Revisiting the Classics: What factors influence the start of the dawn chorus of House Wrens?

Sharon Gill, Erin Grabarczyk, and Maarten Vonhof

Linked paper: Social factors, not anthropogenic noise or artificial light, influence onset of dawn singing in a common songbird by C.J. Stuart, E.E. Grabarczyk, M.J. Vonhof, and S.A. Gill, The Auk: Ornithological Advances.

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A House Wren sings at its nest box. Photo by Erin Grabarczyk.

One of the daily joys of summer is waking to the sounds of bird song. Those early morning bursts of singing herald the start of our days, for birds and people alike. If we listen carefully, though, the dawn chorus also reveals something about the state of nature. We might channel Rachel Carson and, based on when birds start to sing each morning, consider what they are telling us about their environment.

What might birds tell us? Historically, they might have told us that cool temperatures on cloudy nights delayed the start of dawn singing. Or that female breeding partners were fertile and males were guarding them closely, either by singing more and earlier or singing less and later depending on the particular species. Today, birds might tell us about how they react to changes in their environment: do they sing earlier when the night sky is brighter, or later if it’s noisier at night, at dawn, or throughout the day?

It was the latter question that initially motivated us and led undergraduate Carley Stuart to do her honors thesis research on whether artificial light and human-caused noise affect the daily onset of the dawn chorus. But given the classic research that shows social context also modifies onset of singing, we considered the role of social factors such as the number of competitors or the mate’s fertility on the start of singing as well. We studied a common songbird, the House Wren, which breeds in nature preserves as well as urban environments. Our ongoing research on this species has found that males alter the structure of their songs and their responses to intruders under noisy conditions, but also that social context matters too. By considering anthropogenic influences and social context together, we hoped to get a broad perspective on the onset of the dawn chorus.

With these questions in mind, we headed to our field sites, positioning autonomous sound recorders at nest boxes to record the onset of singing by male House Wrens and ambient noise levels and using light meters to record sky brightness. We also color-banded and monitored the breeding activities of males, documenting their complex social lives.

We were glad we took this broader perspective. House Wrens began singing around civil twilight, when the sun was just starting to brighten the night sky. We found that it was social factors, not anthropogenic influences, that affected when males began to sing. More neighbours? Sing earlier. Nest building or fertile mate? Sing earlier. More noise and artificial light? Don’t change the timing of the dawn chorus. In regards to when males start their day, our research told us that House Wrens don’t appear to be bothered by artificial light and noise.

We were surprised by this result, as other species that begin dawn singing at similar times of day as House Wrens do sing earlier with brighter skies and more noise. Also, our previous studies have shown that noise affects male House Wrens in other ways, changing how they sing and how they interact with intruders. This makes our job of listening more complicated, as it means that just because one aspect of a bird’s life isn’t affected by human-generated environmental change doesn’t mean birds aren’t affected in other ways. That is a humbling prospect at this time of rapid environmental change and threats to our natural world. It means we need more information and broad assessments to fully understand the responses of animals to changing environments. We need to listen even more carefully.

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