Transactions of the Illinois State Academy of Science received 1/17/13 (2013) Volume 106, pp. 9-12 accepted 8/12/13

The Effects of Tower Structure and Weather Conditions on Avian Mortality at Three Television Towers in Central Illinois

Lisa A. Lundstrom1, David Joseph Horn1*, and Angelo P. Capparella2 1Department of Biology, Millikin University, 1184 W. Main St., Decatur, IL 62522, USA 2School of Biological Sciences, Campus Box 4120, Illinois State University, Normal, IL 61790, USA *Correspondence: [email protected]

ABSTRACT

Avian mortality has been documented at television towers and other constructed lighted structures for over 150 years, and it is estimated that 6.8 million birds are killed annually in the United States and Canada as a result of communication towers. Tower structure (lighting, height, and guy wires) and weather conditions (wind direction, cloud cover) play a large role in mortality rates. We examined the effects of tower structure and weather conditions on mortality at three television towers in central Illinois (WAND, WBUI, and WILL). For- ty-three searches were conducted between August and November 2006-2009 with a total of 415 birds from 14 families found. Most birds found were of Family Parulidae (66%), Family Emberizidae (9%), and Family Turdidae (9%). The WILL tower accounted for 96% of the total birds killed. The high mortality observed at the WILL tower may be due to the tower’s steady and flashing red lights as opposed to the flashing white lights on the WAND and WBUI towers. We found that more birds were killed following nights with winds from the north and ≥50% cloud cover. Most studies of tower collisions have focused on tower structure rather than weather conditions; however, the combination of tower lighting and weather may play a substantial role in avian mortality.

INTRODUCTION lights instead. Previous studies have found fatalities than towers of the same height Avian mortality associated with artificial that nocturnally migrating birds would fly without guy wires. lighting on human structures is thought to around standard FAA lights of communi- While birds can collide with towers on be a significant source of human-caused cation towers until the lights were turned clear nights, previous studies have found bird death (Evans 2007). The most recent off (Cochran and Graber 1958; Avery et al. that larger numbers of birds are killed on mortality estimate at communication tow- 1977). fall nights with heavy cloud cover, north- ers is 6.8 million birds per year in the Unit- While the exact cause of this attraction erly winds, and a low cloud ceiling when ed States and Canada; about 50% greater is unknown, it is thought that migrating they do not have the stars to navigate by than the current estimate by the U.S. birds use both visual cues, such as stars, (Avery et al. 1977; Seets and Bohlen 1977; Fish and Wildlife Service (Longcore et al. as well as an internal magnetic compass to Larkin and Frase 1988; Kruse 1996). These 2012). Past studies have found that almost navigate, and the artificial lighting some- conditions force birds to fly at lower alti- 95% of all birds that collide with lighted how interferes with this (Gauthreaux and tudes within the range of towers, exposing structures are neotropical migrants, par- Belser 2006). For example, laboratory tests them to tower structure risks. ticularly Family Parulidae (i.e. warblers; have suggested that the internal magnetic We examined how the number of birds Longcore et al. 2013). The main factors compass may be wavelength-dependent, killed at one class of communication tow- associated with tower kills are tower struc- with birds showing good orientation un- er, tall television towers, was influenced by ture (lighting, height, and guy wires) and der white and green lights (Wiltschko and tower structure as well as cloud cover and weather conditions (Longcore et al. 2008; Wiltschko 1995) and disorientation under prevailing winds during fall migration. Gehring et al. 2009). red light (Wiltschko et al. 1993). While there have been many studies on Artificial lighting affects the behavior of In the presence of lighted towers, birds the effects of tower structure, fewer studies many plant and animal species, particular- generally follow a circular, curvilinear have examined the role of specific weather ly at night (Rich and Longcore 2006). Spe- flight pattern, and will continually circle conditions on the number of bird colli- cies can