HEIGHT, GUY WIRES, AND STEADY-BURNING LIGHTS INCREASE HAZARD OF COMMUNICATION TOWERS TO NOCTURNAL MIGRANTS: A REVIEW AND META-ANALYSIS

Abstract

Communication towers in North America kill millions of birds annually, and most of these are Neotropical species that mi-grate at night (Banks 1979, Shire et al. 2000). Estimates of total annual mortality in the United States are about 4–5 million to an order of magnitude greater (U.S. Fish and Wildlife Service [US-FWS] 2000, Erickson et al. 2005). In 2000, the USFWS proposed guidelines to minimize avian collisions with communication tow-ers. In November 2006, the Federal Communications Commis-sion (FCC) announced a " notice of proposed rulemaking " that sought input on a proposal to require changes to tower design to reduce avian mortality. Here, we review and analyze the literature on the features of towers that can be regulated, particularly tower design and placement, to provide a scientific basis for regulation of tower construction and operation. We prepared an earlier version of this review (Longcore et al. 2005) for the American Bird Con-servancy and other conservation groups in response to a " notice of inquiry " issued by the FCC in 2003 to gather information on colli-sions between birds and communication towers. The ornithological literature contains frequent reports of birds killed at lights (see references in Weir 1976, Avery et al. 1980, Kerlinger 2000, Gauthreaux and Belser 2006). Two long-term studies with periodic searches confirmed that large numbers of birds can be killed at communication towers: (1) a 38-year study of a single 305-m television tower in west central Wisconsin docu-mented 121,560 birds of 123 species killed (Kemper 1996), and (2) a 29-year study at a Florida television tower documented the deaths of 44,007 birds of 186 species (Crawford and Engstrom 2001). Be-cause the FCC does not require monitoring of avian mortality at towers that it registers or otherwise approves, and because tower operators do not monitor mortality, bird kills reported in the lit-erature represent only a minimum measurement of total mortal-ity. Most sites are never visited to find dead birds, and most of those that are surveyed are visited only sporadically. Despite a number of useful reviews of the topic (Weir 1976, Avery et al. 1980, Trapp 1998, Kerlinger 2000) and recent progress on key issues such as the influence of lighting type and tower height (e.g., Jones and Francis 2003, Gauthreaux and Belser 2006, Gehring et al. unpubl. data), an analytical synthesis of factors influencing avian mortality at towers would aid policy development and focus future research. Here, we ask how design and placement of towers affect mortality of birds. Many variables influence rates of bird mortality at communication towers; certain types of weather conditions (e.g., frontal systems) are implicated in most large kills (see review in Gauthreaux and Belser 2006). Inclement weather and other physical variables, such as the effects of the lunar cycle, are beyond the control of regu-lators. Therefore, we concentrate on the elements of tower design that can influence bird mortality and that can be regulated.