Famously, the use of caged birds to alert miners to the invisible dangers of gases such as carbon monoxide gave rise to the cautionary metaphor “canary in a coal mine.”
But other than the fact that exposure to toxic gases in a confined space kills caged birds before affecting humans — providing a timely warning to miners — what do we know about the effects of air pollution on birds?
Not as much as you’d think, according to researchers from the University of Wisconsin-Madison.
“We know a lot about air pollution’s effects on human health, and we know a lot about the impacts of air pollution across ecosystems,” explains Tracey Holloway, a professor in UW-Madison’s Nelson Institute for Environmental Studies. “We were surprised to discover how little we know about how air pollution affects birds.”
Writing Aug. 11 in the journal Environmental Research Letters, Holloway, an expert on air quality, and her former graduate student Olivia Sanderfoot, sort through nearly 70 years of the scientific literature to assess the state of knowledge of how air pollution directly affects the health, well-being, reproductive success and diversity of birds. This work is part of Sanderfoot’s ongoing National Science Foundation Graduate Research Fellowship.
According to the Wisconsin team’s survey of the literature, only two field studies since 1950 have looked at any aspect of the health and ecological well-being of wild bird populations in the United States. Globally, there are only a handful of studies that assess the impact of direct exposure to air pollutants on bird health. Those encompass studies of just a few dozen bird species of the roughly 10,000 or so species of birds known worldwide.
Part of the problem, says Sanderfoot, are the many variables in play. Not only are studies of wild bird communities difficult to implement, but factors such as types and levels of air pollution, dynamic atmospheric conditions, species-specific responses, and the difficulty of teasing out direct versus indirect effects of air pollution can confound even the most basic efforts to assess how birds fare when exposed to chemicals in the air.
“There is a lot of work to be done in this area,” says Sanderfoot. “Air quality is an ever-changing problem across the globe. There’s a need to look at different types of air pollution and different species all over the world. We have a huge lack of understanding of the levels of pollution birds are exposed to.”
Gaps in our understanding, according to the new study, include air pollution’s effects on the avian respiratory system; toxic effects on birds, including elevated stress levels and immunosuppression; behavioral changes; and effects on reproductive success and demographics, such as changes in population density, species diversity and community composition.
Holloway, who leads the NASA Health and Air Quality Applied Sciences Team (a multi-institutional team of researchers that serves as a nexus for analyzing…