be attracted to, or disoriented by, around them until they collide with some sions (although see Longcore et al. 2012). sources of artificial light through positive part of the tower or its guy wires, or suc- We predicted that birds would experience phototaxis (Verheijen 1985; Longcore and cumb to exhaustion and can no longer fly the greatest mortality during nights with Rich 2004). This behavior in birds has been (Gauthreaux and Belser 2006). In an ex- ≥50% cloud cover and predominantly documented at communication towers for amination of the role of tower height and northerly winds. By understanding the over 50 years as a result of the lighting sys- guy wires on avian mortalities, Gehring et effects of weather and tower structure on tems required by the Federal Aviation Ad- al. (2011) found that there are 54—86% mortality, we can make recommendations ministration (FAA) (Gehring et al. 2009). fewer fatalities at medium height, guyed on ways to reduce avian mortality at tele- Standard FAA lighting normally consists towers (116—146 m) than at tall height, vision towers. of a combination of steady and flashing guyed towers (>305 m) and that guyed METHODS red lights, although some towers use white towers account for 16 times more bird We conducted our study at three television The Effects of Tower Structure and Weather Conditions on Avian Mortality at Three Television Towers in Central Illinois 10 Lisa A. Lundstrom, David Joseph Horn, and Angelo P. Capparella towers in central Illinois between August Table 1. Characteristics of three television towers and the landscape that surrounded each and November 2006—2009. The location of in central Illinois. the towers were as follows: 1) WAND-TV Chacteristic WILL WAND WBUI tower, Macon Co.: Whitmore Twp. (T17N, Tower Variables R3E, S11), ca 2¼ mi. NE Oreana; 2) WBUI- a TV tower, Macon Co.: Whitmore Twp. Tower Height 282 m 379 m 390 m (T17N, R3E, S11), ca 2 mi. NE Oreana; Number of Wires 27 24 24 and 3) WILL-TV tower, Piatt Co.: Willow Guy-Wire Length 6202 m Not determinedb 5538 m Branch Twp. (T18N, R5E, S67/8), ca 5½ mi. Number of Flashing Lights 3 13 13 W Monticello. Number of Steady Lights 12 0 0 The towers were searched for carcasses Light-Pulse Frequency 30/min 40/min 40/min on mornings following nights with four Light Color Red White White weather conditions: 1) ≥50% cloud cover Construction Color Red/White Steel Steel and northerly winds, 2) ≥50% cloud cover and non-northerly winds, 3) <50% cloud Landscape Variables cover and northerly winds, and 4) <50% Ground Elevation 210 m 209 m 208 m cloud cover and non-northerly winds. Distance to Water Source 5.7 km 4.1 km 4.1 km Nights were classified using hourly weath- Distance to City 9.7 km 8.9 km 8.9 km er observations from http://www.wunder a Tower height and ground elevation were obtained from http://www.fccinfo.com. ground.com. To determine which morning b The exact guy-wire length could not be determined; however, the tower construction of WBUI and to look for birds, we a priori selected days WAND is nearly identical. Therefore, we expect the guy-wire length to be similar. to search at the beginning of the fall sea- son. To balance the number of searches by weather condition category, we did addi- ed. Birds collected were deposited at the than 50 birds, the first on 4 October 2006 tional searches specific to those categories J.W. Powell-D. Birkenholz Natural History with 275 birds found, and the second on 28 by monitoring conditions the previous eve- Collection at Illinois State University. October 2009 with 60 birds found. ning and searching for birds that morning. Searches began at dawn to reduce carcass We collected characteristics of each tower We found that the number of birds killed loss to scavengers (Crawford 1971). that could influence collision frequency. was not equivalent in each of our four These included tower height, number of weather categories (Fig. 1, X2=33.3, P<0.05). At each of the three television towers, we wires, guy-wire length, number of lights, The majority of our birds were found fol- first searched the paved and grassy areas light-pulse frequency, light color, tower col- just outside the tower facility. We then en- or, ground elevation, and distance to near- tered the facility and searched around the est water source and city. Distance charac- tower, including the roof. The areas under teristics of each tower were measured using Table 2. The number of birds found from the guy wires were searched