ArticlePDF Available

Evaluating the Effectiveness of Select Visual Signals to Prevent Bird-window Collisions



Billions of birds are estimated to be killed striking clear and reflective windows worldwide, and conservation, ethical, and legal reasons justify preventing this unintended human-associated avian mortality. Field experiments reveal that to be effective, UV signals used to prevent bird-window collisions must minimally reflect 20–40% from 300–400 nm. Field experiments reveal 3.175 mm parachute cord hung in front of clear and reflective windows separated by 10.8 cm and 8.9 cm are effective bird-window collision preventive methods. The results of the parachute cord experiment and those of previous studies support the importance of applying collision prevention methods to the outside window surface reflecting the facing habitat and sky. Comparison of field and tunnel testing experimental protocols to evaluate bird-window collision preventive methods suggest that tunnel testing is useful for initial assessment but not as a definitive measure of effectiveness.
Published by the
Wilson Ornithological Society
Evaluating the Effectiveness of Select Visual Signals to Prevent
Bird-window Collisions
Daniel Klem Jr.
and Peter G. Saenger
The Wilson Journal of Ornithology 125(2):406–411, 2013
Evaluating the Effectiveness of Select Visual Signals to Prevent
Bird-window Collisions
Daniel Klem Jr.
and Peter G. Saenger
ABSTRACT.—Billions of birds are estimated to be
killed striking clear and reflective windows worldwide,
and conservation, ethical, and legal reasons justify
preventing this unintended human-associated avian
mortality. Field experiments reveal that to be effective,
UV signals used to prevent bird-window collisions must
minimally reflect 20–40%from 300–400 nm. Field
experiments reveal 3.175 mm parachute cord hung in
front of clear and reflective windows separated by
10.8 cm and 8.9 cm are effective bird-window collision
preventive methods. The results of the parachute cord
experiment and those of previous studies support the
importance of applying collision prevention methods to
the outside window surface reflecting the facing habitat
and sky. Comparison of field and tunnel testing
experimental protocols to evaluate bird-window colli-
Acopian Center for Ornithology, Department of Biol-
ogy, Muhlenberg College, Allentown, PA 18104, USA.
Corresponding author; e-mail:
sion preventive methods suggest that tunnel testing is
useful for initial assessment but not as a definitive
measure of effectiveness. Received 6 January 2012.
Accepted 19 December 2012.
Key words: collision prevention, testing, ultraviolet
(UV) signals, visual information, windows.
Except for habitat destruction, the casualties
attributable to bird-window collisions total in the
billions worldwide and are estimated to be greater
than any other human-associated source of avian
mortality (Klem 1990, 2009a; Hager et al. 2008).
More accurate estimates of birds killed striking
windows and the implications of this and other
human-caused avian mortality are currently under
study for management of specific species and birds
in general (Arnold and Zink 2011, Bayne et al.
2012, Loss et al. 2012). Minimally, preventing
these unintended and unwanted deaths has ethical
and moral value, and a legal international treaty
obligation, implemented in the United States by
The Migratory Bird Treaty Act (MBTA) of 1918
and the Endangered Species Act of 1973, as
respectively amended (Bean 1983, Corcoran 1999).
Several review papers document extensive
published evidence in the ornithological literature
that birds behave as if clear and reflective
windows are invisible to them (Erickson et al.
2001; Klem 2006, 2009a, 2010; Drewitt and
Langston 2008). Visual patterns composed of
uniformly spaced elements covering an entire
pane are known to transform windows into
obstacles that birds see and avoid (Klem 1990,
2009b). To retain the utility of unobstructed
viewing, the seemingly most acceptable solution
to protect birds from windows is to incorporate
ultraviolet (UV) signals into visual patterns that
birds see and humans do not (Klem 2009b).
We evaluated the strength and wavelength of
UV signals necessary to prevent bird-window
collisions using field experiments, and we com-
pare these results to those evaluating the same
signals using a flight tunnel. We also reexamine
and evaluate the spacing of opaque elements
making up a pattern uniformly covering a window
to prevent collisions. Specifically, we tested: (1) a
commercial window manufactured for new and
remodeled construction named ORNILUX Mika-
do that offers a UV signal for the purpose of
preventing bird-window collisions, and (2) two
versions of a commercial window product named
Acopian BirdSavers that uses vertically hung
opaque parachute cords. We use our findings
and previously published results to comment on
the relative importance of using field experiments
as a final test in evaluating bird-window collision
prevention methods and the importance of apply-
ing preventive methods to the surface of a window
facing the outside environment.
Our field experiments were conducted on a
2-ha area of mowed pasture bordered by second
growth deciduous forest and shrubs in Hennings-
ville, Berks County, Pennsylvania, USA (40u279
530N, 075u409070W). The basic design of the
two field experiments was the same as reported
previously (Klem 1989, 1990, 2009b), consisting
of wood-framed picture windows, simulating
those in houses. All windows were placed in the
same habitat facing the same direction along the
edge of trees and open field (Klem 1989: fig. 1).
Each window measured 1.2 m wide 30.9 m high,
and was mounted 1.2 m above ground. Plastic
mesh trays were placed under each window to
catch casualties. Three window units were used in
the first experiment and four in the second; all
windows in both experiments were separated by
2.4 m. Simulating a feeding station at a commer-
cial building or residential home, a single
platform feeder measuring 30.5 cm on a side
and 1.2 m above ground mounted on crossed
wooden-legs were centered and placed 10 m in
front of each window. Feed consisted of a 1:1
mixture of black-oil sunflower and white proso
millet. All feeders were kept full throughout each
experiment. Controls and treatments were ran-
domly assigned daily to a new position with the
exception that no treatment or control was
permitted in the same position on consecutive
days. Windows were checked each day 30 min
after first light and checked and changed daily
30 min before last light. In an attempt to observe
active avoidance of treatments, all windows in the
second experiment were monitored during multi-
ple-hour continuous periods totaling 63.5 hrs over
16 days (22, 26 Feb, 18, 21, 22, 26, 27, 28, 29
Mar, and 4, 8, 9, 11, 15, 18, 22 Apr 2011). The
observer was positioned 20 m from and in the
middle of the window units in a camouflaged
blind behind the platform feeders. The flights of
individual birds moving from the tray feeders
toward the windows were recorded and assessed
as an active avoidance if a bird changed direction
and passed around or over a window.
