Content uploaded by Eric A. Tillman
Author content
All content in this area was uploaded by Eric A. Tillman on Dec 17, 2013
Content may be subject to copyright.
82
ALIEN BIRDS IN NORTH AMERICA – CHALLENGES FOR WILDLIFE MANAGERS
MICHAEL L. AVERY, USDA, APHIS, Wildlife Services, National Wildlife Research Center,
Gainesville, FL, USA
ERIC A. TILLMAN, USDA, APHIS, Wildlife Services, National Wildlife Research Center,
Gainesville, FL, USA
Abstract: In Executive Order 13112 “Invasive Species”, an alien species is defined as one “that
is not native” to a particular ecosystem. In North America today, there are nearly 100 alien bird
species with self-sustaining populations. These include numerous game birds (primarily
gallinaceous birds) and escaped pet birds (primarily psittacine species). Others, such as house
sparrows (Passer domesticus), European starlings (Sturnus vulgaris), and mute swan (Cygnus
olor), were originally introduced for aesthetic reasons or to control agricultural insect pests. The
establishment of alien bird populations through purposeful or accidental introductions has
resulted in numerous problems including crop damage, transmission of disease, adverse impacts
to native species, and aircraft safety concerns. The estimated cost associated with alien bird
species in North America approaches $2 billion annually. Although many alien bird species
apparently cause minimal or no harm, others are considered persistent and destructive pest
species. The challenge for wildlife managers often is one of public opinion and education rather
than identifying effective management and control strategies. For many bird damage situations,
techniques currently exist for addressing the specific problem, and ongoing research is providing
new tools. Many times, however, the will of the public overrides the scientific and economic
need to manage aggressively to reduce detrimental alien bird populations. Specific examples of
this dilemma for wildlife managers are provided by case studies featuring monk parakeets
(Myiopsitta monachus), and mute swan.
Key words: alien species, introduction, invasive species, native species
Proceedings of the 11
th
Wildlife Damage
Management Conference. (D.L. Nolte, K.A.
Fagerstone, Eds). 2005
INTRODUCTION
By some estimates, as many as 97
non-native bird species have self-sustaining
populations in the United States (Temple
1992). Many of these species are now
fixtures in the avifauna of the country. The
ring-necked pheasant (Phasianus colchicus)
and gray partridge (Perdix perdix) are
widely hunted species. The European
starling (Sturnus vulgaris), rock pigeon
(Columba livia), and house sparrow (Passer
domesticus) regularly occur in large
numbers in urban and agricultural locales
throughout the country. Other species such
as the monk parakeet (Myiopsitta monachus)
in Florida, the red-crowned parrot (Amazona
viridigenalis) in California, and the Eurasian
tree sparrow (Passer montanus) in Missouri
are common locally but currently are
geographically restricted.
Application of consistent
nomenclature clarifies a non-native species’
origin and impact; we will apply definitions
from Executive Order 13112 “Invasive
Species” published in February 1999. An
“alien species” is a species not native to the
83
ecosystem under consideration. An
“invasive species” is an alien species whose
introduction is likely to cause harm
(emphasis added), either economically,
environmentally, or to human health. An
“introduction” is the placement of a species
into an ecosystem as a result of human
activity. A “native species” is one that
occurs in a particular ecosystem not as a
result of an introduction.
Thus, while all species mentioned in
the first paragraph are alien species, they
might not all be invasive species. It is not
clear what harm species such as the gray
partridge or the red-crowned parrot are
doing. Further, species that have exhibited
range expansions in recent time unaided by
human intervention are deemed native.
These include the cattle egret (Bubulcus
ibis), originally an Old World species that
reached South America from Africa and
then spread northward (Telfair 1994).
Breeding was recorded in Florida in 1953
(Kale and Maehr 1990) and cattle egrets are
now widely distributed throughout the US.
The shiny cowbird (Molothrus bonariensis)
arrived unaided to the Florida Keys in 1985
from the Caribbean, is now considered to be
a permanent resident in south Florida, and
continues to spread north and west (Lowther
and Post 1999).
Management of alien species should
focus on those considered invasive, that is
those whose presence is causing, or likely
will cause, harm. The major invasive bird
species that are of management concern in
the continental United States are the house
sparrow, rock pigeon, and European starling.
These species are so entrenched in their
adopted home that it seems unthinkable to
be without them. Their success is
attributable to their opportunistic nature and
ability to exploit human-altered
environments for food, roost sites, and
nesting. They exhibit basically a parasitic
lifestyle in that they exist on anthropogenic
resources and provide little if any benefit in
return. In commensal associations,
members of one species assist the foraging
of another, but incur no significant costs and
receive no benefits. These species,
however, generate substantial costs in a
number of areas and highlight the threats
from introduction of alien species.
