Oops, I Did It Again

Yes, I cheated again. We published a second post on the Cornell Lab of Ornithology's "Round Robin" blog. This one, titled "How to See a Sound That’s a Half-Second Long," gets into flight-calls a bit more and talks about using spectrograms to "see" sound.

Find out more about this image, including what it sounds like, at Round Robin.

If you missed it, the first post, "Let's Go Biding! . . . At Night . . . Blindfolded," serves as an introduction.

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Stepping Out

Dear Feather and the Flower,

You'll probably find out about it elsewhere on the Internets, so let me come clean. The rumors are true. I've been writing with someone else.

It's only platonic, I swear - please know you are still my one and only blog. But I was approached by another blog, we innocently chatted about our shared interest in birds. We hit it off, the attraction was too great to resist; one thing lead to another, and as of today I've published on a different site.

I don't mean to hurt you, but the other blog means a lot to me. And given a chance, I think you would really get along - Round Robin is popular, attractive, intellectually-stimulating, and funny - what's not too like? Give it a try, see what was posted, I think you'll be excited.

Affectionately,
noflickster

ps I know you want the details, so here they are. Our nocturnal flight-call group wrote a piece about nocturnal migration for the Cornell Lab of Ornithology's blog. We are planning to contribute more throughout spring migration, we expect topics will range from when and where to listen, their importance in conservation and other fields, and several tutorials to introduce species so you can explore this frontier of bird watching. Please let me know (on this site) or the Lab know (on Round Robin) about your experiences in listening for nocturnal migrants, if you find the posts useful, and so on - we are looking for feedback! And if you blog, please consider promoting the posts to your readers: we'd like to reach a wide audience and hear comments about experiences across North America.

Now, I'm stepping out to see some birds - so I have something to post here before I get in dutch with my own blog . . . .

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Flight Call Identification: Veery

This is the first in a series of posts presenting flight calls of nocturnal migrant birds. If you haven't yet, you might want to refer to my introduction to flight calls before, or after, reading this account.

The Veery (Catharus fuscescens) spends its summer in damp, deciduous forests, stretching in a loose band across North America. The song is familiar, often used as an example of the dual syrinx, its downward-spiraling flute-like notes a marvel of nature. Because winters are spent in central and southern Brazil their migration should cover the eastern two-thirds of the U.S., though eBird shows show reports are spotty across the Great Plains. Perhaps this is more likely a testament to the number of observers and the number of Veeries seen during migration. Flight call monitoring might provide a more accurate assessment of where the birds are migrating.

Veery reports according to eBird (map created 28 Aug 2008).
How many of the blank areas are simply "fly over" regions?

Edited to clarify the map: The above map displays all reports throughout the year, both on the breeding areas and on migration. For example, the light green wash (indicating relatively fewer sightings) across the gulf-coast states are migratory observations, the dark green wash across the southern provinces and northern U.S. are sightings from the breeding ground. Dark green indicates high frequency of reports, likely due to repeated observations on breeding territories. Light green, or areas of infrequent observations, are due to the passing nature of the Veery in these areas.

For life history information about the Veery, including listening and viewing the song, visit the All About Birds web site.

Timing-wise the best time to listen in the northern U.S. is now. According the the Birds of North America Online peak migration in New York runs from late August to early September, in Minnesota 31 August is an average peak date. Southern birders have a couple weeks: in Louisiana migration peaks between 15 - 30 September.

Like the other Catharus thrushes, Veery flight calls are relatively low in frequency (pitch) and are relatively long. The call I'm highlighting here, freely available online through the Macaulay Library online archives, is about a quarter-second long (250 milliseconds). I find the thrushes a bit easier to hone in on than the even-quicker warbler and sparrow flight calls.

The Y-axis shows frequency in kiloHertz (kHz), which you can think of this way: the higher the kHz, the higher the pitch of the sound. Johnny Cash sang at low frequencies, Tiny Tim at high frequencies. Annoyingly high frequencies.