The parameter measured in the experiments
was the number of detectable bird strikes. A strike
was recorded when either dead or injured birds
were found beneath a window, or when fluid or a
blood smear, feather, or body smudge was found
on the glass. As in previous studies of similar
design (Klem 1989, 1990, 2009b; Klem et al.
2004), the data are likely to be incomplete and
conservative because some strikes may not have
left evidence of a collision. Additionally, preda-
tors and scavengers are known to remove some
injured or dead birds (Klem 1981, 2009b; Klem
et al. 2004; Hager et al. 2012).
Our field design can accommodate a maximum
of four window units; two experiments were
required to test the effectiveness of the preventive
methods studied. The first experiment was
conducted over 75 days from 3 October–18
December 2010, and compared clear (see-
through) and reflective (mirrored) glass controls
and an ORNILUX Mikado window offering UV
signals as a see-through pane simulating installa-
tion in a corridor between buildings, as a noise
barrier along roadways, or as glass walls around
zoo enclosures or building atria.
The second experiment was conducted over
68 days from 9 February–22 April 2011, and
tested the clear glass control, ORNILUX Mikado
pane covering a recessed non-reflective black
wooden board simulating a window that covered a
darkened room, and two vertically striped spacing
variations of preventive treatments known as
Acopian BirdSavers: (1) a clear glass pane
covered with 3.175 mm parachute cord spaced
10.8 cm from the center of one cord to the center
of the next, and (2) a reflective (mirror) glass pane
covered with 3.175 mm parachute cord spaced
8.9 cm from the center of one cord to the center of
the next.
CPFilms, Solutia, Inc. measured reflected UV
strength and wavelength for a sample of ORNI-
LUX Mikado and for the conventional clear and
reflective float glass controls using a Cary 5000
Spectrophotometer. ORNILUX Mikado reflected
7%UV from 300–380 nm, and 7–22%from 380–
400 nm. The clear and reflected glass controls
uniformly reflected 13%UV or less over 300–
400 nm. The parachute cord reflected 8%UV or
less over 300–400 nm; it was olive green and non-
reflective to the human eye.
Our experimental protocol was approved by our
Institutional Animal Care and Use Committee
(IACUC), and birds killed during the study were
salvaged under state and federal permits. Chi-
square goodness-of-fit was used to compare the
frequency of strikes among treatments in the two
experiments, and test results were considered
statistically significant when P,0.05 (Siegel
1956). We used SPSS (SPSS 2010) for all
statistical analyses of the experiments.
A total of 116 strikes were recorded in the first
experiment; 19 (16%) were fatal. The number of
strikes did not differ significantly across all
treatments with 32 (28%) at the clear glass control,
43 (37%) at the reflective glass control, and
41 (35%) at the ORNILUX Mikado (x
df 52, P50.41). The number of fatal strikes
differed significantly across all treatments with 2
(10%) at the clear glass control, 6 (32%) at the
reflective glass control, and 11 (58%) at the
ORNILUX Mikado (x
56.421, df 52, P5
0.040). Species numbers and treatment at which
fatalities occurred were: two Dark-eyed Juncos
(Junco hyemalis) at the clear glass control, two
Black-capped Chickadees (Poecile atricapillus),
three Northern Cardinals (Cardinalis cardinalis),
and one House Finch (Carpodacus mexicanus)at
the reflective glass control, and two Black-capped
Chickadees, one Ruby-crowned Kinglet (Regulus
calendula), one Hermit Thrush (Catharus gutta-
tus), one Gray Catbird (Dumetella carolinensis),
three Northern Cardinals, two Dark-eyed Juncos,
and one American Goldfinch (Spinus tristis) at the
One hundred and twelve strikes were recorded
in the second experiment; 22 (27%) were fatal.
The total number of strikes differed significantly
across all windows, with 69 (62%) at the clear
glass control, 31 (28%) at ORNILUX over dark
interior, 7 (6%) at parachute cords spaced 10.8 cm
apart covering clear pane, and 5 (4%) at parachute
cords spaced 8.9 cm apart covering reflective
pane (x
595.00, df 53, P,0.001). The
number of fatal strikes differed significantly
across all treatments with 1 (5%) fatality of
Northern Cardinal at the clear pane covered by
parachute cords spaced 10.8 cm apart, and all 21
(95%) other fatalities at the clear glass control
that included: one Mourning Dove (Zenaida
macroura), one Black-capped Chickadee, three
Northern Cardinals, one Purple Finch (Carpoda-
cus purpureus), one White-throated Sparrow
(Zonotrichia albicollis), and 14 Dark-eyed Juncos
558.364, df 53, P,0.001).
Flight paths of 44 individual birds flying from
bird feeders toward the experimental windows
were recorded to determine avoidance perfor-
mance. Of six individuals flying toward the clear
glass control, four (67%) moved to avoid and two
(33%) hit the window. Of 16 individuals flying
toward the ONILUX over dark interior, 12 (75%)
moved to avoid and four (25%) hit the window.
Of 12 individuals flying toward the parachute
cords spaced 10.8 cm apart covering the clear
pane, 11 (92%) moved to avoid and one (8%) hit
the window. Of 10 individuals flying toward the
parachute cords spaced 8.9 cm apart covering the
reflective pane, all 10 (100%) moved to avoid the
Several studies document evidence that birds
perceive UV wavelengths from approximately
300–400 nm (Burkhardt 1982, Bennett and
Cuthill 1994, Vitala et al. 1995, Bennett et al.
1996, Hunt et al. 1998), and although Martin
(2011) questioned static UV signals as a
collision deterrent, external films consisting of
contrasting UV-absorbing and UV-reflecting
patterns applied to sheet glass have been
effective in deterring bird-window collisions
(Klem 2009b). The use of UV signals to deter
bird-window collisions is arguably the most
practical solution because they preserve the
properties that humans expect and enjoy from
sheet glass while seemingly transforming clear
and reflective panes into obstacles that birds see
and avoid. External films can be used to retrofit
existing panes to render them bird-safe, but
uniquely manufactured sheet glass with UV
coating (glazing) patterns to be used in new and
remodeled construction will be required for a
long-term solution to protect birds from the
harmful effects of window strikes worldwide.
