Amplified birdstrike risks related to population increases of large birds in North America

Abstract

Bird-aircraft collisions (bird strikes) are an increasing safety and economic concern to the civil aviation industry worldwide, costing well over $1 billion each year. To reduce risks associated with strikes, the U.S. Federal Aviation Administration has developed airworthiness standards for airframes, windshields, and engines using a single 4-lb (1.82-kg) bird mass as the maximum that must be tested for most components. We determined that 36 of the approximately 650 bird species that nest in North America have average body masses greater than 4 lbs. Of the 31 species for which population trend data were available, 24 (77%) showed population increases over the past 20-40 years, only 2 showed declines and 5 were stable. Of most importance, 13 of the 14 species with body masses over 8 lbs (3.64 kg) showed population increases. At least 294 strikes with >4-lb birds caused substantial damage to civil aircraft in the USA, 1990-2002; 30% of these strikes involved multiple birds. Over 6,022 strikes occurred at heights >1,000 feet above ground level of which at least 1,986 (33%) involved >4-lb birds. We conclude that airworthiness standards, as well as proposals to allow high-speed (>250 knots [288 miles/hour]) operations below 10,000 feet, should be reevaluated to address the threat posed by increased populations of large flocking birds. Also, increased research and development is needed in the deployment of bird-detecting radar to warn pilots of flocks of migrating birds and in techniques to make aircraft more visible to birds. Finally, wildlife biologists should increase efforts to reduce or disperse populations of these large birds in airport environments. For certain overabundant large species such as non-migratory Canada geese (Branta Canadensis), management programs may be needed to reduce populations regionally.

Full text

INTERNATIONAL BIRD STRIKE COMMITTEE IBSC26/WP-OS4
Warsaw, 5-9 May 2003
AMPLIFIED BIRD-STRIKE RISKS RELATED TO POPULATION INCREASES OF LARGE
BIRDS IN NORTH AMERICA
Richard A. Dolbeer Dr1 & Paul Eschenfelder Capt.2
1 U.S. Department of Agriculture, Wildlife Services, National Coordinator for Airports Safety
and Assistance Program, 6100 Columbus Avenue, Sandusky, Ohio 44870 USA
Tel: +1-419-625-0242, Fax: +1-419-625-8465
Email: richard.a.dolbeer@usda.gov
2 Air Line Pilots Association, 16326 Cranwood, Spring, Texas, 77379 USA
Tel: +1-281-370-3925, Fax: +1-281-370-3925
Email: eschenfelder@compuserve.com
Abstract
Bird-aircraft collisions (bird strikes) are an increasing safety and economic concern to
the civil aviation industry worldwide, costing well over $1 billion each year. To reduce risks
associated with strikes, the U.S. Federal Aviation Administration has developed
airworthiness standards for airframes, windshields, and engines using a single 4-lb (1.82-kg)
bird mass as the maximum that must be tested for most components. We determined that 36
of the approximately 650 bird species that nest in North America have average body masses
greater than 4 lbs. Of the 31 species for which population trend data were available, 24
(77%) showed population increases over the past 20-40 years, only 2 showed declines and 5
were stable. Of most importance, 13 of the 14 species with body masses over 8 lbs (3.64 kg)
showed population increases. At least 294 strikes with >4-lb birds caused substantial
damage to civil aircraft in the USA, 1990-2002; 30% of these strikes involved multiple birds.
Over 6,022 strikes occurred at heights >1,000 feet above ground level of which at least 1,986
(33%) involved >4-lb birds. We conclude that airworthiness standards, as well as proposals
to allow high-speed (>250 knots [288 miles/hour]) operations below 10,000 feet, should be
reevaluated to address the threat posed by increased populations of large flocking birds.
Also, increased research and development is needed in the deployment of bird-detecting
radar to warn pilots of flocks of migrating birds and in techniques to make aircraft more
visible to birds. Finally, wildlife biologists should increase efforts to reduce or disperse
populations of these large birds in airport environments. For certain overabundant large
species such as non-migratory Canada geese (Branta Canadensis), management programs
may be needed to reduce populations regionally.
Key words: aircraft, airframe, airport, bird, bird strike, engine, Federal Aviation
Administration, mass, safety, standards, windshield

