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~oc ~~Ei~coNTROL JGESTED PRACTICES FOR
RAPTOR PROTECTION ON POWER LINES
THE STATE OF THE ART IN 1981
Raptor Research Report No . 4
Raptor Research Foundation, Inc .
1981
I
I
A. Dean Miller
Suggested Practices for
Raptor Protection on Power Lines
The State of the Art in 1981
by
Richard R. Olendorff
Endangered Species Coordinator
California State Office
U.S. Bureau of Land Management
2800 Cottage Way
Sacramento, CA 95825
Supervisor, Transmission Engineering
Public Service Company of Colorado
P.O . Box 840
Robert N. Lehman
Wildlife Biologist
U.S. Bureau of Land Management
2800 Cottage Way
Denver, CO 80201 Sacramento, CA 95825
A report prepared in the public interest , published and distributed for the Edison Electric
Institute by Raptor Research Foundation, % Department of Veterinary Biology, University
of Minnesota, St. Paul, Minnesota 55101.
TABLE OF CONTENTS
TABLE OF CONTENTS ••
ACKNOWLEDGEMENTS .
LIST OF FIGURES. .
HOW TO USE THIS PUBLICATION.
EXECUTIVE SUMMARY .•.
PROLOGUE •
PART ONE:
PART TWO:
THE IDENTIFICATION AND RESOLUTION OF AN ISSUE
THE BIOLOGICAL ASPECTS OF RAPTOR ELECTROCUTION. •
Susceptibility of Raptors to Electrocution • .
Golden Eagle Distribution. • • • • • • • . • •
Geographical Distribution • • • • . . . .
Ecological Distribution . . • • • • . .
Seasonal Patterns . • . . . . • • . . • . . • • .
Physical Characteristics of Golden Eagles.
Size. . . . . . . . . . . . . . . . . . .
EleCtrical Qualities of Feathers and Skin
Golden Eagle Behavior .•••••••.•..•.•.•.•••.
Raptor Use of Power Lines and Related Structures •••
Preferred Poles . . • • • . • • • • . • • • • • . •
Adult vs. Immature Eagle Susceptibility to Electrocution.
Other Behavioral Factors. • • . . . . • • • . . • • . . .
Page
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PART THREE: POWER LINE DESIGN AND MODIFICATION FOR RAPTOR SAFETY. 18
Background and Terminology . . • • . • • • • . • .
Speci fie Design Problems • • . . • • . . • • • • .
Suggested Practices. • • • . . • • • . . • • . .
Pole, Crossarm, and Conductor Configurations.
Armless Construction. • • • .
Undergrounding ••..•••.••••••.•.
Insulation. • • • • . • • • • •
Management of Eagle Perching.
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PART FOUR: OTHER SELECTED MITIGATION METHODS. •
Introduction . . • . . . . ; . . . . . . . . . .
Construction Impacts. . • • • . • • • •
Mitigation of Construction Impacts •••••
Direct Impacts of Line Maintenance. • • • • • . . •
Mitigation of Line Maintenance Impacts ..
Harassment and Persecution Impacts. • •
Mitigation of Shooting Impacts. . • . • • .
Raptor Collisions with Power Lines. • •
Mitigation of Collision Impacts • • • • • • • •
Entanglement. • • • • • • • • • • • • • • • • .
Field and Corona Effects: Impacts and Mitigation ••••••
Habitat Enhancement ••••.••••••••.•..•
Habitat Diversity Versus Raptor Density •.•.•.
Raptor Use of Rower Line Support Structures as Nest
SLJbstrates • . . . . . . . . . . . . . . . . . • .
~rt~nclal Nest Structures for Raptors ••••••.
Nest Structure Project Planning ••••••••••••
The Morlan Nelson Nest Structure Design. • • . • • . • • •
Other Types of Habitat Enhancement ••••••••••••••
PART FIVE: LITERATURE CITED AND ANNOTATED BIBLIOGRAPHY ••
PART SIX: INDEX . . • • • . • • • . • • . • • . . . • .
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llO
ACKNOWLEDGEMENTS
Several people deserve spE;!cial mention for their assistance in the
preparation of this paper. At the U.S. Bureau of Land Management, Cali-
fornia State Office, Robert S. Motroni, Robert N. Lehman, and Dawn E.
Olendorff helped during the life of this project to develop the Raptor
Management Information System on which this publication is based.
Virginia E. Schoeffler assisted in the design of the cover. Anne F.