ORNILUX Mikado is a uniquely prepared and
commercially available sheet glass for new and
remodeled construction that claims to use UV
signals to prevent bird strikes. Our first field
experiment revealed that an ORNILUX Mikado
pane installed in see-through settings was more
lethal to birds than conventional clear or
reflective panes. We suggest these results can
be explained by the quality of the UV signal
offered by ORNILUX Mikado to birds. The UV
signal from ORNILUX Mikado reflected a
maximum 7–22%UV from 300–400 nm, reach-
ing above 20%reflection only at 397 nm. By
contrast, previous tests using the same field
experimental design found external films with a
UV-reflecting component of 20–40%over 300–
400 nm to effectively deter bird-window colli-
sions (Klem 2009b). We suggest that the
inability of ORNILUX Mikado installed in a
see-through setting to deter bird strikes is
explained by the lower level of reflected UV
that is available for bird perception, and to offer
an effective collision deterrence the UV-reflect-
ing component of the signal minimally must be
20–40%and be adjacent to contrasting areas of
UV-absorption to further highlight the UV
signal overall.
In our second experiment, ORNILUX Mika-
do covering a darkened interior exhibited a
55%reduced number of strikes compared to the
clear glass control, and this compares to the
58%and 66%deterrence reported for ORNI-
LUX Mikado in a see-through setting using
tunnel testing experiments (American Bird
Conservancy 2011). Tunnel testing experi-
ments consist of releasing birds at one end of
an enclosure where they are attracted to fly to a
brighter lighted opposite end at which they
choose one of two flight paths though an
unobstructed side serving as a control, and the
alternative side containing the collision pre-
vention treatment being tested (Rossler and
Zuna-Kratky 2004, American Bird Conservan-
cy 2011). Why the ORNILUX Mikado window
was more effective in deterring bird strikes
when covering a darkened interior is not
known, and may or may not be associated with
the UV signal offered by the pane.
The frequency of bird strikes at clear and
reflective panes covered by the two spacing
versions of vertically hung parachute cord provide
additional evidence, further validating previous
studies that vertical stripes separated by 10 cm or
less are effective bird-window collision preventive
methods (Klem 1990, 2009b; Rossler and Zuna-
Kratky 2004; American Bird Conservancy 2011).
The observations documenting flight paths of
individual birds toward the window treatments in
the second field experiment further supports the
level of deterrence recorded for ORNILUX
Mikado covering a darkened interior and the two
vertically hanging parachute cord patterns.
The discrepancy in the test results that occurred
using our field experiment compared to tunnel
testing experiments conducted by the American
Bird Conservancy (2011) suggests caution in
relying on tunnel testing as a final assessment of
effectiveness of any bird-window collision pre-
vention method. When comparing the protocol
of field and tunnel testing experiments, tunnel
experiments are markedly not as accurate in
simulating hazardous clear and reflective win-
dows installed in human structures. Components
of tunnel experiments that limit a more accurate
simulation of installed windows include: (1) the
stress of captured individuals of several different
species released to fly within restricted space to
alternative decision areas, (2) controlling illumi-
nation to simulate clear and reflective panes, (3)
netting placed in front of test panes that subjects
can potentially see and thereby influence their
choice, and (4) not being able to control for
variable weather conditions during test periods.
By contrast, our field experimental design far
more accurately simulates installed windows in
commercial and residential buildings, and each
preventive treatment and control are monitored
under the same conditions. Moreover, field
experiments can control for bias of installation
location by randomly moving treatments and
control daily over the experimental period. The
ability to conduct experiments by randomly
moving treatments and controls at existing
structures is extremely difficult and most often
Tunnel experiments are most useful in evalu-
ating several potential preventive options to deter
birds from striking see-through windows. Most
results from tunnel tests are similar to field tests
(Rossler and Zuna-Kratky 2004, American Bird
Conservancy 2011), but we suggest that the
limitations of tunnel experiments to accurately
simulate windows in actual buildings precludes
this protocol from serving as a definitive tool in
evaluating bird-window collision prevention
methods. We further suggest that the field
experiment protocol described here provides
accurate results to serve as a definitive assessment
of evaluating bird-window collision prevention
methods, because the effectiveness of treatments
are compared in an environment like that of
windows installed in actual buildings. Moreover,
given the limitations of tunnel testing to simulate
windows installed in human structures, we
recommend field experiments with the protocol
we report here be used to verify tunnel testing
results to qualify for Pilot Credit 55 Bird Collision
Deterrence used by the United States Green
Building Council (2011) in their Leadership in
Energy and Environmental Design (LEED) used
to promote the construction of environmentally
friendly structures.
The effectiveness of vertically hung parachute
cords to deter bird collisions is attributable to the
critical spacing between cords, and also as
important is the placement of the cords over the
surface facing the outside. Architects and other
building professionals number the surface of
windows from the outside inward such that
surface number one is that surface facing the
outside environment. Unlike the parachute cords,
glass manufactures that produced the ORNILUX
Mikado using UV signals and other patterns such
as ceramic frit that uses dots, stripes or other
more creative shapes that are also visible to the
human eye are applied to interior surfaces of
multi-pane windows as a means of protecting the
collision deterring pattern from the weathering
effects of the environment. The physical proper-
ties of light absorption, refraction, reflection, and
transmission influence how humans, and almost
certainly birds, perceive patterns applied to
interior window surfaces (Knight 2013). When-
ever interior lighting is equal to or of greater
intensity to that of the outside environment,
patterns applied to surfaces other than surface
one will be visible to birds and humans looking
at the window from the outside. Clear windows
on either side of a corridor (link way) or where
glass walls meet in the corners permit patterns on
interior surfaces of windows to be visible when
viewed from the outside. But when windows
cover darkened interiors such that interior light is
of less intensity than outside, surface one reflects
the facing habitat and sky masking any patterns
on interior window surfaces and rendering them
ineffective in preventing bird strikes. Thus, like
the parachute cords, methods used to prevent
bird-window collisions at windows reflecting the
facing habitat and sky that are applied to surface
one will be most effective. Additional support of
the importance of placing bird-window collision
prevention methods on surface one are results of
previously reported studies in which all external
films applied to surface one, no matter what their
visual appearance, reduced the risk of bird-
window strikes by 59%or more (Klem 2009b).
We thank CPFilms, Solutia, Inc. and T. Port and B.
Lawless-Coale specifically for measuring the UV signal
from ORNILUX Mikado and the parachute cord, and
discovering and reporting the error in UV signal measure-
ment from the external films previously published (Klem
2009b, UV-reflection strength reported as 80%should read
20–40%). We thank C. Mathers and M. K. Erdman for
collecting the individual flight path behavior, and J. D. Flood
and M. Jacob for technical help interpreting the properties of
sheet glass. We are especially grateful to Arnold Glas and
Jeff Acopian for financial support and supplying samples of
ORNILUX Mikado and Acopian BirdSavers for our
experiments, respectively. We thank the anonymous review-
ers and the Editors for extensive suggested modifications that
markedly improved the manuscript. D. Klem, Jr. holds a
patent (US 8,114,503 B2) on the critical spacing between
elements forming a pattern to transform windows into
barriers that birds will avoid. The authors and the Acopian
Center for Ornithology at Muhlenberg College have no
conflict of interest and have not and do not expect to receive
any financial benefit from products described in this study.
