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Many methods to prevent bird deaths at windows are ineffective, and some useful methods are expensive or displeasing. Here we offer, for free download, an image that ended bird accidents on large windows near a tropical cloud forest area, and propose hypotheses for its experimental evaluation
UNED Research Journal (ISSN: 1659-441X) Vol. 10(1): 83-84, June, 2018
A new, cheap method to reduce bird mortality from window collisions
Julián Monge-Nájera & Zaidett Barrientos Llosa
Laboratorio de Ecología Urbana, Universidad Estatal a Distancia (UNED), 2050 San José, Costa Rica,
ABSTRACT: Many methods to prevent bird deaths at windows are in-
eective, and some useful methods are expensive or displeasing. Here
we oer, for free download, an image that reduced bird accidents on
large windows near a tropical cloud forest area, and propose hypothe-
ses for its experimental evaluation.
Key words: reduction of bird mortality, predator-avoidance behavior,
reaction of birds to cats.
RESUMEN: Un método barato para reducir la mortalidad de aves
por choque con ventanas. Muchos métodos para evitar la muerte
de aves en ventanas son inecientes, y algunos métodos ecaces re-
sultan caros o desagradables. Aquí ofrecemos, para descarga gratui-
ta, una imagen que redujo las muertes de aves en la cercanía de un
bosque tropical nuboso. Además, proponemos hipótesis para su
evaluación experimental.
Palabras clave: reducción de mortalidad, evasión de depredadores,
reacción de aves ante gatos.
Bird injury and death from collisions with win-
dow glass is a signicant problem around the world
(Menacho-Odio, 2015; Hager et al., 2017). Unfortunately,
even though public participation and awareness are
growing (Oviedo & Menacho-Odio, 2015; Kummer, Bayne
& Machtans, 2016), methodological problems limit our
understanding of the problem and its remediation (Loss,
Loss, Will & Marra, 2016).
Some methods to prevent bird deaths at windows
are ineective, and some eective methods are expen-
sive or displeasing (for a methods review, see Cowell,
Dietrich, Sullivan & Messmer, 2017). Here we present
several hypotheses based on observations with a printed
photograph that helped reduce bird mortality on large
windows near a tropical cloud forest area. We include the
photograph (free download)
The building where the test was done is surround-
ed by cattle grassland and is 70 m from tropical ripari-
an cloud forest in Coronado, Costa Rica (10°00’42’’N,
83°57’58’’W). No detailed records were kept because it
was impossible to keep observers in the house all the
time, but our experience is that bird collisions were rare
in the rst ve years. More than half the victims died on
impact, others died after a few minutes, and a few recov-
ered and ew away.
Received 20-X-2017 • Corrected 14-XI-2017 • Accepted 12-XII-2017
After the fth year, secondary vegetation grew closer
to the building and birds started to die every week and
then every day, leading us to look for a solution. After
noticing that no birds hit when our cats were closed to
the windows, we decided to test a photograph of one of
them, a novel idea that to our knowledge has not been
published before.
On May 17th, 2017, we pasted to the base of one win-
dow a 30cm tall color photograph of our cat Negrito (Fig.
1) and no more deaths took place in that window, so on
August 5th, 2017 we added the photograph to the re-
maining seven windows. Since then (almost a year at the
date of this publication) we have only witnessed one bird
death in windows with the cat image (and ve collisions
in which the birds survived).
The idea of using a predator image to save birds is
not new: hawk silhouettes have been used for years, but
they were not successful; basically, only threads, nets or
materials that cover a signicant part of the window had
worked until now (see Klem, 1990, Menacho-Odio, 2018).
We think that previous predator images failed because
they were not realistic enough to scare birds, leaving
only the option of covering much of the glass, which
is often not a desirable practice from the point of view
of the human occupants of buildings, who build large
84 UNED Research Journal (ISSN: 1659-441X) Vol. 10(1): 83-84, June, 2018
windows to get an unobstructed view of the scenery. In
our experience, this image of a cat, visible from a long
distance thanks to its contrasting colors, shape and size,
prevented further deaths. We hope others will use it and
report on its ecacy, hopefully pasting it in in the out-
side of some windows (to prevent reections) and leav-
ing other windows as experimental controls, to see the
before-and-after dierence in the number of birds dying.