Looking at this call we see the Veery's flight call is relatively linear, typically keeping within 2.5 - 2.0 kHz. The frequency usually declines during the length of the call, which is why the pitch falls when you hear it though the heavily-modulated ending may slightly rise. This call shows up very dark and bold, indicating it's pretty loud. The bird must have been close to the microphone when recorded.

Veery flight-call, full speed.

Pretty fast, right? It's intimidating to think this is one of the longer flight calls. Examining the spectrogram shows this call starts pure, the note is slightly-descending but the line is flat, not wavering (modulated). The end of the call is heavily modulated, though, rising and falling very quickly, which gives a distinct "burry" sound.

Listen to the same call at quarter speed, it's easier to hear those characteristics: descending in pitch but unwavering, then fluttering rapidly through the modulated end of the call.

Veery flight-call, quarter speed. Listen to the
descent in pitch, then the fluttery, modulated ending.

Try listening to the quarter-speed version a few times, and once you clearly hear the characteristics try listening to the following clip, the same call at half speed. Can you still hear the characteristics?

Veery flight-call, half speed.

Again, listen to the half-speed version a few times, and once you're comfortably hearing the characteristics at this speed, scroll back up and listen to the full-speed version.

Of course, this is one call of a single individual, and I've mentioned you're bound to encounter variation. That's especially true in Veeries. Oftentimes the Veery's entire call is modulated, though the heaviest modulation tends to be towards the end of the call, like this one. This call could be confused with the other thrushes (Hermit, Wood, Swainson's, Gray-cheeked, Bicknell's; even bluebirds and robins) as well as other species that give thrush-like calls, meaning relatively long and in the lower frequencies. These include tanagers, meadowlarks, and orioles.

For more Veery recordings and spectrograms visit Call Notes & Flight Calls.

• Veery flight call recorded by Bill Evans, 24 April 1990 in Alabama, U.S.
• Recording courtesy of Macaulay Library, Cornell Lab of Ornithology.
• Spectrogram created in Raven Pro, Bioacoustics Research Program, Cornell Lab of Ornithology.
• For more information about the Veery visit All About Birds.

Listening for Flight Calls

In a recent post I highlighted that nocturnal river of birds that flows overhead through the migration months, specifically mentioning we had a big push of Veery through the Finger Lakes region (NY) that week. I realized I hinted around, but never directly said, "Go out and listen!" Let me say it here: on a good night it is truly mind-numbing to realize how many birds are flying over your head in the cover of darkness if not the sheer diversity. As one birder put it, you're likely to hear more Gray-cheeked Thrushes during a couple of hours on a good night of migration than you will ever see in your lifetime.

I also realized some might want to listen for flight calls in their area and try to identify what they're hearing, but wouldn't know what to listen for. Far be it from me to point out something cool but not provide the tools to enjoy it, so I plan to post brief tutorials about some of the nocturnal migrants that you may hear winging their way south. I'll try to time each species profile with their chief migration windows, but as migration peaks will differ with latitude that won't always be possible. You can't please everyone, but there it is.

Updated to add: Jump ahead and learn about Veery calls, or continue reading below to learn about flight calls in general.

So, about flight calls. They're different than the songs used for advertising for a mate or declaring a territory, they're different than the contact notes you'll hear between a mated pair or between parents and offspring, different than the alarm calls. Their function isn't truly known, though current thinking is that flight calls maintain groups and also stimulate "migratory restlessness" (zugunruhe, the "urge to migrate"). If you are interested in a more detailed overview about flight calls I recommend that you read this article.

Flight calls are short. Really, really short. The longest are about a half second long, or 500 milliseconds, and the shortest clock in at about 30 milliseconds. The first time you listen for them it's tough to even hear them, but with some time to acclimate your ears and with some focused listening they'll start to pop out from the ambient noise.

Not only will you hear them, but with enough time, practice, and patience you can hear the characteristics of each call. The calls may be high- or low-frequency (high or low pitch), they can rise or descend in pitch, or they can do both in the same call. They can be heavily modulated, meaning the note wavers and sounds "burry," or be a pure, sweet sounding note. Above all, though, they're short.

