BIRDS: Birds at Airports
Birds are a serious hazard
to aviation. A bird or a flock of birds that suddenly
rises from a runway or surrounding area may collide with
incoming or departing aircraft and cause the aircraft to
crash, possibly resulting in the loss of human life.
Bird collision with aircraft is commonly known as “bird
Damage caused to aircraft
usually results from collision of one or more birds with
the engines and/or fuselage. Although most bird strikes
do not result in crashes, they do involve expensive
structural and mechanical damage to aircraft. The
incidence of this problem worldwide makes bird strike a
serious economic problem.
Birds have been a hazard
to aircraft from the first powered flight. During the
early days of
aviation, when aircraft flew at slow speeds, birds had
little difficulty in getting out of the way. Bird
strikes were infrequent and damage was mainly confined
to cracked windshields. The likelihood of the loss of
aircraft and/or human lives was remote. With the
development and introduction of jet aircraft, bird
strikes became a serious hazard and costly problem.
Faster speeds mean birds have less time to react to
approaching aircraft. The force generated by bird impact
with a fast-moving aircraft is tremendous. The newer
turbine engines use light-weight, high-speed mechanical
parts which are vulnerable to bird strike damage.
The Federal Aviation
Administration (FAA) prescribes rules governing wildlife
hazard management at certified airports in the Federal
Aviation Regulations: Part 139. The USDA-APHIS-ADC
program recognizes the potential for aircraft accidents
and loss of human life and considers bird hazards to
aircraft a top priority. This program provides technical
assistance to alleviate bird hazards to civilian
airports and military airbases.
Most bird species are
protected by federal and state laws. The legal status of
problem bird species at airports should be determined
before control is attempted. Migratory birds are
protected under the Migratory Bird Treaty Act of 1918
(16 USC 703-711), while nonmigratory species are
protected under state laws. Some species are further
protected by the Endangered Species Act of 1973 (Pub.
Law 93-205). These laws state make it unlawful to
pursue, capture, take, kill, or possess migratory birds
or endangered and threatened species, except as
permitted by regulations adopted by the secretary of the
interior. Permits to take nonendangered migratory birds
are issued only when the birds are causing, or have the
potential to cause, a serious threat to public health
and safety and when nonlethal methods have failed to
solve the problem. A state permit also may be required
to control migratory and nonmigratory birds protected by
No two airports are
exactly alike. Accordingly, bird hazards vary from
airport to airport, even when the same species are
involved. The occurrence of birds at airports varies
according to habitat availability, weather, season of
year, and time of day.
Bird Attractants at Airports
Airports provide a wide
variety of natural and human-made habitats that offer
food, water, and cover. Many airports are located along
migratory routes used by birds. One of the first steps
in reducing bird hazards is to recognize these
attractants. Usually, several attractants acting in
combination are responsible for the presence of birds
and their behavior at an airport.
Food. Birds require
relatively large amounts of food. Most airports support
an abundance and variety of foods such as seeds,
berries, grass, insects, grubs, earthworms, small birds,
and small mammals. Seeds and berries are sought by
several migratory and resident birds such as sparrows,
finches, starlings, blackbirds, mourning doves, common
pigeons, and waterfowl. Geese are attracted to open
expanses of grasses. Gulls, starlings, robins, and crows
often feed on earthworms on the surface of the ground
following a rain. Gulls are opportunistic feeders and
frequently feed on grasshoppers and ground-nesting
birds. Raptors are attracted to airports because of
rodents, birds, and other small animals that harbored by
tall, poorly maintained grass stands and borders.
Occasionally, food becomes
available through careless waste disposal practices by
restaurants and airline flight kitchens. Airport
personnel have been known to feed birds during their
lunch breaks. Many airports have inadequate garbage
disposal systems that permit access to various food
items. These are a favorite of several species of birds,
especially gulls. Nearby landfills or sewage outlets may
also provide food for birds and other wildlife.