Russell, Barbara J. Scheller, Barbara Roskelley, and Sharon E. Olendorff
all typed for many hours on the manuscript. The encouragement of managers
at several levels within the Bureau that has allowed the pursuit of pro-
fessional goals within areas of specialized staff expertise is greatly
appreciated.
Within the electric industry, some financial assistance for the proj-
ect was arranged by Richard S. Thorsell, Environmental Project Manager of
the Edison Electric Institute. Louis F. Jones and Jon B. Keller of the
Public Service Company of Colorado did the excellent engineering drawings
(Figures 1-18). Wayne D. VonFeldt, also of Public Service Company of
Colorado, technically edited certain sections involving electric conduct-
ance studies and industry terminology. Biologists, engineers, and manage-
ment personnel from several private electric companies reviewed draft
manuscripts at various stages. Companies which have been particularly
active in developing solutions to the raptor electrocution problem and/or
in reviewing this manuscript include the following:
Idaho Power Company;
Utah Power and Light Company;
Public Service Company of Colorado;
Pacific Gas and Electric Company;
Pacific Power and Light Company;
Southern California Edison Company;
Public Service Company of New Mexico; and
Sierra Pacific Power Company.
Jack M. Lee, Jr., of the Bonneville Power Administration has also been
helpful.
Especially thorough biological review of the manuscript was done by
Morlan W. Nelson of Boise, Idaho; Mark R. Fuller, Ronald A. Joseph, and
James L. Ruos of the U.S. Fish and Wildlife Service; and Karen Steenhof
and Michael N. Kochert of the U.S. Bureau of Land Management, Boise Dis-
trict Office. Other biological comments were received from Erwin L.
Boeker, Dale M. Becker, DavidS. Gilmer, John W. Stoddart, Jr., Darrell I.
Gretz, Richard P. Howard, Joseph R. Murphy, and Clayton M. White.
William Tilton of North Pole, Alaska, did the cover drawing of a Golden
Eagle leaving a power pole.
iv
fig. No.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
LIST OF FIGURES
Title
High Voltage Transmission Structures
Typical Distribution Configurations
Single-phase Problem Design
Three-phase Problem Design
Common Transformer Configurations
Typical Three-phase Corner Configuration
Pole-top Extension
Lowering of Crossarms
Ground Wire Gapping
Single-phase Side-mounting Configuration
Use of Non-conductive Crossarm Braces In
Lieu of Grounded Metal Braces
Installation of Transformer Equipment to
Provide far Raptar Perching
Armless Configurations
Conductor Insulation Alternative
Elevated Perch Construction
Perch Guards
Eagle Nesting Platform
v
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-~------------------------------···---·-···----------··················---·---
HOW TO USE THIS PUBLICATION
"Suggested Practices for Raptor Protection on Power Lines ••• The State
of the Art in 1981" is organized to provide rapid access for a variety of
readers to a thorough but lengthy synthesis of all available information
on the subject. The six parts have different values depending on a
reader's objective and prior knowledge.
"PART ONE: THE IDENTIFICATION AND RESOLUTION OF AN ISSUE" is a les-
son for everyone in successful coordination between conservationists; in-
dustry biologists, engineers, and executives; and government staff biolo-
gists, land managers, and species managers.
"PART TWO: THE BIOLOGICAL ASPECTS OF RAPTOR ELECTROCUTION" presents
the land manager or power line design engineer with a thorough discussion
of the biological reasons for raptor susceptibility to electrocution. A
better understanding of the biological and ecological relationships in-
volved has been an important stimulus to the development of mutual respect
and communication between those interested in solving the electrocution
problem.
"PART THREE: POWER LINE DESIGN AND MODIFICATION FOR RAPTOR SAFETY"
switches the emphasis toward teaching biologists and conservationists
about the electric industry, particularly about the design constraints
which do not allow implementation of every conceivable modification or new
configuration of power lines that would be safe for eagles. The suggested
practices presented in PART THREE have been field tested, for the most
part, and are widely applicable, where needed. However, because of the
vast diversity of line designs and voltages used by different power
companies, across-the-board standards are impractical. Everyone is
cautioned not to pull pages from this report and insist that designs be
precisely as shown or that suggested practices be implemented unneces-
sarily.
"PART FOUR: OTHER SELECTED MITIGATION METHODS" concerns techniques
for mitigating power line construction, maintenance, and operation impacts
--other than electrocution --on rap tors. Land-use planners and those
who develop environmental assessments will benefit from reading PART FOUR
even if they need not be concerned with PARTS ONE through THREE.
