The influence of artificial night at night and polarized light on bird-building collisions

Sirena Lao, Bruce A. Robertson, Abigail W. Anderson, Robert B. Blair, Joanna W. Eckles, Reed J. Turner, Scott R. Loss

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Collisions with buildings annually kill up to 1 billion birds in the United States. Bird-building collisions primarily occur at glass surfaces: birds often fail to perceive glass as a barrier and appear to be attracted to artificial light emitted from windows. However, some aspects of avian vision are poorly understood, including how bird responses to different types of light influence building collisions. Some evidence suggests birds can detect polarized light, which may serve as a cue to assist with migration orientation and/or detect water bodies. Dark, reflective surfaces, including glass, reflect high degrees of polarized light, causing polarized light pollution (PLP). However, no studies have analyzed the relationship between bird collisions and PLP reflected from buildings. Additionally, while artificial light at night (ALAN) is frequently implicated as a major factor influencing bird-building collisions, few studies have analyzed this relationship. We investigated both types of light pollution—PLP and ALAN—and their association with bird collisions at 48 façades of 13 buildings in Minneapolis, Minnesota, USA. We found that the area of glass emitting ALAN was the most important factor influencing collisions, and that this effect of ALAN was independent of overall glass area; this result provides strong support for turning off lights at night to reduce bird-building collisions. Although we found no relationship between PLP and collisions, additional research is needed to better understand bird responses to polarized light. Fully understanding how different aspects of light influence bird-building collisions can inform conservation efforts to reduce this major threat to birds.

Original languageEnglish (US)
Article number108358
JournalBiological Conservation
StatePublished - Jan 2020

Bibliographical note

Funding Information:
This study was supported by Minnesota Sports Facilities Authority and Minnesota Vikings Football, LLC . Funders were not involved in the study design, data collection, analysis, interpretation, or writing and submission of the manuscript. Appendix A Table A1 Results of likelihood ratio test (LRT) with single-term deletions of polarized light and artificial night lighting variables. Differences in AIC values between the full model (“None”) and other models represent the change in AIC associated with dropping the variable from the full model; thus, higher AIC values represent greater reduction in model support with exclusion of the focal variable. Beta coefficients and 95% confidence intervals to illustrate direction of effect are from the full additive negative binomial GLMM with building as a random effect and number of surveys as an offset term. Table A1 Variable dropped AIC LRT p (chi) β 95% CI None 295.06 Polarization index 293.09 0.0331 0.85571 −0.001 −0.012–0.010 Maximum polarization 293.15 0.0879 0.76683 −0.001 −0.009–0.007 Minimum polarization 294.46 1.3980 0.23706 0.008 −0.002–0.018 Lighting proportion 299.63 6.5709 0.01037 0.012 0.004–0.021 Lighting area 315.89 22.8270 1.773e-06 0.022 0.015–0.030


  • Artificial light at night
  • Avian mortality
  • Bird-building collisions
  • Bird-window collisions
  • Light pollution
  • Polarized light

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