Local avian density influences risk of mortality from window strikes.

Ann M Sabo,Ally S Lahey,Eric L Walters,Natasha D.G Hagemeyer

doi:10.7717/peerj.2170

Abstract

Up to a billion birds die per year in North America as a result of striking windows. Both transparent and reflective glass panes are a cause for concern, misleading birds by either acting as invisible, impenetrable barriers to desired resources, or reflecting those resources over a large surface area. A high number of window strikes occur during migration, but little is known about the factors of susceptibility, or whether particular avian taxa are more vulnerable than others. We report on a study of window strikes and mist-netting data at the Virginia Zoological Park (Norfolk, Virginia, USA), conducted in the autumn of 2013 and 2014. We focused on three factors likely to contribute to an individual’s predisposition to collide with windows: (i) taxonomic classification, (ii) age, and (iii) migrant vs. resident status. Thrushes, dominated by the partial migrant American Robin (Turdus migratorius), were significantly less likely to strike glass than be sampled in mist nets (χ2 = 9.21, p = 0.002), while wood-warblers (Parulidae) were more likely to strike than expected (χ2 = 13.55, p < 0.001). The proportion of juveniles striking windows (45.4%) was not significantly different (χ2 = 0.05, p = 0.827) than the population of juvenile birds naturally occurring at the zoo (48.8%). Migrants, however, were significantly more susceptible to window strikes than residents (χ2 = 6.35, p = 0.012). Our results suggest that resident birds are able to learn to avoid and thus reduce their likelihood of striking windows; this intrinsic risk factor may help explain the apparent susceptibility of certain taxa to window strikes.

Highlights

Building collisions are a major anthropogenic threat to many avian taxa, with the best estimates of mortality ranging between 365 to 988 million individuals killed annually in the United States (Loss et al, 2014)
We investigated two main hypotheses of window strike susceptibility: Hypothesis 1—Taxon-specific susceptibilities to fatal window collisions are likely to occur due to intrinsic factors
Because avian density increases relative to quality of vegetation and resources, these high quality areas generally have a higher number of window collisions (Klem, 1989)

Summary

Introduction

Building collisions are a major anthropogenic threat to many avian taxa, with the best estimates of mortality ranging between 365 to 988 million individuals killed annually in the United States (Loss et al, 2014). How to cite this article Sabo et al (2016), Local avian density influences risk of mortality from window strikes. Recent meta-analyses of window strike data have found strong support for increased species-specific risk to fatal window collisions when accounting for overall population abundances and species ranges, with migratory taxa being vulnerable (Arnold & Zink, 2011; Loss et al, 2014). Without accounting for local densities, these apparent species-specific vulnerabilities may still be a result of local population density rather than true vulnerability (Kahle, Flannery & Dumbacher, 2016), one recent study found that adult birds were less likely to hit windows despite proportionally higher abundance during the summer breeding season (Hager & Craig, 2014)

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Conclusion