AMERICAN BIRD CONSERVANCY. 2011. Tabular summary of
tunnel testing results of bird-window collision deter-
rence. www.usgbc.orgShowFile.aspx?DocumentID
510649 (accessed 11 Jun 2012).
ARNOLD,T.W.AND R. M. ZINK. 2011. Collision mortality
has no discernible effect on population trends of North
American birds. PLoS ONE 6:e24708.
2012. Factors influencing the annual risk of bird-
window collisions at residential structures in Alberta,
Canada. Wildlife Research.
WR11179 (accessed 24 Oct 2012).
BEAN, M. J. 1983. The evolution of national wildlife law.
Praeger, New York, USA.
BENNETT,A.T.D.AND I. C. CUTHILL. 1994. Ultraviolet
vision in birds: what is its function? Vision Research
MAIER. 1996. Ultraviolet vision and mate choice in
Zebra Finches. Nature 380:433–435.
BURKHARDT, D. 1982. Birds, berries and UV. Naturwis-
senschaften 69:153–157.
CORCORAN, L. M. 1999. Migratory Bird Treaty Act: strict
criminal liability for non-hunting caused bird deaths.
Denver University Law Review 77:315–358.
DREWITT,A.L.AND R. H. W. LANGSTON. 2008. Collision effects
of wind-power generators and other obstacles on birds.
Annals New York Academy of Sciences 1134:233–266.
YOUNG,JR., K. J. SERNKA,AND R. E. GOOD. 2001. Avian
collisions with wind turbines: a summary of existing
studies and comparisons to other sources of avian
collision mortality in the United States. National Wind
Coordinating Committee, Washington, D.C., USA.
Scavenging affects persistence of avian carcasses
resulting from window collisions in an urban land-
scape. Journal of Field Ornithology 83:203–211.
AND L. MAYER. 2008. Bird density and mortality at
windows. Wilson Journal of Ornithology 120:550–
1998. Blue Tits are ultraviolet tits. Proceedings of Royal
Society of London, Series B 265:451–455.
KLEM JR., D. 1981. Avian predators hunting birds near
windows. Proceedings of the Pennsylvania Academy
of Science 55:53–55.
KLEM JR., D. 1989. Bird-window collisions. Wilson
Bulletin 101:606–620.
KLEM JR., D. 1990. Collisions between birds and windows:
mortality and prevention. Journal of Field Ornithology
KLEM JR., D. 2006. Glass: a deadly conservation issue for
birds. Bird Observer 34:73–81.
KLEM JR., D. 2009a. Avian mortality at windows: the
second largest human source of bird mortality on
earth. Pages 244–254 in Tundra to tropics: connecting
birds, habitats and people, Proceedings of the Fourth
International Partners in Flight Conference 2008 (T. D.
Rich, C. Arizmendi, D. Demarest and C. Thompson,
Editors). Partners in Flight, McAllen, Texas, USA.
KLEM JR., D. 2009b. Preventing bird-window collisions.
Wilson Journal of Ornithology 121:314–321.
KLEM JR., D. 2010. Sheet glass as a principal human-
associated avian mortality factor. Chapter 20 in Avian
ecology and conservation: a Pennsylvania focus with
national implications (S. K. Majumdar, T. L. Master,
M. Brittingham, R. M. Ross. R. Mulvihill, and J.
Huffman, Editors). Pennsylvania Academy of Science,
Easton, USA.
E. NICIU,AND C. T. PLATT. 2004. Effects of window
angling, feeder placement, and scavengers on avian
mortality at plate glass. Wilson Bulletin 116:69–73.
KNIGHT, R. D. 2013. Physics for scientists and engineers: a
strategic approach, 3rd Edition. Pearson, Glenview,
Illinois USA.
LOSS, S. R., T. WILL,AND P. M. MARA. 2012. Direct human-
caused mortality of birds: improving quantification of
magnitude and assessment of population impact.
Frontiers in Ecology and the Environment 10:357–364.
MARTIN, G. R. 2011 Understanding bird collisions with
man-made objects: a sensory ecology approach. Ibis
ROSSLER,M.AND T. ZUNA-KRATKY. 2004. Vermeidung von
Vogelanprall an Glasflachen. Experimentelle Versuche
zur Wirksamkeit verschiedener Glas-Markierungen bei
Wildvogeln. Bilogische Station Hohenau-Ringelsdorf. (accessed 11 Jun 2012).
SIEGEL, S. 1956. Nonparametric statistics for the behavioral
sciences. McGraw-Hill, New York, USA.
SPSS. 2010. SPSS for Windows, Version 19.0. SPSS,
Chicago, Illinois, USA.
55: bird collision deterrence.
aspx?DocumentID510402 (accessed 11 Jun 2012).
KOIVULA. 1995. Attraction of Kestrels to vole scent
marks in ultraviolet light. Nature 373:425–427.
... Recently, more attention is being paid to finding and using methods that effectively prevent birds from deadly strikes (Klem 2009, Klem & Saenger 2013, Sheppard 2019, Ribeiro & Piratelli 2020. Numerous tests of the surface treatments indicate that opaque vertical stripes of particular widths and separations, as well as some arrangements of opaque dots and other shapes and patterns that do not leave too much open space on the windows (matching "the hand rule"), are effective in reducing bird collisions (Klem 2009, Klem & Saenger 2013, Rössler et al. 2015, Ribeiro & Piratelli 2020. ...
... Recently, more attention is being paid to finding and using methods that effectively prevent birds from deadly strikes (Klem 2009, Klem & Saenger 2013, Sheppard 2019, Ribeiro & Piratelli 2020. Numerous tests of the surface treatments indicate that opaque vertical stripes of particular widths and separations, as well as some arrangements of opaque dots and other shapes and patterns that do not leave too much open space on the windows (matching "the hand rule"), are effective in reducing bird collisions (Klem 2009, Klem & Saenger 2013, Rössler et al. 2015, Ribeiro & Piratelli 2020. However, various types of opaque patterns on glass can be problematic due to the purpose of the building, the architectural vision of the designer, and the preferences of the building users. ...
