Depressed nestling growth during exposure to smoke from distant wildfires.

Human and animal populations increasingly encounter smoke pollution as climate change enhances the frequency and intensity of wildfires. Most work on smoke effects in animals has studied populations close to fires, populations experiencing small, prescribed burns, or animals in the lab. In June of 2023, smoke from distant Canadian wildfires quickly elevated particulate matter (PM) pollution in a wild house wren (Troglodytes aedon) population for three days before returning to baseline levels. Compared to previous years, nestlings experiencing three days of elevated PM within the first 6 days of life weighed less on days 6 and 10 after hatching and had shorter tarsometatarsus bones, a sign of smaller skeletal size. In contrast, nestlings that hatched before or after this event did not differ in size from previous years. Although sublethal, these effects may have important consequences for survival and reproduction. As wildfire activity increases, more wildlife populations are at risk of smoke-related fitness consequences, even those distant from the blaze.