Those who seek even more information may facilitate their acquisition
of the original literature on the subject by using "PART FIVE: LITERATURE
CITED AND ANNOTATED BIBLIOGRAPHY." For quick reference to speci fie points
use "PART SIX: INDEX."
Land managers and industry executives who wish only a general over-
view of the contents of this publication, or any part of it, may read the
EXECUTIVE SUMMARY beginning on the following page.
vi
-------------------------~----~-----
EXECUTIVE SUMMARY
PART ONE: THE IDENTIFICATION AND RESOLUTION OF AN ISSUE. Birds of
prey (raptors) are one of the most politically sensitive groups of birds
with which industry, governmental agencies, and conservation organizations
must be concerned. As end-of-the-food-chain organisms, raptors are both
biologically important and environmentally sensitive. Such sensitivities
have created considerable academic interest in these birds and their prob-
lems (such as electrocution by power lines) and have generated great pub-
lic demand for better protection and management of raptor populations and
habitats.
A new dawn for the raptor conservation movement and for the concept of
raptor management occurred during the winter of 1970-1971 in Wyoming and
Colorado. During that winter and the subsequent spring, nearly 1,200
eagle deaths resulting from poisoning (30+), shooting from aircraft
(800+), and electrocution or shooting along power lines (300+) were docu-
mented in agency reports and court testimonies. Continuing discoveries of
dead raptors, primarily immature and subadult Golden Eagles, led to cer-
tain healthy alliances between industry, government, and conservation
organizations dedicated to solving the raptor electrocution problem.
In 1972 the U.S. Rural Electrification Administration published the
first definitive guidance on how to minimize raptor electrocution problems
on power lines. Between 1972 and 1975, knowledge concerning this subject
increased, and a second-generation handbook was produced entitled 11 Sug-
gested Practices for Raptor Protection on Powerlines.11 This publication
is still widely used by industry and government, but will be replaced by
the present report.
Since 1975 several carefully designed research projects involving both
the biological and power line design aspects of the raptor electrocution
issue have been completed. At the same time, the pertinent literature
grew to over 225 references. The following new assessment of this issue
and its solutions 1) reflects what was learned between 1975 and 1981 and
2) synthesizes relevant information from all available sources.
PART TWO: THE BIOLOGICAL ASPECTS OF RAPTOR ELECTROCUTION. Raptors
are electrocuted by power lines because of two seemingly unrelated yet
interactive factors: 1) the distribution, size, behavior, and other bio-
logical aspects of raptors, and 2) designs of electric industry hardware
which place electrical wires close enough together that raptors can simul-
taneously touch two or more of them with their wings or other parts of
their bodies. The corrective measures that have been developed as a re-
sult of recent studies can make both old and new power line configurations
safe for eagles. However, to minimize the biological impacts of various
land uses as well as the constraints placed on power line design engi-
neers, it is necessary that both industrial and governmental planners,
managers, and developers understand the ecological relationships involved.
Vii
Large size is by far the most crucial factor which predisposes certain
raptors to electrocution. Between 70 and 90 percent of all raptor mortal-
ities along electric distribution lines are eagles. Of all such eagle
mortalities, less than 10 percent are Bald Eagles; the others are QJlden
Eagles.
There are an estimated 63,000 QJlden Eagles in the United States south
of Canada during the winter months when most electrocution and shooting
problems occur (Table 1) . Clearly, the QJlden Eagle is neither rare,
threatened, nor endangered. However, the impact of power lines is not the
only factor impinging on QJlden Eagle populations. Thus, public demand,
industry image, power line reliability, and Federal law all require con-
sideration of QJlden Eagles regardless of their current abundance.
The major concentrations of both nesting and wintering QJlden Eagles
are in the intermountain West, particularly in western shrub and grassland
habitats, in combinations of these habitats, and in ecotones between
shrub, grassland, and forest habitats. In particular, greater numbers of
QJlden Eagles are electrocuted where rabbits occur than where only rodents
and birds are found.
Raptors are basically opportunistic and thus utilize power lines and
support structures for a number of purposes, especially perching and nest-
ing. The heaviest use is as hunting perches. "Still" hunting from a
perch is an energetically conservative way to find prey provided good prey
habitat is within an eagle's view from the perch. Some power poles are
"preferred" by the eagles because they provide considerable elevation
above the surrounding terrain, thereby providing the birds a wide range of
vision, easy takeoff, and greater attack speed when hunting. Seeking out
these "preferred" poles by land managers and industry personnel facili-
tates the resolution of some local electrocution problems, but in homo-
geneous habitats one pole would not offer any advantage over another to a
hunting eagle; therefore, corrective measures must be applied more widely.
