With an old computer and 30 dollars worth of off-the-shelf components, you can gear up with cutting edge avian monitoring technology and help save the birds.

For years, birdwatchers counted by sight during the daytime. The night — when most migratory birds travel — was literally hidden to them. But that's changing. Anyone can attach a microphone to a computer running birdcall-identifying software and track birds passing overhead in the darkness.

"You wouldn't be able to understand what's happening at night without this technology," said Andrew Farnsworth, a Cornell University ornithologist. "And when it comes to recording the things I work on, that's something anyone can do."

Scientists already depend on citizen birdwatchers for data that provides the foundation for estimates of species health and behavior. Their spare-time jottings are collated in efforts like the Great Backyard Bird Count, eBird, North American Bird Phenology Program and Project Feederwatch. With hundreds of species threatened by habitat loss, climate change and pollution, that data is now invaluable for conservation efforts.

But because many species migrate at night and are hard to find during the daytime, birders can miss them, said Farnsworth, or are forced to use proxy measures: If a bird seen yesterday isn't seen today, then it probably left. "It's not that the proxy methods are bad," he said, "but we're finding this method of nocturnal tracking can be incredibly powerful."



For the last decade, Farnsworth has recorded the special calls used by migratory birds to coordinate their nocturnal flights, painstakingly matching sounds plucked from the night to individual species and then refining population-research methodologies by comparing his records to daytime observations.

Farnsworth uses high-tech microphones, but he learned his craft from William Evans, a former Cornell University ornithologist who developed the initial recording setup and pared it down for the DIY crowd.

"It's one resistor, two capacitors, a 9-volt battery, a microphone element, a dinner plate, some Saran wrap and a flower pot," Evans said.

"It costs less than thirty bucks, and you can build it in a couple hours. You can potentially monitor thousands of birds in a night. And that's something we've never been able to do in the field."

Farnsworth and his colleagues have accumulated about 30,000 hours of nighttime recordings from microphone-and-hard-drive setups deployed across the central and eastern United States. Using software to extract bird calls from dead space, those recordings can be compressed to a length of several days. A researcher can compile records of a whole migratory season from dozens of locations in less than a week. "You've gained a tremendous amount of information, much more efficiently," said Farnsworth.



Instructions for your own bird-recording setup can be found at Evans' website. The microphone connects to a computer running standard audio recording software, and can be put on a roof or out a window.

Because the microphone is tuned specifically to the high frequencies used for migratory bird calls — which are much higher than frequencies used in mate-attracting or territory-marking birdsong — traffic and airplane noise doesn't register. A single hard drive can hold a season's recordings.

Software to compress the recordings and identify individual species can also be downloaded from Evans' site. These are, for the moment,

Windows-only, but programmers who can help port them to other operating systems are welcome, and can obtain the source code from Evans.

Bird identification software is still relatively rudimentary, tagging roughly a dozen species, compared to the hundreds that can be identified by trained listeners. Other species are being added as quickly as they can be linked to flight calls, said Farnsworth, but for now DIY bird monitors should send their recordings to the Cornell laboratory.

"We can turn one expert observer into a hundred, or a thousand, by deploying these microphones and getting information back to a group of people who know how to identify the tough things and summarize it," he said.

In the next several years, Farnsworth hopes to partner with conservation organizations to establish online communities where avian audiophiles can upload their recordings, producing databases like those already established by citizen birdwatchers. Audio recordings will supplement visual observations, allowing researchers to generate ever-more-clear pictures of species health and migratory patterns that have yet to be understood.

"You go 20 miles in one direction, 20 in another, and you have a different pattern," said Evans. "These are very complex routes that vary from year to year at different sites. And over the next 100 years, once we have the reference data sets out there, people will be able to monitor from their homes and start filling in the gaps."

Even if every species can't yet be identified with software, birders can still take pleasure from connecting with an avian world otherwise hidden to their eyes and ears.

"You can get information about birds flying from Canada to South

America from your house, from a window in New York City," said Evans.

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