IBSC26/WP-OS4 50
1. Introduction
Aircraft collisions with birds (bird strikes) are a serious economic and safety problem. Cleary
et al. (2002) estimated wildlife strikes (98% involving birds) cost the civil aviation industry in
the USA over $400 million/year, 1990-2001. ALLAN & OROSZ (2001) projected that bird strikes
annually cost commercial aviation over $1.2 billion worldwide in 1999-2000. At least 138
people died worldwide as a result of bird strikes from 1990-2002 (THORPE 1996, 1998,
RICHARDSON & WEST 2000; DOLBEER, unpublished data).
About 71% of bird strikes to civil aircraft occur below 500 feet above ground level (AGL)
during takeoff and landing (CLEARY et al. 2002). Thus, implementation of integrated
management programs to reduce bird populations in airport environments is essential to
minimize bird strikes (CLEARY & DOLBEER 1999). However, given the diversity and mobility of
avian species, programs to manage bird hazards at airports will never exclude all birds from
aircraft movement areas (e.g. DOLBEER 1999) and will do nothing to prevent strikes outside
the airport environment. Therefore, a second critical component to reduce the hazards and
economic costs of bird strikes is the development of airworthiness standards for airframes,
windshields and engines, including shielding of important aircraft systems, that ensure
aircraft can operate safely in the event of a bird strike. A third component involves the
restriction of airspeeds to 250 knots (288 miles/hour) below 10,000 feet when birds are
present (Code of Federal Regulations 2002).
The U.S. Federal Aviation Administration (FAA) has developed airworthiness standards for
airframes and windshields of transport aircraft (>19 passenger seats) using a single 4-lb
(1.82 kg) bird as the maximum-sized mass that must be tested (with the exception of 8 lbs
[3.64 kg] for the empennage). Standards for commuter aircraft (10-19 seats) are less
stringent [Table 1]. The maximum mass required for turbine-engine testing is a single 4-lb
bird for engines currently in service. The engine does not have to keep operating after a 4-lb
bird ingestion to pass these standards; rather, the engine must contain the damage, not
catch fire, and be capable of shut-down [Tabel 1]. MACKINNON et al. (2001) provide a more
detailed discussion of airworthiness standards related to bird strikes.
Aggressive programs by natural resource and environmental organizations during the past
30 years (e.g. pesticide regulation, expansion of wildlife refuge systems, wetlands
restoration), coupled with land-use changes, have resulted in dramatic increases in
populations of many wildlife species in North America (DOLBEER 2000) and Europe (BUURMA
1996, ALLAN & FEARE 1996). In addition, certain of these wildlife species that are a proven
threat to aviation, such as Canada geese (CLEARY et al. 2000), have adapted to urban
environments (SMITH et al. 1999), making the risk of wildlife strikes at airports much greater.
Because of concern within the aviation industry with populations of large bird species (e.g.
MACKINNON et al. 2001, ESCHENFELDER 2001), an FAA/European Joint Aviation Authority
(JAA) working group (Aviation Rulemaking Advisory Committee) has proposed a new
standard requiring future large engines to demonstrate 20 minutes of run-on after ingestion
of an 8-lb bird. Finally, these population increases of large birds should be factored into risk
analyses regarding proposals to allow commercial aircraft to use high-speed (over 250 knot)
operations below 10,000 feet to facilitate air traffic flow (Code of Federal Regulations 2002,
National Transportation Safety Board 1999).
To help clarify these issues, we surveyed the avian literature to determine the number,
flocking characteristics, and population status of bird species with body masses greater than
4 and 8 lbs that inhabit North America. In addition, we determined the reported number of
single and multiple bird strikes involving these species for civil aircraft in the USA, 1990-2002
and the damage characteristics of these strikes. Finally, we determined the reported number

IBSC26/WP-OS4 51
of strikes at heights from 1,000-10,000 feet and above 10,000 feet AGL for all bird species
and for species >4 lbs. Our goal is to provide objective data on the numbers, population
trends, flocking characteristics, and strike patterns for these large bird species to aide
regulatory bodies, engineers, and biologists in developing standards and strategies to reduce
the costs and hazards of bird strikes.
2. Methods
ALSOP (2001) was our primary reference source to initially screen, from the approximately
650 bird species that nest in North America (USA, Canada, and Caribbean Islands), those
species having a mean body mass approximating 4 lbs or more. This list was refined by
examining data on avian body masses from DUNNING (1993) and other sources. Those
species included in the final list had a mean body mass >4.0 lbs for at least one gender, or if
data were unavailable by gender, a mean body mass >4.0 lbs for unknown gender.
We obtained population data (numbers of birds and mean annual % change in numbers) for
each species from various sources such as the North American Breeding Bird Survey (BBS),
Christmas Bird Counts (CBC), North American Waterfowl Survey reports, North America
Waterbird Conservation Plan, and the scientific literature. For BBS or CBC data, populations
were classified to be increasing or decreasing if a significant (P < 0.05) mean annual percent
change was detected for the years considered (generally 1966-2001 for BBS data, 1970-
2001 for CBC data; SAUER et al. 2002, National Audubon Society 2003a). For other species,
we calculated the mean annual percent change from a baseline year (earliest year [1959-
1987] for which a reliable population estimate was available) and the most current (1995-
2002) population estimate (BELANT & DOLBEER 1993). Sources of information and scientific
names for each species are listed in Appendix 1.
We subjectively classified the social behavior of each species relevant to bird strikes as
strongly flocking, limited flocking, or generally solitary based on our general knowledge of the
species and discussions among ornithologists. We also classified each species as soaring or
non-soaring. Finally, we determined the number and characteristics of reported strikes to civil
aircraft in the USA involving these species, 1990-2002 (CLEARY et al. 2002, S.E. WRIGHT,
U.S. Department of Agriculture, unpublished data).
3. Results
3.1 Population increases of large birds
Thirty-six species, about 6% of the approximately 650 species that breed in North America,
had mean body masses >4 lbs for at least 1 gender [Appendix 2]. Of the 31 species for which
a population trend could be estimated, 24 (77%) indicated increases, 2 (6%) indicated
declines and 5 (16%) were stable [Table 2]. All 13 (100%) of the 14 species with body
masses above 8 lbs for which a population trend could be estimated indicated population
increases.
3.2 Flocking characteristics of large birds
Twenty-four (67%) of the 36 species exhibit strong flocking behavior, 9 (25%) exhibit limited
flocking behavior, and only 3 (8%) exhibit solitary behavior [Tables 2, Appendix 3]. Five
(14%) of the species regularly exhibit soaring behavior.