... Several studies showed that some birds species perceive UV wavelengths from approximately 300-400 nm (Bennett & Cuthill 1994, Hunt et al. 1998, Klem 2009, Swaddle et al. 2020. Klem (2009) described a solution that uses ultraviolet (UV) signals in the form of adjacent and contrasting UV-reflecting and UV-absorbing elements, while Klem & Saenger (2013) found external films with UV-reflecting components of 20-40% over 300-400 nm to effectively prevent bird-window collisions. Importantly and unlike some experimental studies performed in a flight tunnel, we confirmed the effectiveness of the UV Typically of field studies, we were not able to fully control conditions and there may have been more bird strikes on the glass panels of both control and film-covered shelters than recorded by us. ...
Full-text available
It is estimated that millions of birds globally die due to collisions with glass surfaces. In order to reduce this mortality, it is essential to provide an objective assessment of the effectiveness of bird-friendly preventive methods. Several types of opaque films and stickers are available nowadays and can be highly effective in protecting birds from fatal collisions. However, by being visible to the human eye, they can affect the users' quality of view from within protected spaces. Products that take advantage of the birds' ability to see ultraviolet light seem to offset these impediments. This study determines if UV-reflective BirdShades film prevents birds from collisions with glass in natural environmental conditions. We monitored eight glass bus stops, where we had previously recorded high numbers of birds collisions. On four of them, we applied UV film, and the other four bus stops were used as control. A generalized additive mixed model showed a significant interaction between time (before vs. after) and film UV treatment (control vs. treated). Before the treatment, the number of collisions tended to be higher at treated bus shelters than control. However, this significantly changed after the treatment, suggesting that UV film reduces bird glass collision rate over 5-fold. Our study is the first worldwide that tested UV film on glass shelters and supports a conclusion that the UV film efficiently reduces the risk of bird collision.
... For example, when there is more glass surface area on window facades, there are more collisions (Borden et al. 2010, Cusa et al. 2015, Kummer et al. 2016, Brown et al. 2020. When reflection is maximized by replacement of a window with a mirror or the application of a highly reflective coating, researchers have observed more collisions (Klem and Saenger 2013, Cusa et al. 2015, Brown et al. 2020. ...
... The finches used in the study were raised in captivity and were somewhat accustomed to human presence and handling. Using a captive-reared species might minimize some effects of human-induced stress on bird behavior during flight trials (Klem and Saenger 2013). We also know that Zebra Finches respond similarly to a wild-caught species (Brown-headed Cowbird, Molothrus ater) in flight trials (Swaddle et al. 2020). ...
... For example, industry-standard flight tunnel studies have generally lacked natural daylight (Sheppard 2019), excluded direct sunlight (Rössler et al. 2015), and/or reduced reflective surfaces (Rössler et al. 2015, Sheppard 2019. In-field tests of window-collision mitigation strategies have included natural daylight but have not incorporated the interior backlighting that is common in buildings (Klem 1990, Klem et al. 2004, Klem 2009, Klem and Saenger 2013. Taken together with our results indicating that lighting conditions have an unpredicted influence on risk of collisions, we call for adaptation of standard protocols to incorporate more realistic lighting conditions when assessing products that might reduce the risk of bird-window collisions. ...
Full-text available
Bird-window collisions account for approximately one billion bird deaths annually in North America. Highly reflective or mirrored glass is associated with increased collision risk, but little is known about whether the reflection caused by differential lighting of otherwise clear glass influences the risk of window collisions. We aimed to determine whether reflection from a clear window influences daytime collision risk by manipulating the lighting conditions on exterior and interior window surfaces. In a flight tunnel, we flew domesticated Zebra Finches (Taeniopygia guttata) toward windows manipulated to be of higher or lower reflection and recorded collision risk and flight velocity using three-dimensional videography. We predicted that risk of collision would be greater when windows were manipulated to be more reflective. We found no support for this prediction. In contrast, we found that collision risk decreased in the presence of a stronger reflection during bright, midday exterior lighting conditions. We suggest that the influence of window reflection on daytime window collisions is more complex than often assumed and might involve previously unaccounted properties of light, such as the polarity of light. Lastly, we recommend directions for future collision research and non-invasive mitigation strategies which involve the manipulation of interior lighting throughout the day.
... In addition to logistical limitations, the potential benefits or effects of the ACAS on other fauna are unknown. Several studies document collisions of birds and bats with structures such as power lines, guy wires, communication towers, meteorological towers (Markus 1972, Banks 1979, Haas 1980, Ferrer and Hiraldo 1991, Janss 2000, Shire et al. 2000, Erickson et al. 2005, Wright et al. 2009, Gehring et al. 2011, Kerlinger et al. 2012, Longcore et al. 2012, Klem and Saenger 2013, Bernardino et al. 2018, Dwyer et al. 2019, and wind turbines (Hein and Schirmacher 2016, Katzner et al. 2016, Smith and Dwyer 2016. It is possible that other collision-prone species could benefit from ACAS illumination of dangerous structures. ...
Collisions with anthropogenic structures by long-distance migrants and threatened and endangered species are a growing global conservation concern. Increasing the visibility of these structures may reduce collisions but may only be accepted by local residents if it does not create a visual disturbance. Recent research has shown the potential for ultraviolet (UV) light, which is nearly imperceptible to humans, to mitigate avian collisions with anthropogenic structures. We tested the effectiveness of two UV (390–400 nm) Avian Collision Avoidance Systems (ACASs) at reducing collisions at two 260-m spans of marked power lines at the Iain Nicolson Audubon Center at Rowe Sanctuary, an important migratory bird stopover location in Nebraska. We used a randomized design and a tiered model selection approach employing generalized linear models and the Akaike Information Criterion to assess the effectiveness of ACASs considering environmental (e.g., precipitation) and detection probability (e.g., migration chronology) variables. We found focal (assessed power line) and distal (neighboring power line) ACAS status and environmental variables were important predictors of avian collisions. Our top model suggests that the focal ACAS illumination reduced collisions by 88%, collisions were more likely at moderate (10–16 km/h) compared to lower or higher wind speeds, and collision frequency decreased with precipitation occurrence. Our top model also indicates that the distal ACAS illumination reduced collisions by 39.4% at the focal power line when that ACAS was off, suggesting a positive “neighbor effect” of power line illumination. Although future applications of ACASs would benefit from additional study to check for potential negative effects (for example, collisions involving nocturnal foragers such as bats or caprimulgiform birds drawn to insects), we suggest that illuminating power lines, guy wires, towers, wind turbines, and other anthropogenic structures with UV illumination will likely lower collision risks for birds while increasing human acceptance of mitigation measures in urban areas.