Impacts to Native Species
Numerous examples exist of the
negative impact invasive species have on
native birds. European starlings compete
aggressively for nesting cavities, often to the
detriment of native birds (Kerpez and Smith
1990). Similarly, house sparrows will
supplant and even kill native species
attempting to use nest boxes (Gowaty 1984,
Radunzel et al. 1997). Mute swan adversely
affect habitat for native waterfowl species
and even displace colonial nesting
waterbirds (Conover and Kania 1994,
Maryland Department of Natural Resources
2003). In Hawaii, alien birds have
facilitated the spread of mosquito-borne
diseases that have decimated native bird
populations (Warner 1968).
Agricultural Damage
The European starling is known for
its propensity to damage fruit crops,
sprouted seeds, and livestock feedlots
(Dolbeer et al. 1978, Somers and Morris
2002). Ring-necked pheasant damage to
sprouting corn can be locally severe (Besser
and Knittle 1976).
Nuisance Roosts and Structural Damage
Starlings are major components of
winter blackbird roosts which are noisy,
smelly and generally not aesthetically
pleasing (Dolbeer et al. 1978, Mott 1980).
Urban house sparrows, starlings and rock
pigeons constantly foul structures and
property with droppings. Monk parakeets
offer unique challenges through their habit
84
of constructing large nests of sticks on
electric utility facilities (Avery et al. 2002,
Tillman et al. 2004). Wet nest material
causes short circuits which in turn damage
facilities and create economic losses for the
companies and their customers.
Human Health and Safety
Histoplasmosis is a serious
respiratory ailment caused by fungal spores
produced in excrement under large starling-
blackbird roosts (D'Alessio et al. 1965,
Stickley and Weeks 1985). This, however,
is just one of over 60 transmissible diseases
known to occur in starlings, house sparrows
and rock pigeons (Weber 1979). Fecal
contamination from these 3 species is a
major concern in food production and
storage facilities (Baur and Jackson 1982).
Since 1990, European starlings and rock
pigeons have been involved in
approximately 2000 aircraft strike incidents
that resulted in losses of approximately $4.5
million (Cleary et al. 2003).
Pimentel et al. (2000) estimated that
costs associated with invasive bird species,
principally pigeons and starlings, approach
$2 billion annually. Unfortunately, the
origin of this cost estimate is not very well
documented. Most of it is based on a cost of
$9/bird derived from a report on pigeon
control operations in Basel, Switzerland
(Haag-Wackernagel 1995). Regardless of
the exact monetary figure, it is obvious that
pigeons, starlings, house sparrows and other
alien bird species are responsible for
substantial costs due to a variety of impacts.
Although the European starling and the
house sparrow are among the most common
and most widespread breeding birds in the
US, each species has experienced a general
population decline since the 1960’s (Figure
1). The decline in house sparrow
populations in the US mirrors a similar trend
in the UK which has yet to be satisfactorily
explained (Duncan 1996, Summers-Smith
2003).
Wildlife professionals, facility
managers, and private citizens have
numerous tools and techniques with which
to combat the impacts of house sparrows,
starlings and pigeons (Hyngstrom et al.
1994). The list of visual, acoustic and
chemical methods will not be reviewed
again here. Instead we want to highlight 2
case studies of alien bird species that
represent different challenges for wildlife
managers.
Figure 1. Population trends of European
starling (EUST) and the house sparrow
(HOSP) throughout the USA as determined
by the Breeding Bird Survey, 1966-2004.
Data are from Sauer et al. 2005.
CASE STUDIES
Mute Swan
This large, attractive Eurasian
species was released by private individuals
85
in New York prior to 1900, but there is no
record of when the initial introduction
actually occurred (Long 1981). The species
now occurs from Massachusetts south to
Virginia, as well as in Michigan, Oregon
and several other states. The population
trend for this species in the US, as judged by
the Breeding Bird Survey, has been steadily
upward (Figure 2; Sauer et al. 2005). The
recent trend in Maryland has been even
more dramatic (Figure 2). In Maryland, 5
birds escaped in 1962, and the population
now approaches 4,000 (Maryland
Department of Natural Resources 2003).
Figure 2. Population trends of the mute swan
throughout the USA and in Maryland as
determined by the Breeding Bird Survey,
1966-2004. Data are from Sauer et al. 2005.
Despite their aesthetic appeal, mute
swans pose a series of concerns (Maryland
Department of Natural Resources 2003).