Because of their brevity I find the most useful way to learn a call is to study its spectrogram. This has the advantage of seeing the characteristics, a bit easier to process - much like learning what the bird looks like tends to be easier than learning the songs. I then play the recording, but slow it down so I can listen to it at one-quarter of the actual speed. This gives more time to get a handle on the sound, really hearing each characteristic. I then listen at half speed a few times, then finally at full speed. At that point I'm hopefully still hearing the characteristics.

Each species has a unique call, so flight calls can be a useful way to identify nocturnal migrants. Be warned that the experts are the first to admit that not every call can be identified to species, especially by ear. Even with sophisticated analytical software taking dozens of measurements on the spectrograms we often leave calls categorized as a suite of possible species. For example, the Flight Call Library on Bill Evans's OldBird web site includes examples of character groups: calls of various species that are so similar they are near impossible to separate.

There is variation in the calls. It's amazing to me a half second provides enough time to introduce variation, but it happens. Be prepared to let some calls go, lumping them into a loose category ("That sounded like a double-up," or "that was one of the zeep complex") but hopefully many calls will become recognizable.

And even if you don't identify any calls, it's simply a marvel of nature to hear the numbers and the diversity that you may have never realized pass you by each spring and fall.

Finally, a disclaimer: I'm not an expert in flight call identification. Much of what I've done with them relates to collecting flight calls, meaning I've deployed autonomous recording units and then run detection software to pull out the flight calls. I've spent hours browsing those detections to separate the calls from the "false-positives" (or, more accurately from where I sit, the "junk"). In researching and writing this series of posts I'm hoping not only to educate anyone not familiar with flight calls, but I'm also anticipating the process will allow me to dig deeper into the subtleties of each species' call. Naturally, I hope you will jump in and join a dialogue about what I present here and especially what you're noticing at your location.

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Cascading River of Birds

If you've paid attention to bird reports recently you already know migration is well underway, and has been, conservatively, for about six weeks. Was it Pete Dunne who once pointed out that if summer were bookended by bird migration it would only be a few days long? Whomever it was went on to point out the last migrant passerine was spotted winging its way north a couple of days before the summer solstice, and a couple of days after the solstice the first yellowlegs was on its way south.

Here in the Finger Lakes region of New York shorebird reports have been steady from Cayuga Lake and Montezuma NWR, and we've already had a Solitary Sandpiper show up at our backyard pond in the southern tier. In fact, it was a year bird and the first we've recorded on fall migration. More my speed these days, though, are the sound waves emanating from the river of birds that will be flowing over our heads for the next couple of months.*

If you've never been you should head over to Bill Evans's "oldbird.org" website. Bill's sole intention is to learn about nocturnal bird migration and share the knowledge with anyone who cares to listen. He focuses on flight-calls, those short, simple "tseeps" and chips (among other impossibly short notes) you may hear overhead. Not only does he teach you how to identify the sounds with Flight Calls of Migratory Birds, a CD-ROM developed with Michael O'Brien, but he also provides instructions on how to build your own microphone set up using materials from local garden and grocery stores (after a trip to Radio Shack, naturally). And that's not all, he also provides analysis software free so you can use your computer to view, study, and listen to what flew over your house while you slumbered. No more dark circles as you stumble into work the next morning!

As I mentioned in an earlier post, I also study nocturnal migration, though we use autonomous recording units developed at the Lab. Bill's web site and his CD-ROM have been instrumental for me, learning to identify those less-than-500-millisecond long calls; it's opened a new avenue of birding. In fact, I'm building my own "flower pot" microphone so I can record migration over our house. What a mesh, for me, of "work" and "play," and now that the floodgates are open on this fall's migration I'm excited to listen for what's passing by. Recently we've been hearing more and more activity in what Sinatra called the wee small hours: three nights ago it was a huge push of Veerys with a smaller flight the next night.

More to come on nocturnal migration as the season progresses, and happy fall to everyone!

*Dates may vary with latitude, offer available across North America. Act now, don't miss out!