A similar image, but with random areas of black and yel-
low, can be used as part of the control to see if it is real-
ly the cat image that produces the avoidance eect in
birds. If our results are conrmed, tests should be made
to measure the area that each image provides, as well as
the best position of the photograph in the window.
Our hypotheses are that the image of a predator pre-
vents more accidents that the image of an herbivore;
that color images work better than gray images or silhou-
ettes; and that images in which you see the eyes clearly
or show the open mouth of a predator avoid more col-
lisions. Of course, many other hypotheses can be imag-
ined by future researchers.
We thank an anonymous reviewer for suggestions to
improve the manuscript.
Cowell, S., Dietrich, C., Sullivan, K., & Messmer, T. (2017).
Reducing the Risk of Birds Colliding into Windows: A
Practical Guide for Homes and Businesses. Utah State
University Extension Paper, 1661. Retrieved from http://
Hager, S. B., Cosentino, B. J., Aguilar-Gómez, M. A., Anderson,
M. L., Bakermans, M., Boves, T. J., ... & Calderón-Parra,
R. (2017). Continent-wide analysis of how urbaniza-
tion aects bird-window collision mortality in North
America. Biological Conservation, 212, 209-215. doi:
Klem, D., Jr. (1990). Collisions between birds and windows:
Mortality and prevention. Journal of Field Ornithology,
61(1), 120-128.
Kummer, J. A., Bayne, E. M., & Machtans, C. S. (2016). Use of ci-
tizen science to identify factors aecting bird–window
collision risk at houses. The Condor, 118(3), 624-639. doi:
Loss, S., Loss, S., Will, T., & Marra, P. (2016). Best practices for data
collection in studies of bird-window collisions. Retrieved
Menacho-Odio, R. M. (2015). Colisión de aves contra ventanas
en Costa Rica: conociendo el problema a partir de datos
de museos, ciencia ciudadana y el aporte de biólogos.
Zeledonia, 19, 10-17.
Menacho-Odio, R. M. (2018). Local perceptions, attitudes, be-
liefs, and practices toward bird-window collisions in
Monteverde, Costa Rica. UNED Research Journal, 10(1),
Oviedo, S., & Menacho-Odio, R. M. (2015). Actitud en la prefe-
rencia de métodos para evitar el choque de aves contra
puertas y ventanas de vidrio en Costa Rica. Zeledonia,
19, 22-31.
Fig. 1. Cat photograph that prevented deaths from bird colli-
sions when placed on windows near a tropical cloud forest.
See Digital Appendix at: / Ver Apéndice digital en:
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
ABSTRACT: Bird-window collisions are an important cause of bird mortality worldwide. Reducing collisions requires understanding of the costs and benefits perceived by stakeholders. I consulted two focus groups, conducted 18-semi-structured interviews and applied surveys to 58 residents of Monteverde, Costa Rica, to understand their perception of the problem. Many reported collisions in their houses but there is a lack of information about the magnitude of the situation. Black silhouettes are the most frequent method of prevention, even though they are mostly ineffective. The main factors for selecting methods include unblocked views, aesthetics, effectiveness, ease of installation and removal, and ease of maintenance. The preferred effective method was cords (Acopian Bird Savers), and painted dots was the least liked. I recommend education about effective methods for Monteverde and similar communities.
Full-text available
Bird-window collisions at houses have been identified as a significant source of mortality for North American birds, but which types of houses and windows are most problematic remains poorly understood. We assessed how neighborhood type, yard conditions, house attributes, and window type influenced collision rates. Data were collected from citizen scientists across Alberta, Canada, who surveyed their houses daily. In relation to the best-fitting model, the yard model explained 58.1% of the explained deviance, the neighborhood model 45.6%, and the house model 42.6%. The factors that had the largest effect for predicting collision risk included season and whether the house was in a rural or an urban area (rural areas in the fall had a 6.0× higher collision risk than urban areas in the winter), the height of vegetation in the front yard of the house (trees >2 stories high increased collision risk by 3.6× compared to houses with no trees), and the presence of a bird feeder (which increased collision risk by 1.7×). This suggests that multiple factors affect collision rates and that the suitability of a yard as bird habitat is likely a key driver. Given that few homeowners are likely to take an approach that reduces the number of birds in their yards, future focus needs to be given to bird-friendly urban design and developing the most effective window deterrents so that collisions can be reduced and birds enjoyed in urban environments.