They sometimes threaten or directly attack
people who get too close to their nest or
young. Aggressive behavior exhibited by
these large birds can pose a safety risk,
especially to small children. Mute swans
consume enormous quantities of submerged
aquatic vegetation. It is estimated that 4,000
mute swan could annually consume about
12% of the submerged aquatic vegetation
biomass in the Chesapeake Bay. Submerged
aquatic vegetation is critical to the health
and well being of a myriad of Bay
organisms. Grazing of this resource by mute
swans reduces the capacity of the remaining
submerged aquatic vegetation beds to
support wintering waterfowl and other fish
and wildlife populations. Mute swans
occupy and defend relatively large territories
of wetland habitat during nesting, brood
rearing and foraging, and thus compete with
native birds for habitat. They displace
native waterfowl from breeding and staging
habitats and have been reported to attack,
injure, or kill other wetland birds. Mute
swans can reach 1 m under water to graze
vegetation, and they are present year-round
unlike native tundra swans (Cygnus
columbianus) which overwinter in the
Chesapeake Bay. Thus, the mute swans’
impact on native submerged vegetation is
extensive, both temporally and spatially. In
the early 1990’s, 600-1,000 mute swans
established a loafing area on oyster shell
bars and beaches used as nesting sites by
black skimmers (Rynchops niger) and least
terns (Sterna antillarum). This resulted in
abandonment of the site by these threatened
waterbird species. The destabilizing effects
of mute swan on Chesapeake Bay plant and
animal communities place it in the category
of a “strongly interacting nonindigenous
species” and signals the need for prompt and
effective management actions (Heiman
2005, Soulé et al. 2005). In 2003, the
Maryland DNR initiated a program of mute
swan population control that included egg
addling and culling adults. This
management program barely got underway
86
before it was halted through a legal
challenge that resulted in a Federal court
ruling that declared the mute swan protected
under the Migratory Bird Treaty Act
(MBTA). This ruling, in turn, lead to the
passage of the Migratory Bird Treaty
Reform Act (MBTRA) of 2004. As a
consequence of the new legislation, the US
Fish and Wildlife Service published new
guidelines that specifically removed the
mute swan and dozens of other alien bird
species from Federal protection under the
MBTA. In the wake of these new
developments, the Maryland DNR planned
to resume a large-scale egg addling program
in April 2005. The mute swan management
program is again on hold, however, because
the Humane Society of the United States and
others recently challenged the MBTRA in
Federal court.
Monk Parakeet
This South American species has a
reputation for causing substantial crop
damage in its native range (Mott 1973).
Thus, in the early 1970’s when free-flying
parakeet populations started showing up in
greater and greater numbers, US wildlife
and agriculture officials became alarmed at
the potential crop damage that could occur
here. In response to that concern, a parakeet
eradication effort was initiated in 1973
under the direction of the US Fish and
Wildlife Service (Neidermyer and Hickey
1977). The 3-year effort resulted in 163
parakeets being killed, mostly by shooting.
Since then, the nationwide population has
grown exponentially (van Bael and Pruett-
Jones 1996).
Although monk parakeets do cause
some local crop damage (Tillman et al.
2001), in the US, no widespread agricultural
impacts have yet emerged. Instead, the
parakeets have become problems for the
electric utility industry because of their habit
of constructing large nests of sticks and
branches on utility poles, transmission line
support towers, and electric substations
(Avery et al. 2002). Wet nest material then
causes short circuits and power outages.
Research to alleviate this problem is
ongoing. To date, trapping birds at their
nest followed by removal of the nest is the
most effective technique for coping with
localized problem nests on a short-term
basis (Tillman et al. 2004). Application of a
hand-held red laser is an effective scare
tactic to dislodge parakeets temporarily from
their nest sites. Despite repeated use of the
laser, however, the birds do not stay away
(Avery et al. 2002).
Figure 3. Population trend of the monk
parakeet throughout the USA as determined
by data from the Christmas Bird Count,
1975-2003. Values for the graph were
obtained online at: http://www.audubon.org
/bird/cbc/hr/index.html
Ultimately some form of population
reduction will probably have to be
implemented to slow the expansion of the
species because parakeet populations show
no sign of leveling off (Figure 3) (van Bael
and Pruett-Jones 1996). Factors that limit
many bird populations such as predation,
food, and availability of nest sites are not
operative because of the parakeet’s ability to
exploit the abundance of resources provided
by humans. This suggests that current
problems will only get worse without
intervention. Lethal control is unpopular,
87
however, as many people enjoy the sight of
these birds at their backyard feeders or in
community parks (Spreyer 1994). An
alternative that might prove feasible is the
application of a chemosterilant that would
reduce reproductive output but not kill the
birds (Avery et al. 2005).