Landfills are often
located on or near airports because both are often built
on publicly owned lands. In these circumstances,
landfills contribute to bird strike hazards by providing
food sources and loafing areas that attract and support
thousands of gulls, starlings, pigeons, and other
species. Generally, landfills are a major attraction for
gulls, the most common bird involved in bird strikes.
Waste paper, paper bags, and other litter blowing across
the ground attract gulls, presumably because litter is
mistaken for other gulls or for food. A gull that is
attracted to litter decoys other gulls and encourages
Water. Birds of all types
are drawn to open water for drinking, bathing, feeding,
loafing, roosting, and protection. Rainy periods provide
temporary water pools at many airports. Many airports
have permanent bodies of water near or between runways
for landscaping, flood control, or wastewater purposes.
These permanent sources of water provide a variety of
bird foods, including small fish, tadpoles, frogs,
insect larvae, other invertebrates, and edible aquatic
plants. Temporary and permanent waters, including ponds,
borrow pits, sumps, swamps, and lakes, attract gulls,
waterfowl, shorebirds, and marsh birds. Fresh water is
especially attractive in coastal areas.
Cover. Birds need cover
for resting, loafing, roosting, and nesting. Trees,
brushy areas, weed patches, shrubs, and airport
structures often provide suitable habitat to meet these
requirements. Almost any area that is free from human
disturbance may provide a suitable roosting site for one
or more species of birds. Starlings, pigeons, house
sparrows, and swallows often roost or nest in large
numbers in airport buildings or nearby trees, shrubs, or
hedges. Large concentrations of blackbirds and starlings
are attracted to woody thickets for winter roosting
cover. Gulls often find safety on or near runways of
coastal airports when storms prevent their roosting at
sea, on islands, or on coastal bays.
Many airports are located
along traditional annual bird migration routes. Birds
may suddenly appear in large flocks on or over an
airport on their annual migration, even when the airport
itself offers no particular attraction. Dates of
migration vary by species and area. Flock size of a
given species may vary widely from year to year
depending on time of year, weather conditions, and many
gulls, and other birds often make daily flights across
airports from their feeding, roosting, nesting, and
loafing areas. Airports near cities may experience early
morning and late afternoon roosting or feeding flights
of thousands of starlings.
Damage Prevention and Control Methods
Bird strike hazards
reoccur regularly at many airports and require constant
attention. Before attempting to reduce bird hazards at
an airport, it is important to assess the problem,
identify contributing factors, and analyze the threat to
aircraft and human safety. A wildlife hazard management
plan should be implemented (and may be required by FAA)
to make the airport unattractive to birds. Scaring or
dispersing birds away from airports is usually difficult
because birds are tenaciously attracted to available
food, water, and cover. As long as these attractants
exist, birds will be a problem.
In most situations, a
wildlife biologist trained in bird hazard assessment
should be selected to conduct a thorough ecological
study of the airport and its vicinity. The study should
determine what species of birds are involved, what
attracts them, abundance and peak use periods and
special hazard zones. It should also include control
recommendations to reduce the frequency of bird
occurrence at the airport.
Several habitat management practices can make
an airport less attractive to birds. These include
eliminating standing water, removing or thinning trees,
removing brush and managing grass height. Buildings can
be modified to reduce or eliminate roosting or nesting
FAA Order 5200.5A provides
guidelines for the establishment, elimination, or
monitoring of landfills, open dumps, or waste disposal
sites on or in the vicinity of airports.
Frightening is a reliable and expeditious means of
repelling birds. Frightening programs, however, provide
only temporary relief and require constant monitoring.
An early priority in
reducing bird hazards is to establish a bird dispersal
patrol team to harass and scare birds and provide
immediate protection for aircraft within the airport
perimeter. The patrol team must consist of highly
motivated and knowledgeable personnel with adequate
equipment, such as radio-equipped vehicles, shotguns,
and frightening devices consisting of bird distress
calls, live ammunition, and pyrotechnic devices
(automatic gas exploders, shellcrackers, and racket
bombs). Patrol personnel must be trained in bird
identification and dispersal methods. Clear
communication between the patrol team and the control
tower is essential.
