Nocturnal flight-calling behaviour predicts vulnerability to artificial light in migratory birds.

Benjamin M Winger,David E Willard,Andrew W Jones,Mary Hennen,Andrew Farnsworth,Brian C Weeks

doi:10.1098/rspb.2019.0364

Abstract

Understanding interactions between biota and the built environment is increasingly important as human modification of the landscape expands in extent and intensity. For migratory birds, collisions with lighted structures are a major cause of mortality, but the mechanisms behind these collisions are poorly understood. Using 40 years of collision records of passerine birds, we investigated the importance of species' behavioural ecologies in predicting rates of building collisions during nocturnal migration through Chicago, IL and Cleveland, OH, USA. We found that the use of nocturnal flight calls is an important predictor of collision risk in nocturnally migrating passerine birds. Species that produce flight calls during nocturnal migration tended to collide with buildings more than expected given their local abundance, whereas those that do not use such communication collided much less frequently. Our results suggest that a stronger attraction response to artificial light at night in species that produce flight calls may mediate these differences in collision rates. Nocturnal flight calls probably evolved to facilitate collective decision-making during navigation, but this same social behaviour may now exacerbate vulnerability to a widespread anthropogenic disturbance. Our results also suggest that social behaviour during migration may reflect poorly understood differences in navigational mechanisms across lineages of birds.

Highlights

The nearest that we can usually come to observing the flight itself is to stand out in the open on some starlit night and listen to the faint chirps that come floating down from the great vault above
We investigate the importance of flight calls as potential social cues for collective decision-making among nocturnally migratory passerine birds by examining the relationship between flight calling and behavioural responses to a disruptive stimulus: artificial light at night (‘artificial light’)
Previous studies found that the rate of flight calling among nocturnal migrants increased around artificial light [27,34], highlighting an interaction between light-induced disorientation and social communication during migration

Summary

Introduction

The nearest that we can usually come to observing the flight itself is to stand out in the open on some starlit night and listen to the faint chirps that come floating down from the great vault above. Our empirical understanding of collective migratory behaviour is lacking, among species whose social behaviour is not observed during migration Nowhere is this knowledge gap starker than in nocturnally migrating species that are hidden from human view during their passage [8,9]; one of the greatest barriers to researching bird migration is that many bird species migrate at night, making direct observation of migrating individuals difficult. Technologies such as radar [10,11], ceilometers [8], thermal imaging cameras [12] and tracking

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