggs. And is the main safety net of the survival and comeback of the bald eagle today.
The bald eagle has made a comeback, and has been removed from the Endangered Species list because of the awareness of the plight they suffered. They are currently listed as Threatened over most of the US.
Integrating GIS and
Range Data:
As part of the responsibility of insuring the future of the eagle in the
1980's, data analyses such as habitat preference and assessment to the risks of
environmental contaminants spurred the HOME RANGE program into action. It was
initially developed to provide home range estimates based on the abstention of
harmonic mean measure of an animal's activity and other commonly used methods to
function in an ARC/INFO environment. Determination of habitat use patterns is a
common practice for wildlife radio telemetry studies. However, habitat
misclassification can occur because the true location of a radio marked animal
can only be estimated. A new program to correct this can now be used, the SAS
executable file generates random sub sample points from the error distribution of
an estimated animal location and formats the output into ARC/INFO AML creating a
coverage of random points, determines the habitat type at each random point from
an existing habitat coverage, it then sums the number of subsample points by
habitat type for each location, and outputs the results in ASCII format. The
proportion and precision of habitat types used to calculate the sub sample are
taken from points generated for each radio telemetry location.
A possible study would include something like that found in similar large
birds like using satellite telemetry to determine the movement patterns and
soaring altitudes of vultures. Two birds were marked with patagail tags, and
fitted with 100-g satellite transmitters that include a VHF transmitter, they
were then released in a remote forest area and tracked for several days
following release using radio telemetry and subsequently monitored weekly by
satellite. Locations and altitudes are being used to develop a large scale
relocation project for the vultures but similar techniques could be used for
reinstatement of eagle populations into other parts of the country.
In 1989 and 1991 Earthwatch teams in Michigan conducted a survey of their
eagle population growth. Teams helped band nesting bald eagles, collect blood
and feather samples, analyze food remains from under nest sites, and measure
habitat characteristics around nest trees and summer perch sites along river
basins. Teams had also helped trap adult and fledgling eagles, attaching radio
or satellite transmitters to conduct early radio-telemetry surveys to determine
eagles' habitat along tow river basins of the lower peninsula of Michigan. From
these surveys it is possible to find prime nesting sites, where food is most
abundant, and the limiting factors of population density.
The affects of radio transmitters on birds varies. For example smaller
lighter transmitters can be mounted on tail feathers and few effects have been
associated with this attachment. But only relatively small transmitters can be
placed on tails, which limits the longevity or signal strength of the
transmitter. Larger, longer lasting transmitters can be attached on the back by
a harness but there are several undesirable effects that have been associated
with this method. However, some methods such as modeling flight performance,
speed, distance, and carrying capacity. Also, examples of how radio marking
effects can vary among ages, sexes, and seasons.
In 1994, movements of 19 bald eagles have been monitored through this system
in Washington state. Ten of these eagles have provided new information on
juvenile and non-breeding adult movements, home range use, and long-range
migratory movements to British Columbia and southeast Alaska. As of April 1997,
8 satellite platform transmitter terminals (PTT's) were no longer transmitting;
an average lifespan of an eagle is 30-50 years in captivity and slightly lower
in the wild, but the average lifespan of the transmitters is expected to be
about 24 months give or take a 3 month span. Three PTT's expired prematurely,
but of the 2,962 locations received form the 19 PTT's, 62.5% were useful for
identification of long transmission cycles of which had at least one useful
location. The use of PTT locations identify core areas of use, but greatly
overestimate range size and provide little useful information on specific perch
locations. However, this data is instrumental in locating territories of
individuals on distant breeding areas that can not be surveyed locally.
Potential concerns are interference of the vertical PTT antenna on female
copopultation. Recapture and recovery of a carcass showed no skin abrasion or
abnormal wear from the Teflon-ribbon harnesses, consistent with other research
showing low-injury to eagles form backpack-mounted transmitters. The use of
satellite technology over conventional VHF include the quality and quantity of
information gathered; challenges include coordination of programmable cycles and
PTT deployment when faced with the uncertainties of trapping success, recovery
of downed PTT's, and relatively high cost/individual animal and associated risks
are not advisable for small budget studies.
