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Classic Towerkill Documents & Recent Literature
(chronologically listed)
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Cochran, William W. and Richard R. Graber. 1958. Attraction of nocturnal migrants by lights on a television tower. Wilson Bulletin, 70:378-380.

Cochran and Graber made visual and acoustic observations of birds circling a 984-ft TV tower near Champaign, Illinois during a night with overcast and light mist. They counted call notes from migrants and made observations of the number of birds flying in the vicinity of the tower with a spotlight. Cochran was the engineer at the TV station and was able to control the lighting of the tower. By turning off the lights for short periods of time, he and Graber were able to confirm what many had suspected - that lights were causing the birds to concentrate around the tower. Within a few minutes of turning off the tower lights, the swarm of birds hanging around the tower dispersed.

A copy of this paper may be obtained online from the Searchable Ornithological Research Archive http://elibrary.unm.edu/sora/



Graber, R. R. 1968. Nocturnal migration in Illinois - Different points of view. Wilson Bulletin, 80, 36-71.

In his classic study of night migration in Illinois, Graber compared simultaneous, acoustic, radar, and towerkill data, along with concurrent field censuses. In his report he speculates on the mechanism of towerkills as follows:

"Migrants approaching the tower enter a lighted area from which they are reluctant to leave. Lovie Whitaker (pers. comm.) pointed out to me that the situation could be compared to that of free-flying birds in a lighted room at night. Even if the doors and windows are open, the birds will not leave the lighted area to fly out into the dark. This is precisely the behavior I have observed at the Champaign tower. On the night of a kill, migrants often fly right through the tower framework and on out toward the edge of the lighted "room" around the tower, only to turn back again toward the light. Circling in this fashion some of them will inevitably strike the dark guys which support the tower."

A copy of this paper may be obtained online from the Searchable Ornithological Research Archive http://elibrary.unm.edu/sora/



Avery, M., Springer, P.F., & Cassel, J.F. 1976. The effects of a tall tower on nocturnal bird migration - A portable ceilometer study. Auk, 93, 281-291.

Reports results from a four year ceilometer study of birds flying in the vicinity of a 366-m tower in eastern North Dakota. Found that on overcast nights, significantly more birds were flying around the tower than at a site 305-m northeast of it and conversely that on clear nights significantly more birds were seen away from the tower than at it. This indicated that migrants actively avoided the structure on clear nights. Includes the an extensive discussion on the mechanism of towerkills and concurs with Graber's (1968) explanation for the towerkill phenomenon. The paper's summary section is quoted below.

"The results of a study of nocturnal migration during four migration seasons using a portable ceilometer at a 366-m tower in southeastern North Dakota were: On overcast nights significantly more migrants were seen at the tower than at a site 305-m northeast of it. Conversely, on clear nights significantly more birds were seen away from the tower than at it, which indicates that migrants actively avoided the structure on such nights. On non-overcast nights, the mean flight directions of migrants were similar at the tower and away from it, whereas the flight directions of birds seen on overcast nights tended to be more dispersed. Birds seen at the tower on overcast nights generally oriented themselves into the wind and remained close to the tower by fluttering or hovering. Birds did not circle the tower or orient toward the red tower lights. On two overcast nights, when hundreds of birds congregated at the tower, the migrants were at the tower both when the tower was transmitting and when it was not, which indicates that the signal transmitted by the tower had little, if any, role in migrants' congregating there. From these results, it is believed that on overcast nights, migrants are not attracted to tall lighted structures simply because celestial cues are unavailable. Rather, the refraction of light by moisture droplets in the air on cloudy nights greatly increases the illuminated space around a tower, and the migrants are arrested within a lighted area that they are reluctant to leave. As they mill about, collisions with the structure and other birds may result in mass mortality. To obtain a fuller understanding of this phenomenon and to develop means for preventing mortality of nocturnal migrants at towers, carefully designed experiments with various types of lights are necessary."

A copy of this paper may be obtained online from the Searchable Ornithological Research Archive http://elibrary.unm.edu/sora/



Larkin, Ronald P., and Barbara A. Frase. 1988. Circular paths of birds flying near a broadcasting tower in cloud. Journal of Comparative Psychology 102:90-93.