Studies have shown that most QJlden Eagle mortalities along power
lines (up to 98 percent of identifiable carcasses) are immature or sub-
adult birds, even though the general population is only about 30 to 35
percent younger birds. This disproportionate susceptibility of immatures
and subadults to electrocution involves several factors, but none is more
important than flying and hunting experience. The fact that immature
eagles are generally less adept at maneuvering than adults, especially
when landing and taking off from electric distribution lines, has been
demonstrated by considerable research. Hundreds of hours of actual obser-
vations and analysis of slow-motion 16-mm movies of Morlan W. flelson's
trained immature eagles landing on dummy power poles clearly demonstrated
the problems and led to methods for modifying old power line designs and
planning new construcion to maximize eagle safety.
PART THREE: POWER LINE DESIGN AND MODIFICATION FOR RAPTOR SAFETY.
The basic problems of all power lines which electrocute eagles are:
1) the distance between wires is less than the wingspread of the bird
landing or perching on them; and 2) design practices dictate the grounding
of particular parts of the equipment to prevent damage from lightning
(ground wire placement also decreases effective separation of wires).
viii
Most lines that electrocute raptors are distribution lines (Figure 2) that
carry between 12,000 and 69,000 volts. Higher voltage transmission lines
(Figure 1) pose little electrocution hazard because wire separation is
adequate.
The two main considerations for making electric power poles safe for
eagles are: 1) modifications of existing problem lines (Figures 3 and 4)
and 2) proper design of new facilities. Both approaches are still vitally
necessary, but because of the vast diversity of line designs and voltages
used by different power companies, across-the-board standards and guide-
lines are impractical. Nonetheless, specific problems can be attacked on
a broad front including: 1) design and modification of poles, crossarms,
and wire placements to effect adequate separation of energized hardware;
2) insulation of wires and other hardware where sufficient separation can-
not be attained; and 3) management of eagle perching.
Adequate separation of energized wires, ground wires, and other metal
hardware is the most important factor in preventing raptor electrocu-
tions. The objective is ~ 60-inch (152-cm) minimum separation of conduc-
tors. This can be accomplished in retrofitt1ng old three-phase lines by
lowering the existing crossarm (Figure 8) or by raising the center wire on
a pole-top extension (Figure 7).
Another useful technique is to put 4-inch (10.2-cm) gaps (Figure 9) in
ground wires near energized conductors. Lightning will discharge across
these gaps, but day-to-day safety is provided to the birds because a
gapped ground wire is not actually connected to ground. Leaving the top
20 to 30 inches (50.8 to 76.2 em) of poles free of wires so that eagles
can perch safely is also effective. In addition, the use of grounded
steel crossarm braces should be avoided (Figure 11). As a general rule,
the less grounded metal that is placed near energized wires, the less the
hazard of raptor electrocution.
Armless configurations (Figure 13) and underground placement of wires
present special problems involving reliability and/or cost that in some
circumstances decrease their attractiveness to the industry. However, new
analyses of armless configurations have increased their usefulness in
heavy eagle use areas.
Where adequate separation of conductors and potential conductors can-
not be attained, insulation of wires and other metal equipment may be the
only solution short of redesigning and extensively modifying the line. On
three-phase problem configurations center conductor insulation should ex-
tend a minimum of 3 feet (0.9 m) on either side of the pole-top insulator
(Figure 14).
Two simple and economical methods of making existing problem lines
safe for eagles involve encouraging eagles and other birds to perch on
less dangerous parts of power line support structures. One method is to
install wooden perches 14 to 16 inches (46 to 51 em) above any energized
wire or object so that raptors can sit out of danger (Figure 15). The
second technique is to encourage eagles to perch in non-lethal positions
on power line structures by placing perch guards (Figure 16) in dangerous
ix
areas. Inverted "V" perch guards made of wood, fiberglass, or PVC rod
have shown considerable promise as an economical and effective solution to
many raptor electrocution problems, though tests of these guards are con-
tinuing.
PART FOUR: OTHER SELECTED MITIGATION METHODS. Direct impacts of
power lines on raptors, other than electrocution, are commonly identified
as line construction activities, maintenance impacts, increased vulnera-
bility of perching and nesting raptors to harassment and persecution
(e.g., shooting), increased chances of collisions between raptors and
power lines, entanglement, noise disturbance, and field and corona effects.