after harvest by an Opti-Logic Laser Rangefinder. each of 14 familes at 3 television towers in walking straight paths from the tower base central Illinois from 2006-2009. We determined whether the number of to the base of the three sets of guy wires Family Number of Fatalities and back, encompassing approximate- dead birds collected per night was equiva- Parulidae 272 ly 5 m to each side of the guy wires. Not lent among our four weather categories us- searched was the extensive area between ing a chi-square test. A P-value of <0.05 was Turdidae 38 the guy wires. The area searched was sim- considered statistically significant. Emberizidae 38 ilar between towers. However, because of RESULTS Vireonidae 23 differences in when crops were harvested, Regulidae 13 some towers may have been searched more Tower characteristics varied among our Troglodytidae 6 extensively than others on certain visits. three towers (Table 1). In particular, tower Nevertheless, the similarity in height and height and lighting differed between WILL, Cardinalidae 5 guy wire lengths among the towers should WAND, and WBUI. Icteridae 5 not result in significant bias in the number Mimidae 5 Forty-three searches were made between of dead birds found at each tower (Table 1). Certhiidae 2 Carcasses that were not decomposed, based August and November 2006—2009. We on the recession of the eyeballs, were trans- found 415 birds from 14 families at the Picidae 2 ported to Millikin University for identifica- three towers, with the most birds from Tyrannidae 2 tion and further processing. For each bird Family Parulidae (Table 2, n=272). The Unidentified 2 WILL tower had the most kills (n=397), collected, the date; tower; species; colors of Cuculidae 1 the iris, maxilla, mandible, tarsi, and toes; followed by WAND (n=14), and WBUI Sturnidae 1 and any other general remarks were record- (n=4). We recorded two kills with greater The Effects of Tower Structure and Weather Conditions on Avian Mortality at Three Television Towers in Central Illinois 11 Lisa A. Lundstrom, David Joseph Horn, and Angelo P. Capparella

with the number of guy wires present, but guy wires correlate with height (Longcore et al. 2008; Gehring et al. 2011). While our shorter tower (by 93 m) had more guy wires, it was only one more guy wire per group than each of the other two towers. Given the dramatic effect recorded for solid versus flashing lights (Gehring et al. 2009) and small difference in guy wire number, it is most likely that the lighting system of the WILL tower had a larger effect on mortality rates. We found that more birds were killed fol- lowing nights with ≥50% cloud cover and northerly winds, with our two largest kills occurring under these conditions at WILL. Longcore et al. (2008), through a meta-anal- Fig. 1. The number of fatalities differed among weather conditions. More birds were found ysis of over 20 towers, found that the largest following nights with ≥50% cloud cover and northerly winds compared to other condi- 2 kills occurred on nights with heavy cloud tions (X =33.3, P<0.05). cover in the presence of a combination of steady and flashing red lights. This suggests that while both weather and lighting play a lowing nights with ≥50% cloud cover and strobes, although the white strobes did have large role separately, it is the combination northerly winds, with 304 individuals col- an effect on flight patterns. of the two that may be most important. lected (73%). The nights that accounted for the second highest number of birds collect- Gehring et al. (2009) examined mortality While previous studies have reported high- ed were nights with ≥50% cloud cover and rates between towers similar in construc- er kills following nights with heavy cloud non-northerly winds, with 98 individuals tion, with different lighting systems. They cover (Avery et al. 1977; Crawford 1981; collected (24%). attempted to determine whether mortality Larkin and Frase 1988), examinations of rates differed among towers equipped with the combination of cloud cover and wind DISCUSSION flashing lights of various types and col- direction could be tested more rigorously. ors only versus towers equipped with the Most of our birds (73%) were found fol- Sixty-six percent of the birds found were FAA standard combination of steady and lowing nights with ≥50% cloud cover with members of Family Parulidae (i.e., war- flashing red lights. They found that more the presence of northerly winds. This sug- blers). Longcore