IBSC26/WP-OS4 52
3.3 Reported bird strikes with large birds
Twenty-one of the 36 species were identified as involved in a total of 1,234 reported strikes
with civil aircraft in the USA, 1990-2002 [Appendix 3]. In addition, there were 561 strikes
reported that involved >4-lb birds (i.e. geese, vultures, eagles, pelicans, swans, cormorants,
albatrosses, cranes, loons) in which the species was not identified. In these 1,795 reports of
strikes with >4-lb birds, 894 (50%) indicated damage and 294 (16%) indicated substantial
damage to the aircraft [Table 3]. Multiple birds were involved in 536 (30%) of the reported
strikes. Birds with body masses >8 lbs were involved in 1,205 strikes of which 615 (51%)
indicated damage and 190 (15%) indicated substantial damage. Multiple birds were involved
in 468 (39%) of the strikes with >8-lb species. Sixteen (76%) of the 21 struck species with
body masses >4 lbs have exhibited population increases; all 9 (100%) of the struck species
with body masses >8 lbs showed population increases. Nineteen (90%) of the 21 struck
species exhibit strong (14) or limited (5) flocking behavior.
3.4 Reported bird strikes with large birds at heights >1,000 feet AGL
From 1990-2002, 6,022 (19%) of the 31,453 reported bird strikes (where height AGL was
indicated) were at heights >1,000 feet AGL [Table 4]. The species or species group was
identified in only 1,299 (22%) of these 6,022 cases. Because 427 (33%) of the 1,299
identified birds were species with body masses >4 lbs, we estimate that 1,559 (33%) of the
4,723 unknown birds struck at >1,000 feet AGL were species with body masses >4 lbs.
Thus, we projected that a total of 1,986 reported strikes at >1,000 feet AGL involved >4-lb
birds and that 1,963 of these strikes occurred between 1,001-10,000 feet. Substantial
damage was indicated in 313 of the strikes above 1,000 feet, with 95% (298) of these
substantial-damage strikes occurring between 1,001-10,000 feet. The 3,000-foot vertical
zone between 1,001 and 4,000 feet contained 75% of the strikes within the 9,000-foot zone
from 1,001 to 10,000 feet.
4. Discussion
Populations of most large (>4-lb) bird species in North America, including at least 13 of the
14 species with body masses >8 lbs, have shown substantial increases during the past 20-40
years. A few of these species, such as sage grouse and yellow-billed loons, are unlikely to
be struck by aircraft. However, many of these large species, such as Canada geese, turkey
vultures, great blue herons, bald eagles, snow geese, brown pelicans, sandhill cranes, and
double-crested cormorants, have been struck numerous times during the past 13 years in the
USA. These strikes have often involved multiple birds and substantial damage. We also note
that 57% the 45,341 bird-strike reports in the FAA Wildlife Strike Database, 1990-2002, list
the species struck as unknown (see CLEARY et al. 2002). Furthermore, an estimated 80% of
strikes to civil aircraft in the USA go unreported (CLEARY et al. 2000). Thus, the number of
strikes reported for large (>4-lb) species [Tables 3, 4, Appendix 3] should be considered an
index of strikes and not an actual measure of strike rates. Undoubtedly, there have been
many strikes with >4-lb birds (including some of the 15 species with no strikes recorded) that
either have not been reported or reported as unknown species. Finally, we note that
population increases of large-bird species have not been restricted to North America.
Populations of large species such as great cormorants and Canada geese have shown
dramatic increases in Europe over the past decade (BUURMA 1996, ALLAN & FEARE 1996).
Our analysis clearly indicates that aviation regulatory and industry groups need to reexamine
existing airworthiness standards with regard to bird-strike tolerances. Many of the regulations
have not been revised since the 1970s when large-bird (>4 lbs) populations were much
lower. Of particular concern is that existing standards for transport aircraft regarding large
birds (in most cases 4 lbs being the maximum tested) do not consider multiple-bird strikes.

IBSC26/WP-OS4 53
Yet, our data for 1990-2002 indicate 30% of strikes with >4-lb birds and 39% of strikes with
>8-lb birds have involved multiple birds (see also BUDGEY & ALLAN 1999). The fact that
current large-bird standards for engines only require that the damage be contained and that
the engine can be shut down safely has serious implications for multiple-bird strikes. Such an
incident occurred with a Boeing 707 (E-3 AWACS) aircraft that crashed at Elmendorf Air
Force Base, Alaska, after ingesting Canada geese into 2 engines during take off in 1995
(CLEARY &DOLBEER 1999). Over 80% of transport aircraft in operation by 2010 will have only
2 engines (DOLBEER 2000). Although beyond the scope of this paper, detailed analysis of
data from the long-term bird-strike databases that are now available (e.g. CLEARY et al. 2002)
should be invaluable in objectively guiding decisions regarding bird-strike airworthiness
standards for transport, commuter, and general-aviation aircraft (e.g. MARTINDALE & REED
1998).
Although revisions in airworthiness standards may be needed in response to increased
populations of large flocking and soaring birds, existing aircraft and engines certified under
current (single 4-lb bird) standards will remain in service for many years (ALGE 1999).
Furthermore, even if standards are revised and engineering improvements are made, it will
be impossible to completely “bird-proof” engines and airframes against high-speed collisions
with birds of large mass or flocks of smaller birds. For example, a 4-lb bird struck by a
transport aircraft going 150 knots generates about 14,000 lbs of impact force whereas the
same airplane striking the same bird at 250 and 350 knots generates impact forces of about
38,000 and 74,000 lbs, respectively (MACKINNON et al. 2001). A collision with a 15-lb bird at
these respective speeds generates forces of 20,000, 57,000 and 111,700 lbs. Obviously, if
airframe and engine design cannot be altered, the manner in which the aircraft are operated
must be changed.
Proposals to allow commercial aircraft to use high-speed (over 250 knot) operations below
10,000 feet AGL to facilitate air traffic flow (National Transportation Safety Board 1999)
should be reevaluated in light of the documented increase in populations of large-mass birds
and the substantial number of bird strikes that occur between 1,000-10,000 feet (5,792
reported for civil aircraft in USA since 1990 of which an estimated 1,963 involved >4-lb birds
and at least 101 resulted in substantial damage to the aircraft). Because of a fundamental
relationship between energy (e), mass (m), and velocity (v) expressed in the equation e = ½
mv2, aircraft velocity is even more critical than bird mass in determining the energy imparted
to an aircraft by a strike. For example, a 20% increase in bird mass results in a 20% increase
in energy on impact whereas a 20% increase in aircraft velocity (e.g. from 250 to 300 knots)
results in a 44% increase in energy imparted. An incident in which a Boeing 727 aircraft was
heavily damaged after striking 3-5 snow geese at 6,000 feet during a high-speed (280-knot)
departure from Houston, Texas in January 1998 confirmed the danger to aircraft of high-
speed impacts with large birds (CLEARY & DOLBEER 1999).
Another potential means of reducing strikes with large birds involves the enhancement of
sensory cues emitted by aircraft that are relevant to birds (e.g. light at certain pulse rates or
wavelengths). Previous research has indicated that birds are less able to avoid quieter,
modern jet aircraft (Chapter 3, International Civil Aviation Organization 1993) than older,
noisier (Chapter 2) aircraft (BURGER 1983, KELLY et al. 1999). With quieter aircraft in
operation today (Chapter 2 aircraft engines will be phased out by 2005), new technologies
are needed to enhance the visibility of aircraft to birds. Research into the behavioral
response of birds to approaching aircraft (KELLY et al. 1999) and avian vision (BLACKWELL
2002) may lead to practical methods of enhancing the ability of birds to avoid aircraft.
Finally, it is imperative that aviation regulatory agencies worldwide develop and maintain
rigorous standards for bird-hazard management programs at airports that emphasize the
threat posed by birds and the need to minimize their presence in the airport environment

