Nocturnal flight call (NFC) recording offers a different mode of birding that helps monitor species and numbers migrating through an area (Common Nighthawk photo by Paul Konrad).

A new mode of birding gained some momentum during the recent spring migration, with a growing number of birders using do-it-yourself recording setups and free software to listen in and record birds calling as they migrate high overhead – at night. Each spring and fall, millions of migratory birds fly by night between their southern wintering ranges and their northern nesting areas, and back. Birders are helping researchers who are making significant strides to better understand this biannual phenomenon, because night migration remains steeped in mystery because nocturnal migrants are difficult to count and identify.

Fortunately, the birds themselves offer a clue: They make species-specific flight calls that scientists and birders have learned to record, identify, and count. Once limited to biologists and only the most hardcore members of the birding community, now a new wave of birders is tuning in to these calls, using DIY recording equipment to experience what some cheekily call “the dark side of birding.”

Nocturnal flight call (NFC) recording offers a different kind of birding. It doesn’t require binoculars or even stepping foot outside. Instead, a microphone placed on a roof or wedged into an apartment window allows birders to eavesdrop on migrating birds flying overhead. On calm quiet nights, inexpensive microphones are able to record birds calling hundreds of feet in the sky, far beyond the reach of our hearing, and cache their calls on a recording device for later review and identification.

Across the globe, birding’s popularity surged during the covid pandemic, and for many birders NFC recording offered an innovative means of birding while remaining safe at home. In the United Kingdom, where NFC recording is known as “Nocmig,” Mark Pearson began recording nocturnal migrants just as the pandemic, and spring migration, were beginning to peak. Pearson, a lifelong birder, writer, and nature guide, has watched the trend ignite throughout the UK during the past year. “Nocmig has gone absolutely through the roof, from a niche of birding to wonderfully popular and populist, and anybody can do it,” says Pearson, who has recorded birds that he rarely or never sees while birding during the day. “Almost anything can fly over. It’s magic.”

While some NFC enthusiasts like to listen live on peak migration nights, most record the action while they sleep. Nocturnal flight calls are typically less than a second long and notoriously challenging to identify by ear, so recording them for later review makes the ID process easier. After a night of recording, birders use free computer software, such as Audacity, to transform the night’s bird activity into a spectrogram, and that’s when the excitement really starts.

For newcomers to this new aspect of birding, using inexpensive recording devices and a growing set of resources are making it more accessible than ever. A Facebook group has become a hub for the growing NFC community in the United States. It’s helpful in many ways, such as f you are uncertain about an identification? Upload your recording and it’s sure to spark a conversation between experts and beginners alike.

Corey Husic, a Los Angeles-based NFC enthusiast and the group’s founder, says Facebook is a perfect place for the community to gather. Most early discussions were reports from people listening; now you will find discussions about programming and software as some people turn toward automation for recording, detection, and identification, Husic wrote in an email, adding that the group has doubled membership to more than 2,000 since the pandemic began.

While NFC recording is a way for many birders to step up their birding and boost yard lists, their observations are also feeding important community science databases. The Cornell Lab of Ornithology’s eBird, the largest community birding platform, now has a protocol for sharing NFC checklists. Benjamin Van Doren, a postdoctoral associate at Cornell, noted that the number of NFC checklists submitted in the United States doubled during the first year of the pandemic, with no sign of slowing down in 2021. “I think we’re at the cusp of being able to spread nocturnal recording and monitoring of bird migration really far and wide, and start to use it for real, meaningful monitoring,” Van Doren explained.

In what has been called “a golden age of observation,” biologists have been employing a host of technologies to unravel the mysteries of nocturnal migration in recent decades. Radar tech has emerged as an especially powerful tool to study the timing and magnitude of how birds fly by night, but with one big caveat - it can’t identify species.

In that way, NFC recording is unique, helping prove that Pine Siskins call and migrate at night, for example, and offering a deeper look into species-specific migratory behavior. More so than tracking devices and radar, NFC birding also runs the gamut in terms of technological sophistication, from listening to calls by ear and using simple recording devices like a smartphone to more complex recording setups and automatic call-detecting software.

Bill Evans remembers a time when few nocturnal recordings existed. After a life-changing experience listening to a massive night flight as a college student in 1984, Evans dedicated his life to studying nocturnal calls and making NFC accessible to others. In 2002, he completed the first-ever NFC field guide with Michael O’Brien, a foundational resource for learning vocalizations. “You don’t have to go to Costa Rica, you don’t have to go to Alaska for birding; you can tune in to a lot of these species as they fly right over your house,” Evans said.

Being part of the bustling NFC birding community, where experienced recordists eagerly welcome and help newcomers, is its own reward. “That’s where the fun is,” Evans says. “Whatever age someone gets involved.”

To refer to the original Audubon article, see https://www.audubon.org/news/how-birders-are-boosting-their-yard-lists-while-they-sleep