Birds react to unfamiliar
sounds and objects. They learn, however, to ignore
sounds and objects that have proven harmless, especially
if they are used often and for long periods of time.
Birds should not be allowed to acclimate to a scare
device through repeated exposure without an associated
adverse effect. The use of shooting to reinforce
frightening techniques can be effective and should occur
simultaneously with the scare devices often enough to
maintain fear in the birds. In most cases, an integrated
approach that incorporates several frightening devices
will produce the best results.
The shellcracker fires a
projectile from a 12-gauge shotgun. It travels up to 100
yards (90 m) and explodes with a loud noise and a flash.
Noise bombs are similar and can supplement shellcrackers,
but their range is much shorter. Racket bombs are
propelled by a special pistol and travel approximately
100 yards (90 m); they do not explode.
Shellcrackers and racket
bombs may lose their effectiveness when used frequently.
It may be necessary to use live ammunition to kill an
occasional bird. Remaining birds then become more
responsive to the noise devices. Remember that a permit
is required to take protected species.
Distress calls are sounds
emitted by birds under conditions of stress. The calls
can be recorded on tape cassettes and played through a
loudspeaker located on the patrol vehicle. Distress
calls supplement shellcrackers and noise bombs.
Automatic exploders or gas
cannons, operated by acetylene, propane, or LP gas,
produce a noise louder than a shotgun blast. Exploders
can be set up and left to operate continuously, but for
best results, the exploders should be operated for
limited periods of time only, unless birds are moving
into the airport. Exploders should be moved periodically
so that the birds do not become accustomed to the
Research has been conducted on the efficacy of
methyl anthranilate (ReJeXiT, Peter Vogt, PMC Corp.,
pers. commun.) for repelling gulls and waterfowl from
standing pools of wtaer on airport runways. Results are
promising and registration of ReJeX-iT by the
Environmental Protection Agency is currently pending.
Methyl anthranilate is a grape-flavored food additive.
Shooting birds with shotguns or rifles can be a
highly selective and useful form of hazard control under
certain conditions. Federal, state, and possibly
municipal permits are required. Shooting has been used
to reduce hazards caused by birds that habitually fly
over airport runways. Caution must be used so that
shooting does not disturb nontarget species. Shooting is
not practical or desirable as a method for reducing
large numbers of birds.
USDA-APHIS-ADC provides technical and operational
assistance to airports on all aspects of wildlife hazard
management, including workshops on bird hazard
management, conducting environmental assessments, and
developing airport wildlife hazard management plans.
I thank James Forbes,
USDA-APHIS-ADC, and Eugene LeBoeuf, Federal Aviation
Administration, for reviewing the manuscript.
For Additional Information
Arnold, K. A. 1981. Environmental control of birds.
Pages 499-505 in D. Pimentel, ed. CRC handbook of pest
management in agriculture, vol. 1. CRC Press, Boca
Raton, Florida. 597 pp.
Brough, T., and C. J.
Bridgman. 1980. An evaluation of long grass as a bird
deterrent on British airfields. J. Appl. Ecol.
Pearson, Erwin W. 1967.
Birds and airports. Proc. Vertebr. Pest Conf. 3:79-86.
Solman, Victor E. F. 1981.
Birds and aviation. Environ. Conserv. 8:45-51.
Thompson, Richard L. 1983.
Bird hazards at airports. Proc. Eastern Wildl. Damage
Control Conf. 1:331.
Scott E. Hygnstrom; Robert
M. Timm; Gary E. Larson
PREVENTION AND CONTROL OF
WILDLIFE DAMAGE — 1994
Division Institute of Agriculture and Natural Resources
University of Nebraska -Lincoln
United States Department
of Agriculture Animal and Plant Health Inspection
Service Animal Damage Control
Great Plains Agricultural
Council Wildlife Committee