... Window decals have successfully reduced average monthly bird-window collisions by 84% (Ocampo-Peñuela et al., 2016). Application of collision prevention decals to the exterior surface of windows (Klem & Saenger, 2012), or tinting of windows (Erickson et al., 2005), are viable solutions to prevent bird-building collisions and citizen science can assist with community-level implementations. ...
Full-text available
Data from wildlife rehabilitation centers (WRCs) can provide on-the-ground records of causes of raptor morbidity and mortality, allowing threat patterns to be explored throughout time and space. We provide an overview of native raptor admissions to four WRCs in England and Wales, quantifying the main causes of morbidity and mortality , trends over time, and associations between threats and urbanization between 2001 and 2019. Throughout the study period, 14 raptor species were admitted totalling 3305 admission records. The Common Buzzard (Buteo buteo; 31%) and Tawny Owl (Strix aluco; 29%) were most numerous. Relative to the proportion of breeding individuals in Britain and Ireland, Peregrine Falcons (Falco peregrinus), Little Owls (Athene noctua), and Western Barn Owls (Tyto alba) were over-represented in the admissions data by 103%, 73%, and 69%, respectively. Contrastingly Northern Long-eared Owls (Asio otus), Western Marsh Harriers (Circus aeruginosus), and Merlin (Falco columbarius) were under-represented by 187%, 163%, and 126%, respectively. Across all species, vehicle collisions were the most frequent anthropogenic admission cause (22%), and orphaned young birds (10%) were most frequent natural cause. Mortality rate was highest for infection/parasite admissions (90%), whereas orphaned birds experienced lowest mortality rates (16%). For one WRC, there was a decline in admissions over the study period. Red Kite (Milvus milvus) admissions increased over time, whereas Common Buzzard and Common Kestrel admissions declined. There were significant declines in the relative proportion of persecution and metabolic admissions and an increase in orphaned birds. Urban areas were positively associated with persecution, building collisions, and unknown trauma admissions, whereas vehicle collisions were associated with more rural areas. Many threats persist for raptors in England and Wales, however, have not changed substantially over the past two decades. Threats associated with urban areas, such as building collisions, may increase over time in line with human population growth and subsequent urban expansion.
... Many of these efforts have focused on making structures more visible to birds [e.g. 17,18]. Some methods have been successful, such as applying various types of markings on glass windows [19], altering the coloration of wind turbine blades [20], marking ground wires on transmission power lines [21], and adding dynamic lighting atop towers at night and in overcast conditions [22,23]. ...
Full-text available
Billions of birds fatally collide with human-made structures each year. These mortalities have consequences for population viability and conservation of endangered species. This source of human-wildlife conflict also places constraints on various industries. Furthermore, with continued increases in urbanization, the incidence of collisions continues to increase. Efforts to reduce collisions have largely focused on making structures more visible to birds through visual stimuli but have shown limited success. We investigated the efficacy of a multimodal combination of acoustic signals with visual cues to reduce avian collisions with tall structures in open airspace. Previous work has demonstrated that a combination of acoustic and visual cues can decrease collision risk of birds in captive flight trials. Extending to field tests, we predicted that novel acoustic signals would combine with the visual cues of tall communication towers to reduce collision risk for birds. We broadcast two audible frequency ranges (4 to 6 and 6 to 8 kHz) in front of tall communication towers at locations in the Atlantic migratory flyway of Virginia during annual migration and observed birds' flight trajectories around the towers. We recorded an overall 12-16% lower rate of general bird activity surrounding towers during sound treatment conditions, compared with control (no broadcast sound) conditions. Furthermore, in 145 tracked "at-risk" flights, birds reduced flight velocity and deflected flight trajectories to a greater extent when exposed to the acoustic stimuli near the towers. In particular, the 4 to 6 kHz stimulus produced the greater effect sizes, with birds altering flight direction earlier in their trajectories and at larger distances from the towers, perhaps indicating that frequency range is more clearly audible to flying birds. This "acoustic lighthouse" concept reduces the risk of collision for birds in the field and could be applied to reduce collision risk associated with many human-made structures, such as wind turbines and tall buildings.
Full-text available
Background In North America, up to one billion birds are estimated to die annually due to collisions with glass. The transparent and reflective properties of glass present the illusion of a clear flight passage or continuous habitat. Approaches to reducing collision risk involve installing visual cues on glass that enable birds to perceive glass as a solid hazard at a sufficient distance to avoid it. Methods We monitored for bird-window collisions between 2013 and 2018 to measure response to bird protection window treatments at two low-rise buildings at the Alaksen National Wildlife Area in Delta, British Columbia, Canada. After 2 years of collision monitoring in an untreated state, we retrofitted one building with Feather Friendly® circular adhesive markers applied in a grid pattern across all windows, enabling a field-based assessment of the relative reduction in collisions in the 2 years of monitoring following treatment. An adjacent building that had been constructed with a bird protective UV-treated glass called ORNILUX® Mikado, was monitored throughout the two study periods. Carcass persistence trials were conducted to evaluate the likelihood that carcasses were missed due to carcass removal between scheduled searches. Results and Conclusions After accounting for differences in area of glass between the two buildings, year, and observer effects, our best-fit model for explaining collision risk included the building’s treatment group, when compared to models that included building and season only. We found that the Feather Friendly® markers reduced collision risk at the retrofitted building by 95%. Collision incidence was also lower at the two monitored façades of the building with ORNILUX® glass compared to the building with untreated glass. Although more research is needed on the effectiveness of bird-protection products across a range of conditions, our results highlight the benefit of these products for reducing avian mortality due to collisions with glass.
