he yellow Townsend Warbler lay lifeless on the gravel ground near Grant county, New Mexico, the eyes in its yellow-striped head closed, its black feathery underbelly exposed. Just days before, the migrating bird – weighing 10 grams, or the equivalent of two nickels – might have been as far north as Alaska. But it met an untimely demise in the American south-west, with thousands of miles still to go before reaching Central America, its destination for the winter. The warbler is one of hundreds of thousands of birds that have recently turned up disoriented or dead across the region, where ornithologists have described birds “falling from the sky”. The mass die-off has been tentatively attributed to the historic wildfires across California, Oregon and Washington in recent months, which may have forced birds to rush their migration. But scientists do not know for sure – in part because nobody knows precisely how wildfire smoke affects birds. A photo of the dead warbler was uploaded to iNaturalist, a crowd-sourced app used to identify plants and animals, as part of the Southwest Avian Mortality Project, a collaboration between New Mexico State University and others that invited users to crowd-source information about the die-off. The project has now logged more than 1,000 observed dead birds, encompassing 194 species – data that is being shared with the researchers to better understand what led to such a major mortality event. “For really solid science, it is good to have long-term data trends,” said Allison Salas, a researcher who helped establish the project. “But with increasing changes to climate and rising temperatures, we do not have enough time to collect the data – things are changing faster than we can keep up with.” This sort of platform, and the citizen birdwatchers who populate them, have become a critical tool for scientists trying to unravel the mysteries at the intersection of birds, wildfires and climate change. “There are many more citizen scientists distributed in diverse arrays than there are professional scientists or wildlife rehabilitators,” said Andrew Farnsworth, a senior research associate at Cornell Lab of Ornithology, the institute that runs eBird, a popular app for logging bird sightings. “The power of eyes in many places is huge.” A physiological mystery Rodney Siegel is the executive director of the Institute for Bird Populations, a non-profit group that works with professional scientists and amateur naturalists to monitor bird populations for conservation. He said that while scientists believe that birds, like humans and other animals, are susceptible to the effects of smoke, “there is still a lot we don’t know”. “We don’t have a ton of information on the immediate, direct effects of smoke and wildfire on individuals,” he said. It may seem unbelievable that this question about one of the most ancient creatures on Earth remains unanswered, but there are several good reasons, Siegel said. For one, it is difficult to properly survey the before and after effects of fire when we rarely know in advance where the next wildfire will emerge. And, of course, because birds can fly, they are not trapped in smoke-filled areas as often as other species. “It probably hasn’t been addressed a whole lot by scientists yet because, unlike a lot of other wildlife, birds can escape fire and smoke relatively readily,” Siegel said. But the ability to escape is diminishing. In the case of the recent fires on the west coast, there were few places birds could have traveled without smoke. Hazardous air quality choked the majority of the west for weeks, with smoke rising thousands of feet into the atmosphere, turning the skies orange. In early September, the growing plume from historic wildfires could be seen from space and eventually made its way to the skies over the east coast. “These enormous smoke plumes are harder to escape than those from smaller fires that have been more typical for the last century,” Siegel said. “This is a really unusual phenomenon without a lot of precedent – and it is unknown how that might affect birds.” It’s important to note that not all fire is bad for birds, he added. California is home to more than 400 species of birds, making it one of the country’s most diverse states in terms of wildlife. Many ecological systems and the birds that inhabit them thrive in the aftermath of small fires. Some like the lazuli bunting, known as a “fire-following” species, have even evolved to thrive in the aftermath of fire events. This bolsters the theory that smaller, less severe fires could be good for wildlife long-term. Some theories A leading theory behind the south-west die-off is that widespread smoke pollution may have forced birds to start migration sooner than expected, said Roger J Lederer, who taught ornithology and ecology at the California State University, Chico, and has written several books about birds and their behavior. “Most of the birds we saw dying were migratory; migration had just started and they were trying to flee the smoke-filled areas but couldn’t find any food,” he said. “It wasn’t the physiological effects of smoke necessarily, they just starved to death.” Beyond the effects of smoke on migration patterns, the rise of megafires is also drawing unprecedented attention to the effects smoke may have on a bird’s delicate breathing. Birds and their lungs are certainly affected by smoke, Lederer said, even if we don’t know exactly how. Most of us have heard the phrase “canary in a coalmine”, which comes from the fact that birds are particularly sensitive to toxins in the air. Lederer has also heard many reports of pet birds dying due to different kinds of fumes in the home. The sensitivity could have something to do with birds’ unique respiratory system. While humans and other mammals use their diaphragm to inhale oxygen and exhale carbon dioxide, birds possess a far more efficient system, essentially inhaling and exhaling at the same time. This allows them to get enough oxygen to fuel near-constant activity and to breathe at much higher altitudes than mammals. To do this, birds have tube-like structures called parabronchi, similar to human alveoli in the lungs, which are covered with sacs and capillaries for gas exchange. And as in humans, smoke damage can burst those bubbles, creating less surface area to exchange oxygen and making it more difficult to breathe. “This is unprecedented – there have been fires for years and years but this is the first year everyone is paying attention to the impact on birds,” Lederer said. Community scientists fill in the gaps As scientists at New Mexico State University began to recognize the size and scale of the mass bird die off this year, they invited members of the public to log bird deaths on iNaturalist. The format is collaborative: one person can upload a photo of a flower or animal, and more experienced naturalists can comment to confirm what it is. The data is all geotagged when uploaded, giving scientists details about locations. “There are limitations in science – we can’t be in every place all the time,” Salas said. “Being able to incorporate a standardized way of collecting data from everybody across the country or the world is extremely helpful.” Researchers are increasingly relying on data collected by citizen scientists and birdwatchers to better understand the effects of climate change, including intensifying wildfires, on bird populations, Salas said. “Citizen science or community projects are great because they are real time, they are happening in the moment, and it allows us to kind of keep up with everything that’s going on and still be able to document it over time,” she said. One of the most popular tools for the average birder is eBird, an app created by the Cornell Lab of Ornithology alongside the National Audubon society, to crowdsource data on the locations and numbers of bird populations globally. In recent years it has recorded as many as 100m bird observations per year. Citizen data is “invaluable” for tracking where, when, what, and how many birds are present in a particular area, said Andrew Farnsworth, who works there. “Leveraging many sources of information is critical.” Birding is particularly amenable to new and amateur naturalists, said Lederer. Crowdsourced data from people of all skill levels is helpful to scientists who “just don’t have enough manpower”, he said, especially as climate change and its effects become more widespread. “People are paying attention now more than ever, which is a good thing. Until we know what is happening, I’m not sure we can do anything about it.”