An Estimate of Avian Mortality at Communication Towers in the United States and Canada

Travis Longcore,Beau Macdonald,Albert M Manville,Sidney A Gauthreaux,Catherine Rich,Pierre Mineau,Daniel G Bert,David Drake,Michael L Avery,Erin Mutrie,Emilie R Travis,Lauren M Sullivan,Robert L Crawford,Martin Krkosek

doi:10.1371/journal.pone.0034025

Abstract

Avian mortality at communication towers in the continental United States and Canada is an issue of pressing conservation concern. Previous estimates of this mortality have been based on limited data and have not included Canada. We compiled a database of communication towers in the continental United States and Canada and estimated avian mortality by tower with a regression relating avian mortality to tower height. This equation was derived from 38 tower studies for which mortality data were available and corrected for sampling effort, search efficiency, and scavenging where appropriate. Although most studies document mortality at guyed towers with steady-burning lights, we accounted for lower mortality at towers without guy wires or steady-burning lights by adjusting estimates based on published studies. The resulting estimate of mortality at towers is 6.8 million birds per year in the United States and Canada. Bootstrapped subsampling indicated that the regression was robust to the choice of studies included and a comparison of multiple regression models showed that incorporating sampling, scavenging, and search efficiency adjustments improved model fit. Estimating total avian mortality is only a first step in developing an assessment of the biological significance of mortality at communication towers for individual species or groups of species. Nevertheless, our estimate can be used to evaluate this source of mortality, develop subsequent per-species mortality estimates, and motivate policy action.

Highlights

On the morning of September 11, 1948, ‘‘a good number of dead, dying, and exhausted birds’’ were found at the base of the WBAL radio tower in Baltimore, Maryland [1]
An estimate of the total number of birds killed at communication towers in the United States and Canada is relevant because the current transition from analog to exclusively digital broadcasting in the United States is expected to lead to the construction of more tall towers and a similar trend will likely follow in Canada
Tower Height–mortality Regression Towers used in the height–mortality regression were located throughout the eastern United States (Figure 2)

Summary

Introduction

On the morning of September 11, 1948, ‘‘a good number of dead, dying, and exhausted birds’’ were found at the base of the WBAL radio tower in Baltimore, Maryland [1]. Reports of such avian mortality at communication towers in North America became common in the 1950s [2,3,4,5,6,7]. Bats are killed in collisions with tall towers in unknown numbers [16,17,18].

Objectives

Methods

Results

Conclusion