et al. (2013) combined birds were killed at towers with steady and gests that northerly winds in addition to mortality data from previous studies to es- flashing red lights compared to towers with heavy cloud cover create the most deadly timate mortality by species, and estimated only white, flashing strobes; red, strobe-like conditions. However, in our study an ad- that of the over 5,200,000 birds recorded, lights; and red, flashing, incandescent lights ditional 24% of birds were killed on nights Family Parulidae accounted for 3,075,659 (Gehring et al. 2009). Thus, the steady and with heavy cloud cover and non-northerly (58.4%). While a smaller percentage than flashing red lights on the WILL tower may winds. Previous studies have concluded ours, warblers had the highest mortality of explain why we observed 96% of our total that while more birds are killed following any family-specific category. kills at that location. nights with northerly winds than nights with non-northerly winds, overcast nights Both of our large kills occurred at the WILL A correlation has been documented be- tower, which has steady and flashing red consistently experience mortality events tween tower height and mortality rates regardless of wind direction (Avery et al. lighting. Gauthreaux and Belser (2006) for towers with the same lighting scheme compared bird flight patterns near towers 1977; Crawford 1981; Larkin and Frase (Longcore et al. 2008; Gehring et al. 2011; 1988). with steady and flashing red lights, towers Longcore et al. 2012). Our shorter tower with only white strobes, and a control tow- experienced greater mortality than the two Our estimates of mortality should be con- er, which was unlit. They found that birds taller towers combined, but it had a differ- sidered minimum values, as there were flew in straight paths over the control area, ent lighting scheme and more guy wires. some possible sources of error in our study. while birds flew in curvilinear paths and The WILL tower has more guy wires per We began our searches at dawn to lower congregated near lighted towers. Between group and a combination of steady and the impact of scavengers, which can greatly the two lighting categories used, they found flashing red lights, while the WBUI and reduce the number of carcasses (Crawford that birds congregated in much higher WAND towers have fewer guy wires per 1971). However, it is possible some car- numbers at towers lit with steady and flash- group and flashing white lights. Studies casses were taken before we were able to ing red lights than towers lit with white have found that avian mortality increases collect them. We did not search the area be- The Effects of Tower Structure and Weather Conditions on Avian Mortality at Three Television Towers in Central Illinois 12 Lisa A. Lundstrom, David Joseph Horn, and Angelo P. Capparella tween the guy wires, and thus, some birds We thank R. Buis, K. Collins, M. Huschen, D.G. Bert, L.M. Sullivan, E. Mutrie, S.A.Gauth- will have been missed. In addition, we did J. Gibson, C. Matthews, Q. Murray, and J. reaux Jr., M.L. Avery, R.L. Crawford, A.M. not determine searcher efficiency. Finally, Partlow for their assistance collecting data. Manville II, E.R. Travis, and D. Drake. 2012. differences in harvest times between both Funding for this study was provided by the An estimate of avian mortality at communica- tion towers in the United States and Canada. tower sites and seasons meant that some Champaign County Audubon Society, De- PLoS ONE 7(4):e34025. doi:10.1371/journal. towers were searched more extensively catur Audubon Society, and the Millikin pone.0034025. than others on some visits. University Fund for Ornithological Re- Longcore, T., C. Rich, P. Mineau, B. MacDonald, search. D.G. Bert, L.M. Sullivan, E. Mutrie, S.A.Gauth- There are three main solutions to reduce reaux Jr., M.L. Avery, R.L. Crawford, A.M. avian mortality at television towers. The LITERATURE CITED Manville II, E.R. Travis, and D. Drake. 2013. first would be to reduce tower height, as Arnold, T.W. and R.M. Zink. 2011. Collision Avian mortality at communication towers in mortality risk increases exponentially with mortality has no discernible effect on pop- the United States and Canada: which species, height (Longcore et al. 2012). The second ulation trends of North American birds. how many, and where? Biol. Conserv. 158:410- solution is to reduce or eliminate the num- PLoS ONE 6(9):e24708. doi:10.1371/journal. 