IBSC26/WP-OS4 54
(CLEARY & DOLBEER 1999, DOLBEER et al. 2000). Aggressive management programs at
airports carried out by professional biologists have been successful in reducing strikes (e.g.
DOLBEER 1999). For certain overabundant large species, such as non-migratory Canada
geese in North America, management programs may be needed to reduce populations
regionally (COOPER & KEEFE, 1997). In addition, the deployment of bird-detecting radar
systems to alert pilots and Air Traffic Control personnel may also prove useful in avoiding
strikes with large flocking birds, especially during periods of migration (KELLY et al. 2001,
BLOKPOEL & MACKINNON 2001).
5. Acknowledgments
The bird strike database used in this analysis was supported by the U.S. FAA, William
Hughes Technical Center, Atlantic City, New Jersey under agreement DTFA03-99-X-90001
with the U S. Department of Agriculture. Opinions expressed in this study do not necessarily
reflect current FAA policy decisions regarding the control of wildlife on or near airports. We
appreciate the support and advice of FAA employees S. Agrawal, E. C. Cleary, and M.
Hoven. We gratefully acknowledge the assistance of S. C. Barras, G. E. Bernhardt, B. T.
MacKinnon, J. L. Seubert, R. Sowden, and the staff of the Engineering and Safety
Department, Air Line Pilots Association, who provided technical information and advice on
the manuscript. S. E. Wright assisted with the analysis of bird strike data.
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National Audubon Society. 2003b. Red-faced cormorant. www.audubon.org/bird/watchlist/
National Transportation Safety Board. 1999. Safety Recommendations A-99-86 to A-99-94.
Report to Administrator, Federal Aviation Administration by National Transportation
Safety Board, Washington, DC USA, 19 November 1999.
North American Waterbird Conservation Plan. 2001. Review Draft II - North America
Waterbird Conservation Plan, Volume 1: Seabirds and colonial waterbirds, 23 October

IBSC26/WP-OS4 57
2001, Waterbird Conservation Plan Steering Committee, Washington, DC USA
(www.nacwcp.org/).
NELSON, H. K. 1999. Mute swan populations, distribution and management issues in the
United States and Canada. Pages 125-132 in Proceedings and papers of the 16th
Trumpeter Swan Society meeting. J. R. Balcomb, M. H. Linck, & A. L. Price, editors. St.
Louis, Missouri USA.
North American Loon Fund. 2001. Pacific loon, arctic loon.
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National Wild Turkey Federation. 2003. National Wild Turkey Federation. The return of the
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PARMELEE, D. F. 1992. Snowy owl (Nyctea scandiaca). In The Birds of North America, No. 10
(A. Poole & F. Gill, editors.). The Academy of Natural Sciences, Philadelphia,
Pennsylvania and The American Ornithologists' Union, Washington, DC USA. 20 pages.
PERRY, M. C., P. C. OSTENTON, & E. J. R. LOHNES. 2001. The exotic mute swan (Cygnus olor)
in Chesapeake Bay, USA. Special Report, U.S. Geological Survey, Patuxent Wildlife
Research Center, Laurel, Maryland USA. 6 pages. www.pwrc.usgs.gov/.
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Birding. February: 642-644.
RICE, D. W. 1959. Birds and aircraft on Midway Islands. Special Scientific Report—Wildlife
Number 44. U.S. Fish and Wildlife Service, Washington, DC USA. 49 pages.
RICHARDSON, W. J., & T. WEST. 2000. Serious birdstrike accidents to military aircraft: updated
list and summary. Pages 67-98 in Proceedings of the 25th International Bird Strike
Committee meeting. Amsterdam, The Netherlands.
SAUER, J. R., J. E. HINES, & J. FALLON. 2002. The North American Breeding Bird Survey,
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Wildlife Research Center, Laurel, Maryland USA.
SEAMANS T. W., D. M. HAMERSHOCK, & G. E. BERNHARDT. 1995. Determination of body
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SEUBERT, J. S. 2002. Status of North American Canada goose populations. Bird Strike
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THORPE, J. 1996. Fatalities and destroyed aircraft due to bird strikes, 1912-1995. Pages 17-
31 in Proceedings of the 23rd Bird Strike Committee Europe Meeting. London, England.
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ingestions. Pages 11-22 in Proceedings of the 24th International Bird Strike Committee
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Plant Health Inspection Service, Technical Bulletin 1879, Washington DC USA.
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the Interior, Washington, DC USA. 51 pages.
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data; http://midway.fws.gov/.
U.S. Geological Survey. 2003. Patuxent Wildlife Research Center. Laurel, Maryland USA.
http://whoopers.usgs.gov.