The direct impacts of power line construction include: 1) loss of
habitat through right-of-way clearing (where it is done), construction of
access roads, and actual placement of poles, towers, and conductor pulling
sites; and 2) disturbance of raptors through interference with courtship,
nest building, incubation, and foraging activities which leads to deser-
tion of nearby natural nests and roosts. When necessary, mitigation of
these impacts may require preconstruction environmental assessment and
planning, seasonal restrictions on the timing of construction, on-site
analysis of raptor behavior at the time of construction in problem areas,
salvaging deserted eggs or young birds by fostering them to other pairs
away from the impacted area, making maximum use of existing roads and
trails during line constructon, and constructing lines with the aid of
helicopters rather than building new access roads in previously undis-
turbed areas.
The principal impact of line maintenance on raptors is the destruc-
tion, primarily to prevent power outages and electrical fires, of nests
built on poles and towers. Pursuant to the Bald Eagle Protection Act, the
Migratory Bird Treaty Act, and many State wildlife laws, it is illegal
simply to destroy such nests. The most exciting successes in mitigating
the effects of raptor nests on power line support structures involve:
1) moving problem nests to less dangerous places on the structures and
2) placing arti fkial nesting plat forms in safe places on transmission
towers or on dummy poles adjacent to energized lines.
Increased accessibility by man to previously undisturbed areas is
usually the greatest long-term impact of power line construction on wild-
life. This leads directly to shooting by indiscriminant hunters of perch-
ing and nesting raptors. Electrocution is highly selective (over 90 per-
cent) against younger non-breeders; shooting, which is directed more at
the general wintering population, does not discriminate to the same degree
between adult breeders and subadult or immature non-breeders.
Both raptors and industry hardware (e.g., porcelain insulators) would
suffer less shooting damage if power line corridors and roads were sepa-
rated, where practicable, particularly in remote, otherwise undisturbed
areas. If maintenance roads must be built underneath new power lines in
previously inaccessible areas, road or trail closures should be imple-
mented to minimize the access.
X
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Collision of raptors with power lines is not a major problem, although
where endangered species occur, some mitigation may be appropriate. Like-
wise, no significant impacts of electric or magnetic fields, or corona
(e.g., noise, ozone) on perching and nesting raptors have been found.
The habitat enhancement value of power lines must be evaluated on a
number of levels incuding: 1) local versus regional benefits to raptor
populations; 2) direct versus indirect impacts (both negative and posi-
tive); 3) habitat diversity versus species abundance; and 4) aesthetics
versus functionality. For example, functionally, a new power line may
provide raptors with hunting perches and nesting places thereby increasing
habitat diversity and raptor abundance; but, if it also increases the num-
ber of raptors that are shot, then the true habitat enhancement value may
be lessened.
Most raptors which nest on power poles or transmission towers are
species which inhabit open plains, prairies, or savannahs where trees and
cliffs are absent and do not proviae nest sites (Table 2). The Osprey is
a notable exception. The success of power line nests varies from area to
area and between species. Some have speculated that nesting on power
poles and transmission towers is actually extending the breeding range of
some raptors, but more often the result is a local increase of raptor den-
sity within a species' general range.
In any case, interest in artificial nesting platforms as habitat en-
hancement for raptors is very high. Pctual installation of artificial
nesting structures on power poles and transmission towers has been limited
(Table 3), but the success of nest structure programs in general is prom-
ising.
An artificial nest structure design by Morlan W. Nelson (Figure 17) is
of particular importance in that it was developeo primarily for installa-
tion on power transmission towers. The design is intended to minimize
construction time, use of materials, and, thus, cost per structure. Also,
with features to protect nestlings from strong winds and intense sun, the
structures could easily be modified into release stations for raptors for
reintroducing them into areas where they have been extirpated.
xi
PROLOGUE
Whereas cooperation between the electric utility industry, conservation
organizations, and Federal agencies has reduced the occurrence of rap-
tor electrocutions by power lines; and
whereas this cooperation illustrates the effectiveness of coordinated ef-
forts in conserving an important wildlife resource;
Be it resolved that the participants of the 1975 Annual Meeting of the Rap-
tor Research Foundation commend the electric utility industry for its
collective efforts on behalf of raptors; further, the participants
recommend that the industry continue this work.
Resolution passed at the 1975 Annual Meeting of the Raptor Research Foun-
dation, Inc., Boise, Idaho.
xii