Collision Mortality Has No Discernible Effect on Population Trends of North American Birds

Todd W Arnold,Robert M Zink,Brock Fenton

doi:10.1371/journal.pone.0024708

Todd W Arnold, Robert M Zink + Show 1 more

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https://doi.org/10.1371/journal.pone.0024708

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Abstract

Avian biodiversity is threatened by numerous anthropogenic factors and migratory species are especially at risk. Migrating birds frequently collide with manmade structures and such losses are believed to represent the majority of anthropogenic mortality for North American birds. However, estimates of total collision mortality range across several orders of magnitude and effects on population dynamics remain unknown. Herein, we develop a novel method to assess relative vulnerability to anthropogenic threats, which we demonstrate using 243,103 collision records from 188 species of eastern North American landbirds. After correcting mortality estimates for variation attributable to population size and geographic overlap with potential collision structures, we found that per capita vulnerability to collision with buildings and towers varied over more than four orders of magnitude among species. Species that migrate long distances or at night were much more likely to be killed by collisions than year-round residents or diurnal migrants. However, there was no correlation between relative collision mortality and long-term population trends for these same species. Thus, although millions of North American birds are killed annually by collisions with manmade structures, this source of mortality has no discernible effect on populations.

Highlights

Habitat destruction, overexploitation, climate change and the creation of manmade obstacles have been identified as the major threats to migrating animals [1], especially birds [2,3,4]
Migrant birds were at greater risk of collision mortality with buildings and towers, our analyses suggest that this conspicuous source of mortality has had no discernible effect on long-term population dynamics among North American landbirds, and this finding was robust to all of the statistical adjustments that we employed
Collision mortality could be described as an added burden for populations already in decline for other reasons, and our list of super colliders (Table S1) includes two such species: golden-winged warbler and Bachman’s sparrow, but the list of super colliders includes two species that are increasing significantly [15]

Summary

Introduction

Overexploitation, climate change and the creation of manmade obstacles have been identified as the major threats to migrating animals [1], especially birds [2,3,4]. For North American birds, the major anthropogenic sources of mortality include predation by house cats, poisoning, and collisions with windows, communication towers, high-tension wires and motor vehicles [7]. Evans Ogden [8] estimated that 70% of migrant birds in eastern North America migrate through at least one major metropolitan area during each migration event. Nocturnal migrants frequently collide with skyscrapers after becoming disoriented by building lights, especially during inclement weather [8], and birds making migratory stopovers in urban areas are especially prone to collision with lowlevel windows as they forage in unfamiliar environments [8,9,10]. Eastern North America has .60,000 communication towers .60m tall and documented kills of migratory birds at individual towers have ranged from 80 to 3,200 birds per year [7,11]

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