IBSC26/WP-OS4 58
Table 1. Maximum bird masses required in tests for airworthiness standards for
airframes, windshields, and engines for transport- (>19 passenger seats) and
commuter- (10-19 passenger seats) category aircraft, U.S. Federal Aviation
Administration (summarized from MacKinnon et al. 2001)
Aircraft
category Aircraft
component
Federal
Aviation
Regulation
Latest
update of
standard
Max.
bird
mass
(lbs) Comments
Transport Airframe Part 25.571 1978 4 Safely complete flight after striking
1 4-lb bird at design cruise speed
(VC)
Transport Empennage Part 25.631 1970 8 Safely complete flight after striking
1 8-lb bird at VC
Transport Windshield Part 25.775 1977 4 Withstand impact of 4-lb bird w/o
penetration at Vc
Transport/
commuter Turbine
engine Part 33.76 2000 4-8aEngine will not catch fire, have
uncontained failure, or lose
capacity to be shut down
Commuter Airframe/
empennage No standards
Commuter Windshield Part 23.775 1996 2 Withstand impact of 1 2-lb bird at
maximum approach flap speed
(VFE)
a One 4-lb bird for most existing aircraft engines, one 6-lb bird for certain mid-sized engines that may
be developed in the future; one 8-lb bird for large-intake (3.9 m2) engines (RR Trent, P&W 4084,
GE90) for new wide-bodied aircraft such as Boeing 777.

IBSC26/WP-OS4 59
Table 2. Summary of population trend estimates and flocking and soaring characteristics for 36
species of birds in North America with mean body masses >4 lbs [see Appendices 2, 3]
Species exhibiting population: Species exhibitinga: Body-
mass
category
Number
of
species In-
crease De-
crease Sta-
bility Un-
known Strong
flocking Limited
flocking Solitary
behavior
4-8 lbs 22 11 2 5 4 15 (0) 6 (2) 1 (0)
>8 lbs 14 13 0 0 1 9 (0) 3 (1) 2 (2)
Total 36 24 2 5 5 24 (0) 9 (3) 3 (2)
a Values in parentheses are the number of species exhibiting soaring behavior

IBSC26/WP-OS4 60
Table 3. Number of reported strikes and damaging strikes to civil aircraft in USA from 1990-2002 for
species of birds in North America that have mean body mass >4 lbs [see Appendix 3 and
CLEARY et al. (2002) for more detailed data on individual species]
Reported strikes
Species group Total
number With
damage With substantial
damage a No. (%) involving
>1 bird b
Total (all strikes with species or
species group >4 lbs) c 1,795 894 294 536 (30)
Total (all strikes with species or
species group >8 lbs) c 1,205 615 190 468 (39)
a Aircraft incurs damage or structural failure which adversely affects the structure strength,
performance or flight characteristics of aircraft and which would normally require major repair or
replacement of the affected component (excluded are: bent fairings or cowlings; small dents or
puncture holes in skin; damage to wing tips; antenna, tires or brakes; engine blade damage not
requiring blade replacement) (International Civil Aviation Organization 1989).
b Twenty-six strike reports (18 for birds >8 lbs) did not indicate whether or not multiple birds were
involved. These reports were excluded from total strikes when calculating percent of strikes involving
>1 bird.
c Assuming all albatross, vulture and cormorant strikes in which the species was not identified were
with birds >4 lbs and all unidentified swan, pelican, eagle, crane, loon, and goose strikes were with
birds >8 lbs.

IBSC26/WP-OS4 61
Table 4. Number of reported bird strikes with civil aircraft at heights >1,000 feet above ground level
(AGL) for all birds and for identified species with mean body masses >4 lbs, USA, 1990-
2002. In addition to the data presented in this table, there were 25,431 reported strikes at
0-1,000 feet AGL and 13,888 reported strikes in which height was not indicated.
Number of reported strikes
(all birds) a
Number of reported strikes
(identified species with body mass
>4 lbs)b
Height
(feet AGL) Total With
damage
With
substantial
damage c Total With
damage
With
substantial
damage c
1,001-2,000 2,288 587 138 195 147 48
2,001-3,000 1,340 337 92 118 91 30
3,001-4,000 691 148 31 42 29 9
4,001-5,000 495 99 13 24 20 6
5,001-6,000 354 75 6 17 9 3
6,001-7,000 239 47 6 11 8 3
7,001-8,000 169 38 6 8 5 2
8,001-9,000 91 20 4 4 2 0
9,001-10,000 125 28 2 3 2 0
(1,001-10,000) 5,792 1379 298 422 313 101
>10,000 230 93 15 5 4 0
Total (>1,000) 6,022a1472 313 427
a317 101
a Of the 6,022 bird strikes reported at heights >1,000 feet AGL, the species or species group was
identified in only 1,299 cases (22%) and was classified as unknown bird in 4,723 cases (78%).
Because 427 (33%) of the 1,299 identified birds were species with body masses > 4 lbs, we estimate
that 1,559 (33%) of these 4,723 unknown birds were species with body masses >4 lbs. Thus, we
estimate a total of 1,986 reported strikes at >1,000 feet AGL involved birds >4 lbs and that 1,963 of
these strikes occurred between 1,001-10,000 feet.
b Includes all strikes with vultures, cormorants, swans, pelicans, eagles, albatrosses, and geese that
were not identified to species.
c See footnote a in Table 3.