MANAGEMENT IMPLICATIONS
For the most part, current methods
are adequate to address problems attributed
to invasive bird species. The major issue is
that wildlife managers are often not free to
apply the most effective techniques to solve
problems caused by invasive species. The
constraint is particularly prominent in
situations that involve lethal control
measures. Public attitudes which often
become manifested in actual or implied legal
challenges or lawsuits can seriously delay or
even prevent implementation of the most
appropriate management actions. Concerted
public education efforts can sometimes
overcome attitudes against management of
wildlife populations, and such efforts are
certainly desirable when lethal control
measures are contemplated. Effective
education presupposes that adequate
scientific data exist upon which to base a
sound management program. If such data
are not available then attempts to justify a
proposed plan that involves population
reduction will likely fail. It will be important
to have reliable information on the status of
the population targeted for reduction as well
as thorough documentation of the adverse
impacts the birds are having.
A contrary view is offered by
Simberloff (2003) who argues for swift and
decisive action to eradicate invasives before
they become major problems. This “quick
and dirty” strategy is necessary because
during the time that biologists and wildlife
managers amass data on the population and
the effects it is having, the animals multiply
or disperse and the problems become harder
to address successfully. While this approach
might be possible when incipient invasive
populations are small and isolated, it has
limited utility for control of established
invasive populations. In addition,
Simberloff does not consider the role that
public opinion would play in
implementation of his strategy. A “quick
and dirty” response, unless conducted
surreptitiously, is likely to attract attention.
If the proper groundwork for the operation
has not been laid, subsequent public reaction
will likely be negative which will
complicate more comprehensive
management efforts. More stringent laws
and beefed-up enforcement of existing
regulations are necessary to preventing
establishment of new invasive bird
populations.
For managing existing invasive bird
populations, increased public appreciation of
the need for effective control measures is
necessary. This can best be achieved
through science-based public awareness and
education programs (Temple 1992).
LITERATURE CITED
AVERY, M.L., E.C. GREINER, J.R. LINDSAY, J.R.
NEWMAN, AND S. PRUETT-JONES.
2002. Monk parakeet management at
electric utility facilities in south Florida.
Proceedings of the Vertebrate Pest
Conference 20:140-145.
_____,
J.R. LINDSAY, J.R. NEWMAN, S. PRUETT-
J
ONES, AND E.A. TILLMAN. 2005.
Reducing monk parakeet impacts to
electric utility facilities in south Florida.
Advances in Vertebrate Pest
Management. In press.
B
AUR, F.J., AND W.B. JACKSON, editors. 1982.
Bird control in food plants. American
Association of Cereal Chemists. St.
Paul, MN, USA.
B
ESSER, J.F., AND C.E. KNITTLE. 1976.
Mesurol 50 percent HBT for protecting
sprouting corn from pheasants in Iowa
and South Dakota. Proceedings of the
Bird Control Seminar 7:225-227.
88
CLEARY, E.C., R.A. DOLBEER, AND S.E.
WRIGHT. 2003. Wildlife strikes to civil
aircraft in the United States 1990-2002.
Federal Aviation Administration
National Wildlife Strike Database Serial
Report 9.
C
ONOVER, M.R., AND G.S. KANIA. 1994.
Impact of interspecific aggression and
herbivory by mute swans on native
waterfowl and aquatic vegetation in
New England. Auk 111:744-748.
D'A
LESSIO, D.J., R.H. HEEREN, S.L.
HENDRICKS, P. OGILVIE, AND M.L.
FURCOLOW. 1965. A starling roost as
the source of urban epidemic
histoplasmosis in an area of low
incidence. American Review of
Respiratory Disease 92:725-731.
D
OLBEER, R.A., P.P. WORONECKI, A.R.
STICKLEY, JR., AND S.B. WHITE. 1978.
Agricultural impact of a winter
population of blackbirds and starlings.
Wilson Bulletin 90:31-44.
D
UNCAN, R.A. 1996. House sparrow (Passer
domesticus) trends in coastal northwest
Florida-Alabama based on Christmas
bird count data. Alabama Birdlife 42:1-
2.
G
OWATY, P.A. 1984. House sparrows kill
eastern bluebirds. Journal of Field
Ornithology. 55:378-380.
H
AAG-WACKERNAGEL, D. 1995. Regulation of
the street pigeon in Basel. Wildlife
Society Bulletin 23:256-260.
H
EIMAN, K. 2005. Strongly interacting
nonindigenous species. BioScience
55:548.
H
YGNSTROM, S.E., R.M. TIMM, AND G.E.