Many interactions between humans and animals take place in the urban environment; a fascinating domain, investigation into which reveals a dense web of cause and effect. As urban zones develop and sprawl into rural areas, animals have been adapting to, thriving in and even evolving due to urban spaces that meet their fundamental needs. However, research has proven that many anthropogenic activities directly and indirectly threaten urban wildlife welfare, many of which occur on levels far exceeding the mortality rates of many other interactions with animals. While this piece argues, indeed, for the protection of animal welfare as a value worth protecting in itself, it provides compelling evidence that effectively managing the relationship between humans and urban wildlife is in the interests of both humans and animals. This is based on unequivocal evidence that a failure to effectively manage interactions between human and urban wildlife populations presents potentially severe threats to human health and welfare also. As management is key for minimising conflict, the key measures that are taken to this end will be set out. These include studying and surveying animal populations; developing policies and guidelines that limit ineffective management practices; developing green infrastructure; and generating public awareness and fostering individual responsibility. In light of the argument and reasoning presented, this piece will conclude with a critical assessment of the extent to which the term brethren could currently be applied to the relationship between humans and animals in the urban environment.KeywordsUrban wildlifePublic awarenessCoexistenceAnthropogenic activitiesMutual interestAnimal sentience
Animal behavior plays a critical role in conservation efforts. Efforts to captively breed endangered species hinge on understanding the species’ habitat requirements, mating behavior, and parent–offspring interactions. Conservation of species in the wild by creating sanctuaries is most successful if aspects of behavior such as territoriality, dispersal, and migration are factored into sanctuary design. Animal behavior gives biologists tools for measuring the level of disturbance that humans create for wild populations. Encroachment of humans into wildlife habitats makes human–wildlife interactions more frequent and behavior gives us clues about how to minimize negative impacts of humans on wildlife as well as how to help humans avoid injury when they encounter wildlife. Some species of wildlife have become more adept at living in towns and cities, bringing with them damage to landscaping, risk of disease spread, and in some cases risk of injury to humans or their companion animals. Animal behavior helps us to understand how to minimize these impacts and how to improve human–animal co-existence in urban and suburban settings. As human populations continue to expand and climate change impacts on wildlife intensify, knowledge of animal behavior will become increasingly important in conservation efforts.
Due to the continuous rising ambient levels of nonionizing electromagnetic fields (EMFs) used in modern societies-primarily from wireless technologies-that have now become a ubiquitous biologically active environmental pollutant, a new vision on how to regulate such exposures for non-human species at the ecosystem level is needed. Government standards adopted for human exposures are examined for applicability to wildlife. Existing environmental laws, such as the National Environmental Policy Act and the Migratory Bird Treaty Act in the U.S. and others used in Canada and throughout Europe, should be strengthened and enforced. New laws should be written to accommodate the ever-increasing EMF exposures. Radiofrequency radiation exposure standards that have been adopted by worldwide agencies and governments warrant more stringent controls given the new and unusual signaling characteristics used in 5G technology. No such standards take wildlife into consideration. Many species of flora and fauna, because of distinctive physiologies, have been found sensitive to exogenous EMF in ways that surpass human reactivity. Such exposures may now be capable of affecting endogenous bioelectric states in some species. Numerous studies across all frequencies and taxa indicate that low-level EMF exposures have numerous adverse effects, including on orientation, migration, food finding, reproduction, mating, nest and den building, territorial maintenance, defense, vitality, longevity, and survivorship. Cyto- and geno-toxic effects have long been observed. It is time to recognize ambient EMF as a novel form of pollution and develop rules at regulatory agencies that designate air as 'habitat' so EMF can be regulated like other pollutants. Wildlife loss is often unseen and undocumented until tipping points are reached. A robust dialog regarding technology's high-impact role in the nascent field of electroecology needs to commence. Long-term chronic low-level EMF exposure standards should be set accordingly for wildlife, including, but not limited to, the redesign of wireless devices, as well as infrastructure, in order to reduce the rising ambient levels (explored in Part 1). Possible environmental approaches are discussed. This is Part 3 of a three-part series.
Full-text available
Background Research on bird-window collision mitigation is needed to prevent up to a billion bird fatalities yearly in the U.S. At the University of Utah campus (Salt Lake City, Utah, USA), past research documented collisions, especially for Cedar Waxwings ( Bombycilla cedrorum ) drawn to fruiting ornamental pears in winter. Mirrored windows, which have a metallic coating that turns window exteriors into mirrors, had frequent collisions, which were mitigated when Feather Friendly®bird deterrent markers were applied. Bird-friendly windows–ORNILUX®ultraviolet (UV) and fritted windows–also reduced collisions when data were collected across fall and winter. Extending this prior research, we evaluated additional mitigation and tested the replicability of effects for pear trees, mirrored windows, and bird-friendly windows across two years. Methods Using published data from eight buildings monitored for collisions in year 1 (Fall and Winter, 2019–2020), we added another year of monitoring, Fall and Winter, 2020–2021. Between years, Feather Friendly®mitigation markers were added to collision-prone areas of two buildings, including both mirrored and transparent windows. Results The two buildings that received new Feather Friendly®mitigation had significantly fewer collisions post-mitigation. Control areas also had nonsignificant decline in collisions. The interaction of area (mitigation vs. control) by time (year 1 vs. 2) was significant, based on generalized estimating equations (GEE). The total yearly collisions across all eight buildings declined from 39 to 23. A second GEE analysis of all 8 buildings showed that mirrored windows, pear trees, and bird-friendly windows were each significant when analyzed separately. The best-fit model showed more collisions for mirrored windows and fewer collisions for bird-friendly windows. We found pear tree proximity to be related to more collisions in winter than fall. In addition, pear trees showed reduced collisions from year 1 to 2, consistent with new mitigation for two of three buildings near pear trees. Discussion Feather Friendly ® markers can mitigate collisions with transparent windows, not only mirrored windows, compared to unmitigated areas over 2 years. Results also underscore the dangers of pear tree proximity and mirrored windows and the efficacy of bird-friendly windows. Thus, bird collisions can be prevented by window mitigation, permanent bird-friendly windows, and landscape designs that avoid creating ecological traps.