IBSC26/WP-OS4 62
Appendix 1. Scientific names and sources of information on population status for the 36 species of
birds in North America (Canada, USA [including Hawaiian Islands], and Caribbean) that
have mean body mass for at least 1 gender >4 lbs (body mass data from DUNNING [1993]
except for turkey vultures [SEAMANS et al. 1995] and double-crested cormorants from
Ohio [Unpublished data, M. T. BUR, U.S. Geological Survey]
Mean body mass (lbs)
Common
name Scientific
name Male Fe-
male Unk
sex Maxi-
mum Source of information on population status
Mute
swan Cygnus
olor 26.0 21.3 31.3 NELSON (1999), PERRY et al. (2001), PETRIE
(2002), SAUER et al. (2002)
Trumpeter
swan Cygnus
buccinator 25.1 22.7 CAITHAMER (2001)
California
condor Gymnogyps
californianus 22.3 31.3 California Department of Fish and Game (2002)
Wild
turkey Meleagris
gallopavo 16.3 9.3 DICKSON (2001), National Wild Turkey Federation
(2003)
Tundra
swan Cygnus
columbianus 15.7 13.7 21.2 U.S. Fish and Wildlife Service (2002)
American
white pelican Pelecanus
erythrorhynchos 15.4 30.0 Sauer et al. (2002), KUSHLAN et al. (2002)
Whooping
crane Grus
americana 12.8 14.0 MEINE & ARCHIBALD (1996), U.S. Geological Survey
(2003)
Sandhill
crane Grus
canadensis 12.8 11.8 14.8 MEINE & ARCHIBALD (1996), SAUER et al. (2002), ),
International Crane Foundation (2003)
Yellow-billed
loon Gavia
adamsii 12.1 14.1 EARNST (2001)
Bald
eagle Haliaeetus
leucocephalus 9.1 11.8 14.1 BUEHLER (2000), SAUER et al. (2002), U.S. Fish
and Wildlife Service (2003a)
Golden
eagle Aquila
chrysaetos 7.7 10.8 SAUER et al. (2002)
Canada
goose Branta
canadensis 9.2 7.8 10.4
SEUBERT (2002), SAUER et al. (2002), U.S. Fish
and Wildlife Service (2002)
Common
loon Gavia
immer 9.1 9.9 MCINTYRE & BARR (1997), SAUER et al. (2002),
Brown
pelican Pelecanus
occidentalis 8.2 8.1 SAUER et al. (2002), KUSHLAN et al. (2002)
Greater
flamingo Phoenicopterus
ruber 7.8 5.6 9.0
ESPINOZA et al. (2000), BALDASSARRE & AGENGO
(2000)
Snow
goose Chen
caerulescens 7.6 6.8 U.S. Fish and Wildlife Service (2002)
Arctic
loon Gavia
artica 7.4 7.5 North American Loon Fund (2001)
Laysan
albatross Phoebastria
immutabilis 7.1 6.3 9.0
FISHER (1966), Dolbeer et al. 1996, U.S. Fish and
Wildlife Service (2003b), N. A. Waterbird
Conservation Plan (2001)
Greater sage
grouse Centrocercus
urophasianus 7.0 3.9 Braun (1999)
Black-footed
albatross Phoebastria
nigripes 6.9 Rice (1959), U.S. Fish and Wildlife Service
(2003b), KUSHLAN et al. (2002)
Northern
gannet Morus
bassanus 6.5 6.8 8.0
National Audubon Society (2003a), KUSHLAN et al.
(2002)
Emperor
goose Chen
canagica 6.1 6.9 U.S. Fish and Wildlife Service (2002)
Greater white-
fronted goose Anser
albifrons 6.0 5.4 7.1 U.S. Fish and Wildlife Service (2002)
Wood
stork Mycteria
americana 6.0 4.5 University of Georgia (2003), KUSHLAN et al.
(2002)
Continued

IBSC26/WP-OS4-Appendix 63
Appendix 1 (Continued)
Mean body mass (lbs)
Common
name Scientific
name Male Fe-
male Unk
sex Maxi-
mum Source of information on population status
Great blue
heron Ardea
herodias 5.7 4.9 SAUER et al. (2002), KUSHLAN et al. (2002)
Red-faced
cormorant Phalacrocorax
urile 5.6 3.9 5.6
KUSHLAN et al. (2002), National Audubon Society
(2003b)
Double-
crested
cormorant
Phalacrocorax
auritus 5.2 4.5 6.4
TYSON et al. (2000), SAUER et al. (2002), KUSHLAN
et al. (2002)
Great
cormorant Phalacrocorax
carbo 5.0 4.3 5.9 KUSHLAN et al (2002)
Snowy
owl Nyctea
scandiaca 4.0 5.0 6.5
PARMELEE (1992), National Audubon Society
(2003a)
Common
eider Somateria
mollissima 4.9 4.2 6.4 GOUDIE et al. (2000)
Black
vulture Coragyps
atratus 4.8 4.4 SAUER et al. (2002)
Brandt's
cormorant Phalacrocorax
penicillatus 4.6 AINLEY et al. (1994), KUSHLAN et al. (2002)
Masked
booby Sula dactyl
latra 4.1 4.6 5.2 KUSHLAN et al. (2002)
Pelagic
cormorant Phalacrocorax
pelagicus 4.5 3.8 5.4
AINLEY et al. (1994), Hobson (1997), Sauer et al.
(2002), KUSHLAN et al (2002)
Turkey
vulture Cathartes
aura 4.0 4.2 4.7 SAUER et al. (2002)
Great black-
backed gull Larus
marinus 4.0 3.3 5.0 SAUER et al. (2002), KUSHLAN et al (2002)