Full-text available
The objective of the study was to analyze the preference of Costa Ricans in relation to methods to avoid the collision of birds against the glass doors and windows. During the investigation we used methods that included observations, and implementation of interviews and surveys. The interviews and surveys were carried out during the months of March and April 2014 in six of the seven provinces of Costa Rica. As a result, the participation of 77 people was obtained, some methods implemented were selected because they were recomended by other people, because of the versatility of the methods or monetary investment they represent. Moreover, the choice of methods was related to the aesthetics of the window, as it is important for participants to maintain this aesthetics because of the economic cost of design, construction, comfort, light and landscape view. there were others who did not consider aesthetic as important, to the point of hanging dry bromeliads, thin bamboo poles implement, among other methods.
Full-text available
This study consisted of recording of bird species which have collided on glass windows or doors in Costa Rica. The data were obtained from a review of Specimens of the National Museum of Costa Rica and the Museum of Zoology at the University of Costa Rica also data collections made by biologists and information submitted by scientists citizens of the social networking group of the Ornithological Association of Costa Rica. As a result a list of 131 species of birds that have presented collisions with windows was compiled Costa Rica. Among these are birds with small populations like the bell bird Procnias tricarunculatus (n = 4) and the parrot Pyrilia haematoti. We also found that Individuals of species with declining populations such as the Black face solitaire Myadestes melanops and the Resplendent Quetzal (n = 1) have presented collisions with windows. Among the 74 found resident species, species typical of tropical forests were found, as jacamar, toucans, woodpeckers and woodcreepers. Some of the families with the highest number of species collisions is presented hummingbirds (Trochilidae), thrushes (Turdidae) and manakins (Pipridae). Moreover, 24 migratory species and eight resident species he encountered some degree endemism. The results are preliminary, as the way to get the data implies a bias because some parts of Costa Rica as Monteverde, La Selva de Sarapiqui Station and San Vito de Coto Brus, are favored by the presence of biologists and naturalists in areas that facilitate as much information than other areas of the country.
Full-text available
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.
Characteristics of buildings and land cover surrounding buildings influence the number of bird-window collisions, yet little is known about whether bird-window collisions are associated with urbanization at large spatial scales. We initiated a continent-wide study in North America to assess how bird-window collision mortality is influenced by building characteristics, landscaping around buildings, and regional urbanization. In autumn 2014, researchers at 40 sites (N = 281 buildings) used standardized protocols to document collision mortality of birds, evaluate building characteristics, and measure local land cover and regional urbanization. Overall, 324 bird carcasses were observed (range = 0–34 per site) representing 71 species. Consistent with previous studies, we found that building size had a strong positive effect on bird-window collision mortality, but the strength of the effect on mortality depended on regional urbanization. The positive relationship between collision mortality and building size was greatest at large buildings in regions of low urbanization, locally extensive lawns, and low-density structures. Collision mortality was consistently low for small buildings, regardless of large-scale urbanization. The mechanisms shaping broad-scale variation in collision mortality during seasonal migration may be related to habitat selection at a hierarchy of scales and behavioral divergence between urban and rural bird populations. These results suggest that collision prevention measures should be prioritized at large buildings in regions of low urbanization throughout North America.
Reducing the Risk of Birds Colliding into Windows: A Practical Guide for Homes and Businesses
  • S Cowell
  • C Dietrich
  • K Sullivan
  • T Messmer
Cowell, S., Dietrich, C., Sullivan, K., & Messmer, T. (2017). Reducing the Risk of Birds Colliding into Windows: A Practical Guide for Homes and Businesses. Utah State University Extension Paper, 1661. Retrieved from http://