There was a recent report (August 2020) of hundreds of thousands of birds found dead in New Mexico. Biologists figure it has something to do with the wildfires that are plaguing the western states. Dead birds are also being found in Colorado, Texas, and Mexico. Many of them were migratory insectivorous birds. Live birds were seen picking insects off the ground when they usually feed in the air. Even swallows that can’t walk on the ground were feeding there.
Apparently some birds were driven by the fires to migrate early or at least leave their breeding grounds to escape the flames. Others changed their migratory routes, perhaps taking pathways that offer little food. The extreme heat in some areas added to the mortality. Then there was an extreme temperature plunge in Colorado one evening, dropping from the 80s to freezing and snowfall overnight.
Biologists are collecting data now to see if they can determine the cause of these mass deaths, perhaps numbering in the millions of birds, but smoke seems to be a major factor.
Birds are probably more sensitive to smoke inhalation than humans because they have a more efficient respiratory system. See my brief lecture on respiration. They are certainly more sensitive to gases such as carbon monoxide and methane which is why canaries used to be installed in coal mines as warning instruments. And we know from veterinarians that pet birds kept in houses can be killed by fumes associated with cooking. Over-heated cooking oil will produce smoke that will cause a bird to gasp and choke. Teflon-coated saucepans, if over-heated or allowed to burn dry, will release toxic fumes that will kill a bird in minutes.
There is a lot known about the effects of smoke and other pollutants on caged and pet birds, but a search of the scientific literature tells me that there has been very little research done on the effects of smoke on wild birds. There is a lot of research on the effects of wildfires on bird populations and their recovery but not what happens to birds during a fire.
Resident birds have to leave the areas which are familiar to them and migratory birds have to change their routes to avoid fires. But can they actually avoid the effects? Rising up to 14 miles in the air, smoke from the U.S. west coast has reached as far as New York and Washington D.C. on the east coast. Fires in Siberia have sent smoke to Alaska.
Wildfires release tiny lightweight particles of soot termed particulate matter or PM, especially large quantities of fine particulates called PM2.5, particles 2.5 micrometers in diameter. (The average human hair is 70 micrometers in diameter, 30 times as wide.) PM2.5 particles can penetrate lung membranes and pass into the bloodstream. These smoke particles also undergo chemical changes that convert them into highly reactive compounds with deleterious effects on cells and tissues.
Satellite monitoring and modeling have determined that smoke from the 2017 Pacific Northwest fires remained in the stratosphere for 8 months. We don’t know much about the effects of smoke on birds but it appears we will have plenty of reasons and opportunities to study it in the near future.
Meanwhile, many genuine thanks to all the firefighters and other first responders who are risking their lives to protect us and our wildlife.