IBSC26/WP-OS4-Appendix 64
Appendix 2. Population status for 36 bird species in North America that have mean body mass for at
least 1 gender >4 lbs [see Appendix 1 for detailed mass data and sources of information]
Population status
Ran
k Species
Mean
mass
(lb) Years
covered Trend MAPCa
Most recent
population
estimatebComments
1 Mute
swan 26.0 1966-2001 Increase 9.6 22,600 Maryland population increased from 5
(1962) to 4,500 (2001)
2 Trumpeter
swan 25.1 1968-2000 Increase 5.9 23,647 Population increased from about 3,722
(1968) to 23,647 (2000)
3 California
condor 22.3 1987-2002 Increase 74 Wild population increased from 0
(1987) to 74 (Nov 2002); 126 captive
4 Wild
turkey 16.3 1959-2000 Increase 6.0 5,400,000 Population increased from 500,000
(1959) to 5,400,000 (2000)
5 Tundra
swan 15.7 1970-2002 Increase 2.0 163,000 Both western and eastern population
are increasing
6 American
white pelican 15.4 1980-2001 Increase 3.5 >120,000 USA population had 5.6% MAPC,
USA/Canada breeding population
estimate
7 Whooping
crane 12.8 1966-2002 Increase 5.6 297 Wild population increased from 42 in
1966 to 297 in 2002
8 Sandhill
crane 12.8 1966-2001 Increase 6.8 650,000
9 Yellow-
billed loon 12.1 1996, 2001 Unknown ~25,000 Alaska population estimated at ~3,000
in 2001
10 Bald
eagle 11.8 1966-1999 Increase 8.5 100,000 Breeding population in contiguous
USA:1,582 (1974), 12,208 (1999)
11 Golden
eagle 10.8 1980-2001 Increase 3.8
12 Canada
goose 9.2 1966-2002 Increase 10.5 5,377,000 Estimate for resident USA population
is about 3,500,000
13 Common
loon 9.1 1966-2001 Increase 2.7 >500,000 Majority of population is in Canada;
USA population >20,000
14 Brown
pelican 8.2 1980-2001 Increase 5.9 193,000
15 Greater
flamingo 7.8 1970s-2000 Increase >245,000 Caribbean Islands, coastal Yucatan
and Venezuela
16 Snow
goosec7.6 1980-2002 Increase 3.5 3,883,000 Greater (eastern) subspecies has
MAPC of 7.5 %, 1970-2001
17 Arctic
loon 7.4 2001 Unknown >100
About 100 individuals nest in extreme
W and NW Alaska
18 Laysan
albatross 7.1 1962-1995 Increase 4.4 1,00,000 776,000 estimated at Midway Atoll in
1996
19 Greater sage
grouse 7.0 1980-1999 Decline >140,000 Estimated decline from 1980 to 1999
was 35-80%.
20 Black-footed
albatross 6.9 1958-1998 Increase 2.2 >148,000 Population trend estimate for Midway
Atoll (40,480 birds in 1998)
21 Northern
gannet 6.8 1970-2001 Increase 13.2 155,000 Population estimate for 2001
22 Emperor
goose 6.1 1984-2002 Stable 59,000
23 Gr. white-
fronted
goose 6.0 1979-2002 Increase 7.2 1,070,000 Trend is for Pacific population; total
population for Pacific and Mid-
continent
24 Wood
stork 6.0 1983-2000 Increase >2.4 >32,000 USA population is about 12,000
25 Great blue
heron 5.7 1966-2001 Increase 2.2 >83,000 Breeding population only
Continued

IBSC26/WP-OS4-Appendix 65
Appendix 2 (continued)
Population status
Rank Species
Mean
mass
(lb) Years
covered Trend MAPCa
Most
recent
population
estimatebComments
26 Red-faced
cormorant 5.6 2001 Stable 130,000
Breeding population estimated at
<50,000
27 Double-cr.
cormorant 5.2 1966-2001 Increase 10.3 >744,000 Great Lakes nesting population
increased from <200 in 1972 to
230,000 in 2000
28 Great
cormorant 5.0 2001 Unknown 11,600 Breeding population only
29 Snowy
owl 5.0 1970-2001 Stable >20,000 20,000 estimated on Banks Island,
Canada (64,000 km2) in 1950s
30 Common
eider 4.9 2000 Unknown >600,000
Winter population estimate is 600,000-
750,000
31 Black
vulture 4.8 1966-2001 Increase 2.8
32 Brandt's
cormorant 4.6 2001 Stable 151,000
33 Masked
booby 4.6 2001 Unknown ~100,000 Body mass data from Hawaii;
Population data from
Caribbean/Hawaii
34 Pelagic
cormorant 4.5 1966-2001 Stable 130,000
35 Turkey
vulture 4.2 1966-2001 Increase 1.5
36 Great
black-
backed gull 4.0 1966-2001 Decline -2.1 121,000 Breeding population
a MAPC = Mean annual percent change for years indicated based either on North American Breeding
Bird Survey estimate or by calculating MAPC from estimated population in first and last year covered
(BELANT & DOLBEER 1993).
b Population estimate for most species represents adult breeding population and does not include
subadult birds.
c Body mass presented is for “greater” subspecies, “lesser” subspecies mean body mass = 6.1 lbs.