Full-text available
Collisions of birds with windows were studied by reviewing the literature, collecting data from museums and individuals, monitoring man-made structures, and conducting field experiments. Approximately 25% (225/917) of the avian species in the United States and Canada have been documented striking windows. Sex, age, or residency status have little influence on vulnerability to collision. There is no season, time of day, and almost no weather condition during which birds elude the window hazard. Collisions occur at windows of various sizes, heights, and orientations in urban, suburban, and rural environments. Analyses of experimental results and observations under a multitude of conditions suggest that birds hit windows because they fail to recognize clear or reflective glass panes as barriers. Avian, manmade structural, or environmental features that increase the density of birds near windows can account for strike rates at specific locations. A combination of interacting factors must be considered to explain strike frequency at any particular impact site. The earliest account of a bird hitting a window in North America is by Nuttall (1832:88). He described a Sharp-shinned Hawk (Accipiter striatus) which, in the pursuit of prey, flew through two panes of greenhouse glass only to be stopped by a third. Townsend (1931) described a series of five fatalities of the Yellow-billed Cuckoo (Coccyzus americanus). His paper was the first to suggest that avian vulnerability to windows may be more marked in some species than in others and that specific windows claim a succession of victims. He termed the victims "tragedies" and apparently regarded them as rare, self-destroying incompetents. Picture windows were relatively uncommon through the end of World War II, and there was little reason for concern about their threat to birds. In the postwar period, a building boom stimulated the rapid expansion of the sheet glass industry, and large glass windows were incorporated into the designs of new and remodeled structures. Today, it is not uncommon to find modern buildings that are entirely surfaced with glass. I found 88 papers reporting bird-window collisions, primarily after the mid-1940s (Klein 1979). They document strikes in North America, South America, West Indies, Europe, and Africa, and, with few exceptions are cited in annotated bibliographies on man-caused mortality to birds (Weir 1976, Avery et al. 1980). However, most textbooks and encyclopedia treatments of ornithology present little, if any, description of the fatal hazards that windows pose to birds. The sheet glass industry and its commercial allies appear to be unaware of the problem. On the other hand, I found avian fatalities resulting from window strikes to be common knowledge among the general public. Birds have been reported to strike two general types of windows as classified according to their visual effects on the human eye. These are transparent windows which appear invisible and reflective windows which mirror the facing outside habitat. Two general types of collisions have been described (Wallace and Mahan 1975:456) and both reveal the ability of glass to misinform and misguide at least some birds. One primarily involves birds such as Northern Cardinal (Cardinalis cardinalis) that commonly flutter against picture windows and harmlessly peck the glass during the spring and summer. These birds seldom, if ever, stun or injure themselves or shatter the glass and usually are males defending their territories against their reflected images. In the second type, birds fly into transparent or reflective windows as if unaware of their presence. These collisions often have fatal consequences, and are the subject of this paper. In this paper my objectives are: (1) to propose an explanation for why birds collide with windows, (2) to describe and analyze species, environmental and manmade structural characteristics associated with bird-window collisions in the United States and Canada, and (3) to suggest how these select characteristics account for the differential frequency with which birds strike windows in various man-made structures.
Full-text available
Records of avian predators hunting in the vicinity of windows were obtained from 1974 to 1979. These data indicate that Ac- cipiter hawks and Loggerhead Shrikes (Lanius ludovicionus) are capable of exploiting prey-catching opportunities in human- modified environments by learning that prey are easily available near windows. The data further show that these predators kill themselves by flnng into nearby windows while hunting. At least for accipiters and especially the Sharp-shinned Hawk (,4. striatus), the habit of hunting birds at feeding stations near win- dows may explain why these raptors become frequent window- kills.
Context. Increasingly, ornithologists are being asked to identify major sources of avian mortality so as to identify conservation priorities. Aims. Considerable evidence suggests that windows of office towers are a lethal hazard for migrating birds. The factors influencing the risk of bird-window collisions in residential settings are not understood as well. Methods. Citizen scientists were requested to participate in an online survey that asked about characteristics concerning their homes and yards, general demographic information about participants, and whether they had observed evidence of bird-window collisions at their home. Key results. We found that 39.0% of 1458 participants observed a bird-window collision in the previous year. The mean number of reported collisions was 1.7 +/- 4.6 per residence per year, with 38% of collisions resulting in a mortality. Conclusions. Collisions were not random, with the highest collision and mortality rates at rural residences, with bird feeders > rural residences without feeders > urban residences with feeders > urban residences without feeders > apartments. At urban houses, the age of neighbourhood was a significant predictor of collision rates, with newer neighbourhoods reporting fewer collisions than older neighbourhoods. Most people remembered collisions occurring in the summer months. Implications. Our results are consistent with past research, suggesting that window collisions with residential homes are an important source of mortality for birds. However, we found large variation in the frequency of collisions at different types of residences. Proper stratification of residence type is crucial to getting accurate estimates of bird-window collisions when scaling local data into larger-scale mortality estimates.
It has been estimated that from 100 million to well over 1 billion birds are killed annually in the United States due to collisions with human-made structures, including vehicles, buildings and windows, powerlines, communication towers, and wind turbines. Although wind energy is generally considered environmentally friendly (because it generates electricity without emitting air pollutants or greenhouse gases), the potential for avian fatalities has delayed and even significantly contributed to blocking the development of some windplants in the U.S. Given the importance of developing a viable renewable source of energy, the objective of this paper is to put the issue of avian mortality associated with windpower into perspective with other sources of avian collision mortality across the U.S. The purpose of this paper is to provide a detailed summary of the mortality data collected at windplants and put avian collision mortality associated with windpower development into perspective with other significant sources of avian collision mortality across the United States. We provide a summary of data collected at many of the U.S. windplants and provide annual bird fatality estimates and projections for all wind turbines in the U.S. For comparison, we also review studies of avian collision mortality from other major human-made structures and report annual bird fatality estimates for these sources. Other sources also significantly contribute to overall avian mortality. For example, the National Audubon Society estimates avian mortality due to house cats at 100 million birds per year. Pesticide use, oil spills, disease, etc., are other significant sources of unintended avian mortality. Due to funding constraints, the scope of this paper is limited to examining only avian mortality resulting from collisions with human-made obstacles.
Bird strikes were recorded at the windows of commercial and private buildings to study the effects of collision mortality on birds, and several experiments were conducted to evaluate methods of preventing collisions between birds and glass panes. Two single houses that were systematically monitored annually killed 33 and 26 birds, respectively. Collisions at one house in the same 4-mo period (September- December) in consecutive years resulted in 26 and 15 fatalities, respectively. At least one out of every two birds were killed striking the windows of these single dwellings. The records from these homes also revealed that window strikes are equally lethal for small and large species. The annual mortality resulting from window collisions in the United States is estimated at 97.6-975.6 million birds. Experimental evidence indicates that complete or partial covering of windows will eliminate bird strikes. If parts of the window are altered, objects or patterns placed on or near the window must be no more than 5-10 cm apart and uniformly cover the entire glass surface. Eliminating bird attractants from the vicinity of windows will reduce or prevent strikes by reducing the number of birds near the glass hazard. If removal of attractants is unacceptable, place them within 0.3 m of the glass surface; birds are drawn to the attractant on arrival and are not able to build up enough momentum to sustain serious injury if they hit upon departure. My experimental results further reveal that the common practice of placing single objects such as falcon silhouettes or owl decoys on or near windows does not significantly reduce bird strikes. Window casualties represent a potentially valuable, but largely neglected source of data capable of contributing information on species geographic distributions, migration patterns, and various other studies requiring specimens.