LARSON, editors. 1994. Prevention and
control of wildlife damage. University
of Nebraska, Lincoln, NE, USA.
K
ALE, H.W. II, AND D.S. MAEHR. 1990.
Florida’s birds, a handbook and
reference. Pineapple Press, Sarasota,
FL, USA.
K
ERPEZ, T.A., AND N.S. SMITH. 1990.
Competition between European starlings
and native woodpeckers for nest cavities
in saguaros. Auk 107:367-375.
L
ONG, J.L. 1981. Introduced birds of the world.
Universe Books. New York, NY, USA.
L
OWTHER, P., AND W. POST. 1999. Shiny
cowbird (Molothrus bonariensis). The
birds of North America, No. 399. The
Academy of Natural Sciences,
Philadelphia, PA and The American
Ornithologists’ Union, Washington,
D.C., USA.
Maryland Department of Natural Resources.
2003. Mute swans in Maryland: A
statewide management plan. Wildlife
and Heritage Service. On-line access at:
www.dnr.state.md.us/wildlife/msfinaltoc.
html
M
OTT, D 1973. Monk parakeet damage to
crops in Uruguay and its control.
Proceedings of the Bird Control Seminar
6:79-81.
_____. 1980. Dispersing blackbirds and
starlings from objectionable roost sites.
Proceedings of the Vertebrate Pest
Conference 9:38-42.
N
EIDERMYER, W.J., AND J.J. HICKEY. 1977.
The monk parakeet in the United States,
1970-1975. American Birds 31:273-278.
P
IMENTEL, D., L. LACH, R. ZUNIGA, AND D.
MORRISON. 2000. Environmental and
economic costs of nonindigenous
species in the United States. BioScience
50:53-65.
R
ADUNZEL, L.A., D.M. MUSCHITZ, V.M.
BAULDRY, AND P. ARCESE. 1997. A
long-term study of the breeding success
of eastern bluebirds by year and cavity
type. Journal of Field Ornithology 68:7-
18.
S
AUER, J.R., J.E. HINES, AND J. FALLON. 2005.
The North American breeding bird
survey, results and analysis 1966 - 2004.
Version 2005.2. USGS Patuxent
Wildlife Research Center, Laurel, MD,
USA.
S
IMBERLOFF, D. 2003. How much information
on population biology is needed to
manage introduced species?
Conservation Biology 17:83-92.
S
OMERS, C.M. AND R.D. MORRIS. 2002. Birds
and wine grapes: Foraging activity
causes small-scale damage patterns in
single vineyards. Journal of Applied
Ecology 39:511-523.
89
SOULÉ, M.E., J.A. ESTES, B. MILLER, AND D.L.
HONNOLD. 2005. Strongly interacting
species: Conservation policy,
management, and ethics. BioScience
55:168-176.
S
PREYER, M. 1994. Mayor Washington’s birds:
The legendary monk parakeets of
Chicago’s Hyde Park. Birder’s World
8:40-43.
S
TICKLEY, A.R. JR., AND R.J. WEEKS. 1985.
Histoplasmosis and its impact on
blackbird/starling roost management.
Proceedings of the Eastern Wildlife
Damage Control Conference 2:163-171.
S
UMMERS-SMITH, J.D. 2003. The decline of
the house sparrow: A review. British
Birds 96:439-446.
T
ELFAIR, R.C. II. 1994. Cattle egret (Bubulcus
ibis). The birds of North America, No.
113. The Academy of Natural Sciences,
Philedelphia, PA, and The American
Ornithologists’ Union, Washington,
D.C., USA.
T
EMPLE, S.A. 1992. Exotic birds: A growing
problem with no easy solution. Auk
109:395-397.
T
ILLMAN, E.A., A.C. GENCHI J.R. LINDSAY,
J.R. NEWMAN, AND M. L. AVERY.
2004. Evaluation of trapping to reduce
monk parakeet populations at electric
utility facilities. Proceedings of the
Vertebrate Pest Conference 21:126-129.
_____, A.
VAN DOORN, AND M.L. AVERY.
2001. Bird damage to tropical fruit in
south Florida. Proceedings of the
Eastern Wildlife Damage Management
Conference 9:47-59.
V
AN BAEL, S., AND S. PRUETT-JONES. 1996.
Exponential population growth of monk
parakeet in the United States. Wilson
Bulletin 108:584-588.
W
ARNER, R.E. 1968. The role of introduced
diseases in the extinction of the endemic
Hawaiian avifauna. Condor 70:101-
120.
W
EBER, W.J. 1979. Health hazards from
pigeons, starlings and English sparrows.
Thomson Publications. Fresno, CA,
USA.