IBSC26/WP-OS4-Appendix 66
Appendix 3. Flocking and soaring behavior for 36 species of birds in North America that have mean
body mass for at least 1 gender >4 lbs ranked by number of reported strikes to civil
aircraft in USA from 1990-2002 involving these species.
Reported strikes
Species
Mean
mass
(lb) Flocking/ soaring
behavior a Total
number With
damage
With sub-
stantial
damageb
No. (%)
involving
>1 bird c
Canada goose 9.2 Strong flocking 668 339 112 297
(45)
Turkey vulture 4.2 Limited flocking/soaring 157 93 33 9 (6)
Great blue heron 5.7 Limited flocking 105 18 3 2 (2)
Snow goose 7.6 Strong flocking 45 33 17 23 (51)
Bald eagle 11.8 Limited flocking/soaring 45 17 2 5 (11)
Sandhill crane 12.8 Strong Flocking 42 16 6 14 (34)
Great black-backed gull 4.0 Strong flocking 32 5 5 1 (5)
Snowy owl 5.0 Solitary 32 3 2 0
Wild turkey 16.3 Strong flocking (on ground) 24 5 1 3 (13)
Double-crested cormorant 5.6 Strong flocking 23 11 5 4 (17)
Brown pelican 8.2 Strong flocking 22 11 2 2 (10)
Black vulture 4.8 Strong flocking 15 8 5 3 (20)
Common loon 9.1 Limited flocking 7 4 2 0
Tundra swan 15.7 Strong flocking 3 3 3 2 (67)
Greater white-fronted goose 6.0 Strong flocking 3 3 3 1 (33)
Mute swan 26.0 Strong flocking 2 0 0 1 (50)
Golden eagle 10.8 Solitary/soaring 2 1 1 0
Wood stork 6.0 Strong flocking 2 0 0 0
Common eider 4.9 Strong flocking 2 2 2 1 (50)
Great cormorant 5.0 Strong flocking 2 1 1 2 (100)
Pelagic cormorant 4.5 Strong flocking 1 0 0 0
Trumpeter swan 25.1 Strong flocking 0 0 0 0
California condor 22.3 Solitary /soaring 0 0 0 0
American white pelican 15.4 Strong flocking 0 0 0 0
Whooping crane 12.8 Strong flocking 0 0 0 0
Yellow-billed loon 12.1 Limited flocking 0 0 0 0
Greater flamingo 7.8 Strong flocking 0 0 0 0
Arctic loon 7.4 Limited flocking 0 0 0 0
Laysan albatross 7.1 Strong flocking 0 0 0 0
Greater sage grouse 7.0 Limited flocking (on ground) 0 0 0 0
Black-footed albatross 6.9 Strong flocking 0 0 0 0
Northern gannet 6.8 Strong flocking 0 0 0 0
Emperor goose 6.0 Strong flocking 0 0 0 0
Red-faced cormorant 5.6 Strong flocking 0 0 0 0
Brandt's cormorant 4.6 Strong flocking 0 0 0 0
Masked booby 4.6 Limited flocking 0 0 0 0
Total (all strikes
identified to species) 1,234 573 205 370 (30)
Continued

IBSC26/WP-OS4-Appendix 67
Appendix 3 (continued)
Reported strikes
Species
Mean
mass
(lb) Flocking/ soaring
behavior a Total
number With
damage
With sub-
stantial
damageb
No. (%)
involving
>1 bird c
Geese (unknown species) >8 Strong flocking 359 204 53 140 (40)
Vultures (unknown species) >4 Limited flocking/soaring 167 100 28 21 (13)
Cranes (unknown species) >8 Strong flocking 12 4 1 2 (18)
Eagles (unknown species) >8 Limited flocking/soaring 8 4 2 2 (25)
Pelicans (unknown species) >8 Strong flocking 6 3 2 0
Swans (unknown species) >8 Strong flocking 2 1 0 0
Cormorants (unknown
species) >4 Strong flocking 3 1 0 1 (33)0
Loons (unknown species) ( >8 Limited flocking 3 3 3 0
Albatrosses (unknown
species) >4 Strong flocking 1 1 0 0
Total (all strikes with
species or species group
>4 lbs) 1,795 894 294 536 (30)
Total (all strikes with
species or species group
>8 lbs) d 1,205 615 190 468 (39)
a Strong flocking = Birds normally associate in dense flocks while feeding, traveling or nesting; Limited
flocking = Birds often found in small groups while soaring, migrating, feeding or breeding; Solitary =
Birds normally feed and travel as individuals; Soaring = Birds typically soar while searching for food,
often in loose flocks or “kettles” with other members of same species.
b Aircraft incurs damage or structural failure which adversely affects the structure strength,
performance or flight characteristics of aircraft and which would normally require major repair or
replacement of the affected component (excluded are: bent fairings or cowlings; small dents or
puncture holes in skin; damage to wing tips; antenna, tires or brakes; engine blade damage not
requiring blade replacement, International Civil Aviation Organization 1989).
c A total of 26 strike reports did not indicate whether or not multiple birds were involved: unidentified
goose (10), Canada goose (6), turkey vulture (4), great blue heron (2), sandhill crane (1), brown
pelican (1), unidentified vulture (1), unidentified crane (1). These reports were excluded from total
strikes when calculating percent of strikes involving >1 bird.
d
Assuming all unidentified swan, pelican, eagle, crane, and goose strikes were with birds >8 lbs.