One of the more recent studies include the work of scientists from the Santa
Cruz Predatory Bird Research Group at UC Santa Cruz. The tracked a juvenile bald
eagle's journey into adulthood with a tiny backpack fitted with a lightweight
satellite transmitter that beeped every 10 days. Signals from the satellite,
sent via e-mail to SCPBRG researchers, show that the bird flew some 900 miles in
August from its nest at Lake Shasta, CA, to the vicinity of the Dean River in
central British Columbia. If the eagle and transmitter survive, biologist will
learn how long the bird remains in Canada and whether it returns to its home
range for breeding. The research also paves the way for satellite tagging of
more eagles, as well as falcons, seabirds, and other species of interest.
The advantages over radiotelemetry are numerous, it makes it possible to keep
up with the bird's flight without being lead miles in a matter of minutes. It
took the young eagle only a week to migrate to British Columbia and with just
radiotelemetry poor weather can keep a plane grounded and not all roads are
accessible to track them on ground. This technology will allow one to be able to
track birds that are not assessable by plane and could include birds injured in
oil spills, the cleaned and released. Also it is a new way to gage the
effectiveness of cleanup after such disasters.
If an eagle transmitter works properly, researchers will get a location every
10 days for about 2 years. The backpacks are designed to fail after that time
and the $3,000 transmitters will fall off for possible use in the future if
retrieved. GIS technology is used to map the birds movements and has already
been in use in the restoration of the peregrine falcon.
With the return of eagle populations and the effectiveness of the Endangered
Species Act and Bald/Golden Eagle Preservation Act, clearly the dedication of
all who believe that natural resources and the environment are worth protecting.
Through tracking the flight of the bald eagle it is possible to gain insight in
how to monitor individual populations and time release dates and sights with the
information that is becoming more available though radio transmitters and
satellite data. It is an expensive undertaking but it is worth studying because
it clearly has applications elsewhere.
My perspective:
I am happy to say that although much of this data was collected elsewhere, I
too have had my eagle watching experience. Eagles have always been very close to
my heart and interest me greatly, they are one of my greatest inspirations in
life. Recently I was fishing through data and came across a book called Eagles
Over the River by Jean Clausen and I realized that I know these people and that
the data from counts and sightings is my data as well. Working for the Ferry
Bluff Eagle Council and now under the rehab efforts of Dr. Joe Kelley, many bald
eagles have found a home in Sauk Prairie once again. Many of the stories seem
familiar, and although I am not mentioned, my mentor and my mother's cousin is.
She had and still is working on the bald eagle project as well as other
endangered species. In particular I remember one of the stories in this book,
recorded one a chilly winter day in December of 1991. I will not go into detail,
because if you want to hear it I will tell it to you in person. It is an eagle
watchers tale and this is how we pass the chilly hours of staring through
binoculars at one of the most amazing birds known to me.
I am looking forward to seeing the new data and the survival of these eagles
through their semi-migrational patterns and seeing how the transmitters fare
through cold weather. The topic is a new one and tracking the bald eagle can be
some times an illusive event, maybe this will shed light on more of the habits
and haunts of America's bird.
New Perspective: In the summer of 2000, I found myself with the most
amazing opportunity. Not only was I allowed to view the bird that I
cherished, but also work along side of it. I sat and watched a pair of
adult bald eagles rear their young to fledglings. A sight that most
Americans will never see, but I gave them a chance to. I held a
interpretive program with a spotting scope on a far hill from the nest, where I
had a chance to educate the visitors of the Porcupine Mountains Wilderness State
Park, in Upper Michigan, about eagles and raptors. I sat perched at my
scope for hours listening to the distant calls that seem so distinct yet merry
in laughter. As the chicks grew from little fluffs of down, I observed how
quickly birds really do change into the bird we all know and love. The
children could especially find their first sights uplifting as they peered
through the scope, many times I heard a small squeal out of them as their eyes
lit up with wonder. As the chicks got older and much larger, even than
their parents, people could soon see something they may have considered a golden
eagle. Dark brown and shimmering under the sun of the hills, the eagles
stretched and flapped their wings frequently. The oldest would, in moments,
consider the highest perch and attempt a lift off to make it up there.
Towards the end of the summer it got to be his favorite perch. If you
would like to know more about my summer experiences and view my log, go to Presque
Isle River Nest
Tidbits:
Estimates of the Minimum Daily Flight Distance of the Bald Eagle
Migration Distance (km): 2,500
Days: 35
Minimum Daily Distance (km): 74
Days Needed If Daily Distance Equals 220 km: 11.4
Information on Migration Motion of the Bald Eagle
Altitude (m AGL): <50->1,000
Method and Topographic Situation: Radio telemetry, VE, mountains and prairie,
United States and Canada
Resource Sites: Books... Internet Sites...