The first radar study of birds' circling behavior around towers -- documents its occurrence under low overcast and lack of occurrence under clear skies. The passage below is the paper's abstract.

"Tracks of birds migrating at night near an illuminated 308-m-tall broadcasting tower were recorded by using radar. During a period when low cloud surrounded the tower, birds flew in arcs or circles centered on the tower and having radii in excess of 100-m. Under clear skies or beneath cloud layers, arcs and circles were not observed. The data may contribute to understanding the behavioral mechanism of massive bird kills at tall lighted structures."



Gauthreaux, S. A., Jr., and C. G. Belser. 2006. Effects of artificial night lighting on migrating birds. In: Ecological Consequences of Artificial Night Lighting. (eds. C. Rich and T. Longcore), pp. 67-93. Covelo, California: Island Press.

The first published overview of the adverse affect of artificial light on birds in many years. Includes results of the authors' novel study using an image intensifier on the comparative bird flight behavior between a white-strobed tower, a tower with slow red flashing lights alternating with permanent red lights, and a control site with no lights. The authors found that more nonlinear flight occurred around the red-lit tower. The passage below is from the text of the paper.

"Migrating birds at the red light tower showed significantly more nonlinear and hovering flight than birds passing the strobe tower and flying over the control site, and it is likely that nonlinear flight behavior over time contributed to the concentration of migrants at the tower with red lights."



Evans, W. R., Y. Akashi, N. S. Altman, and A. M. Manville II. 2007. Response of night-migrating songbirds in cloud to colored and flashing light. North American Birds 60:476-488. Download PDF.

The first study to systematically document differences in the behavioral impact of different colors of light on songbirds in active night migration. The study also documented different behavioral responses in flashing light versus steady-burning light. In this study, red light was not found to induce aggregation behavior of night migrants but blue, green, and white light did. Flashing a white light that had induced aggregation led to no aggregation. This paper provides a detailed discussion on the possible mechanisms involved with bird aggregation in artificial light. The passage below is from the paper's conclusion.

"Our study shows that the color of light and whether it is steady-burning or flashing makes a significant difference in whether night-migrating birds exhibit aggregation behavior. We find no evidence that bird aggregation occurs because a light is red. While red light has been blamed for bird mortality at tall TV towers, our study indicates that for birds migrating within cloud cover, blue, green, or white light would be more likely to induce bird aggregation and associated mortality."



Longcore, T., Rich, C. and S. A. Gauthreaux, Jr. 2008. Height, Guy Wires, and Steady-burning Lights Increase Hazard of Communication Towers to Nocturnal Migrants: A Review and Meta-analysis. Auk 125(2):485-492.

The authors review the published scientific literature and unpublished reports with regard to the design features that influence mortality rates of migratory birds at communication towers (height, lighting, guy wires, and topographic position) and conducted a meta-analysis of studies of bird kills at towers to investigate the influence of tower height and guy wires on bird mortality.
Their review and analysis concludes that "avian mortality [at communications towers] would be reduced by restricting the height of towers, avoiding guy wires, using only red or white strobe-type lights as obstruction lighting, and avoiding ridgelines for tower sites."
A copy of this paper may be obtained in PDF format at http://www.urbanwildlands.org/Resources/Longcore_06-253.pdf



Gehring, J. Kerlinger, P. and A.M. Manville II. 2009. Communication towers, lights, and birds: successful methods of reducing the frequency of avian collisions. Ecological Applications, 19(2):505-514.

"To determine the relative collision risks that different nighttime Federal Aviation Administration (FAA) communication tower obstruction lighting systems pose to night-migrating birds, we compared fatalities at towers with different systems: white strobe lights only; red strobe-like lights only; red, flashing, incandescent lights only; and red, strobe-like lights combined with non-flashing, steady burning, red lights.. results suggest that avian fatalities can be reduced, perhaps by 50-71%, at guyed communication towers by removing non-flashing/steady-burning red lights.
 Our lighting change proposal can be accomplished at minimal cost on existing towers, and such changes on new or existing towers greatly reduce the cost of tower operation. Removing non-flashing lights from towers is one of the most effective and economically feasible means of achieving a significant reduction in avian fatalities at existing communication towers."
 



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