Birds that use flight calls are more likely to crash into buildings

Illuminated city buildings present a major collision risk for birds that migrate at night. Now, a new study has found that birds who use chirps called flight calls to help navigate are more likely to collide with lighted buildings compared to other migrating birds that don’t produce such calls.

The study was conducted by researchers from the University of Michigan and relied on decades of data from the Field Museum in Chicago.

While flight calls can be useful to help migrating birds stay on course, the results of the study show that these calls may be inadvertently luring more birds to their death when some migrating birds become disoriented and head towards sources of artificial light.

“Nocturnal flight calls likely evolved to facilitate collective decision-making among birds during navigation, but this same social behavior may now exacerbate vulnerability to a widespread anthropogenic disturbance: artificial light from buildings,” said Benjamin Winger, the first author of the study.

The research was published in the journal Proceedings of the Royal Society B.

Monitoring efforts in cities like Chicago and Cleveland have helped reduce instances of bird collisions, but this study shows that bird calls as a collision risk factor have been overlooked and that more can still be done in cities to limit bird deaths.

“To date, we have not mined the potential information that flight calls could provide to advance our understanding of how nocturnally migrating birds make decisions and orient in difficult situations,” said Andrew Farnsworth, a co-author of the research. “This work heralds a new direction in the integration of data on collisions, species distributions and behavior ecology for understanding nocturnal bird migration.”

The researchers analyzed data on 70,000 nighttime songbird collisions in Chicago and Cleveland dating back to 1978.

The data was collected from Field Museum researchers and volunteers in Chicago and Cleveland and included information on 93 species of birds.

For the study, the researchers focused on the relationship between high-frequency flight calls from songbirds like warblers, sparrows, and thrush and nighttime collisions.

The majority of bird species in the collision database were songbirds that use flight calls. There were far fewer collisions involving birds that didn’t use calls while flying.

“Our paper provides some of the strongest published evidence on the effect of artificial light on bird collisions in urban areas, though this relationship has been known anecdotally for a long time,” said Benjamin Wing, the first author of the study. “This relationship may spawn a vicious cycle of increased mortality rates if disoriented individuals lead other migrating individuals to sources of artificial light.”

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By Kay Vandette, Earth.com Staff Writer