419. ber of guy wires. Since guy wires account pone.0024708. Rich, C. and T. Longcore. 2006. Ecological con- for the majority of bird kills due to the Avery, M., P.F. Springer, and J.F. Cassel. 1977. sequences of artificial night lighting. Island circling behavior of birds in the presence Weather influences on nocturnal bird mor- Press, Washington, D. C. tality at a North Dakota tower. Wilson Bull. Seets, J. W. and H.D. Bohlen. 1977. Comparative of tower lights, removing them could re- 89:291-299. mortality of birds at television towers duce collision rates (Brewer and Ellis 1958; Brewer, R. and J.A. Ellis. 1958. An analysis of in central Illinois. Wilson Bull. 89:422-433. Kruse 1996), but it is not possible for towers migrating birds killed at a television tower Taylor, W.K. 1981. No longer a big killer. Florida > 300 m (Longcore et al. 2012). Thus, while in east-central Illinois, September 1955-May Naturalist 54:4-10. these two solutions will lower mortality 1957. Auk 75:400-414. Verheijen, F.J. 1985. Photopollution: artificial rates, they are unlikely to happen, especial- Cochran, W.W. and R.R. Graber. 1958. Attrac- light optic spatial systems fail to cope with ly for towers that are already constructed. tion of nocturnal migrants by lights on a incidents, causations, remedies. Exp. Biol. television tower. Wilson Bull. 70:378-380. 1985:1-18. The third solution is a change in tow- Crawford, R.L. 1971. Predation on birds killed at Wiltschko, W., U. Munro, H. Ford, and R. Wiltsc- er lighting systems. Gehring et al. (2009) TV tower. Oriole 36:33-35. hko. 1993. Red light disrupts magnetic orien- mainly suggested the removal of non-flash- Crawford, R.L. 1981. Weather, migration and tation of migratory birds. Nature 364:525-527. ing red lights leaving only the flashing red autumn bird kills at a north Florida TV tower. Wiltschko, W. and R. Wiltschko. 1995. Migra- Wilson Bull. 93:189-195. tory orientation of European Robins is affected strobe, but recommended a color change Evans, W.R. 2007. Response of night-migrating by the wavelength of light as well as a magnetic to white strobes as well. Taylor (1981) re- songbirds in cloud to colored and flashing pulse. J. Comp. Phys. A 177:363-369. corded a drastic reduction in fatalities at a light. North American Birds 60:476-488. Florida tower when the lighting system was Gauthreaux, S., Jr. and C. Belser. 2006. Effects changed from steady and flashing red lights of artificial night lighting on migrating birds. to white strobe lights. Pages 67-93 in Ecological consequences of ar- tificial night lighting (C. Rich and T. Longcore, Arnold and Zink (2011) suggest that while Editors). Island Press, Washington D.C., USA. millions of birds are killed by collisions, Gehring, J., P. Kerlinger, and A.M. Manville not only with communication towers but II. 2009. Communication towers, lights, and with other constructed structures, it may birds: successful methods of reducing the fre- not have a significant effect on population quency of avian collisions. Ecol. Appl. 19:505- trends. However, mortality rates are not the 514. Gehring, J., P. Kerlinger, and A.M. Manville II. same for all species (Longcore et al. 2013). 2011. The role of tower height and guy wires Longcore et al. (2013) found that some on avian collisions with communication tow- species, including U.S. Fish and Wildlife ers. J. Wildlife Manage. 75:848-855. Service Birds of Conservation Concern, Kruse, K. 1996. A study of the effects of trans- are suffering losses of several percent of mission towers on migrating birds. Thesis. their estimated population size. Because of University of Wisconsin, Green Bay, USA. the differences in mortality rates between Larkin, R. and B. Frase. 1988. Circular paths of species, Longcore et al. (2013) suggest per birds flying near a broadcasting tower in cloud. species estimates are undertaken for all hu- J. Comp. Psychol. 102:90-93. Loncore, T. and C. Rich. 2004. Ecological light man-caused sources of avian mortality. pollution. Front. Ecol. Environ. 2:191-198. ACKNOWLEDGMENTS Longcore, T., C. Rich, and S.A. Gauthreaux. 2008. Heights, guy wires, and steady-burning We thank the television stations for giving lights increase hazard of communication tow- us permission to conduct this research. We ers to nocturnal migrants: a review and me- ta-analysis. Auk 125:485-492. thank the Illinois Department of Natural Longcore, T., C. Rich, P. Mineau, B. MacDonald, Resources for providing salvage permits.