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Pine Siskins by Bob Vuxinic via Birdshare.

By Pat Leonard

With puzzling variability, vast numbers of birds from Canada’s boreal forests migrate hundreds or thousands of miles south from their usual winter range. These so-called irruptions were first noticed by birdwatchers decades ago, but the driving factors have never been fully explained. Now scientists have pinpointed the climate pattern that likely sets the stage for irruptions—a discovery that could make it possible to predict the events more than a year in advance.

The researchers found that persistent shifts in rainfall and temperature drive boom-and-bust cycles in forest seed production, which in turn drive the mass migrations of Pine Siskins, the most widespread and visible of the irruptive migrants. “It’s a chain reaction from climate to seeds to birds,” says atmospheric scientist Court Strong, an assistant professor at the University of Utah and lead author of the study.

Many seed-eating boreal species are subject to irruptions, including Bohemian WaxwingsCedar Waxwings, Boreal Chickadees, Red Crossbills, White-winged Crossbills, Purple Finches, Pine and Evening Grosbeaks, Red-breasted Nuthatches, and Common and Hoary Redpolls. The authors focused on the Pine Siskin, a species featured prominently in earlier work on irruptive migrations.

Previous studies have found evidence that irruptions are triggered by food shortages caused by the large-scale collapse of seed production in northern pine, spruce and fir forests.

“We’ve known for a long time that weather was probably important, but prior analyses by ecologists have been unable to identify exactly what role weather was playing in this phenomenon,” says ecologist Walt Koenig, a senior scientist at the Cornell Lab of Ornithology and coauthor of the new study incorporating climate science. “It’s a good example of the value of interdisciplinary work,” Koenig says.

To resolve the question, the scientists turned to a remarkable trove of data gathered by backyard birders as part of Project FeederWatch, a citizen-science initiative run by the Cornell Lab of Ornithology. FeederWatch volunteers systematically record bird sightings from November through early April and they gave the scientists more than two million observations of pine siskins since 1989. The crowdsourced data makes it possible to track the movement of bird populations at a continentwide scale.


Many seed-eating boreal species, like this Boreal Chickadee, move elsewhere to find overwintering habitat with adequate food, and are subject to irruptions. Photo by Jess4407 via Birdshare.

“Avid birders across the U.S. and Canada have contributed sustained observations of birds at the same broad geographic scale in which weather and climate have also been observed and understood,” says coauthor Julio Betancourt, a senior scientist with the U.S. Geological Survey in Reston, Virginia.

Pine Siskins breed during summer in Canadian boreal forests, where they rely heavily on tree seeds for food. When seeds are abundant, Pine Siskins in eastern North America largely stay put in the northern coniferous forests of Canada through the winter. But when seed production is poor, Pine Siskins and other boreal birds move elsewhere to find overwintering habitat with adequate food. During these irruptive years, the eastern populations of Pine Siskins forage as far south as the Appalachian Mountains. Western populations show less variability in irruptive movements.

Amateur birdwatchers have recorded dramatic shifts in siskin migrations over the years. The winter ending in 1990, for example, featured a massive “superflight” south of the boreal forest, while during the winter ending in 2004 there was a near absence of boreal Pine Siskins in the U.S. The winter ending in 2009 saw another big irruption south of the boreal forest, followed by greatly reduced counts the following winter.

In the new study, researchers combined FeederWatch observations with climate data in a statistical analysis. This allowed them to link bird population movements with established patterns of climate variability across North America. As expected, they found that extremely cold winters tend to drive birds south during the irruption year.

More surprisingly, the researchers found a teeter-tottering pattern between the north and south that influences bird migrations two to three years later. When the prevailing weather is wet and cold and unfavorable to seed production in one region, it tends to be warmer and drier and favorable to seed production in the other region.

This climate “dipole” tends to push and pull bird migrations across the continent. The heaviness of seed production in a given year depends on how favorable the climate was during the two or three previous years required to set and ripen seeds. That means that, in principle, it might be possible to predict irruptions up to two years in advance.

The finding also raises a question about the impact of global climate change: could the perturbation by massive carbon dioxide emissions disrupt the coupling between north and south such that unfavorable conditions unfold simultaneously, leaving birds with poor seed supplies everywhere in some years?

The answer is unknown. “The boreal forest is the world’s largest terrestrial biome and is home to more than half of North America’s bird species,” says coauthor Benjamin Zuckerberg, an assistant professor of wildlife ecology at the University of Wisconsin-Madison. “It is likely that these irruptions, driven by climate, are a critical indicator of how climate change will affect northern forests and their dependent species.”

For more information:

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By Pat Leonard

***Update: since this was posted, the Global Big Day tally has continued to rise (as people entered the day’s checklists into eBird after the fact). The total stands at 6,069 species as of May 27, 2015, including more than 43,000 checklists and nearly 14,000 participants.***

When the Cornell Lab of Ornithology invited bird watchers everywhere to go birding on May 9 and report their sightings for the first ever Global Big Day, no one knew what to expect. The results have exceeded all expectations! From Panama to Australia, India to Lithuania, participants enthusiastically accepted the invitation, tallying more than half of the world’s bird species. The numbers are still going up as participants continue to enter their lists through May 12.


Black dots indicate where checklists were submitted for Global Big Day. The large yellow dot shows a new checklist dropping in.

See current results.

But the day also turned into something the numbers cannot capture. Global Big Day was defined by team efforts worldwide and was not necessarily about competitive goals or checking off species. It was about truly appreciating birds, unique habitat, and diversity—and about sharing the excitement of birding and the importance of conservation.

Thank you to everyone who donated to support the Lab’s Global Big Day teams. There’s still time to make a gift toward bird conservation—the other driving force behind this event.

Worldwide Overview

As of Monday morning, May 11, Global Big Day included participation from more than 11,000 individuals from 119 countries, tallying more than 5,600 species on more than 36,000 checklists. A few highlights:

  • The very first bird reported for Global Big Day was a Bush Thick-knee from Queensland, Australia
  • Every country in Central America participated, along with 16 countries in the Caribbean. In Panama, Sociedad Audubon de Panamá mobilized teams nationwide, with 84 birders posting over 650 checklists and 620 species, almost two-thirds of the country’s species! Prominent and luxurious birder destinations including the Canopy Family (Canopy Tower, Canopy Lodge, Canopy Camp, and Canopy B&B), Los Quetzales Ecolodge and Spa, and Tranquilo Bay Eco Lodge also mobilized teams to participate in Global Big Day, hosted Cornell Lab staff in the lead up to the Big Day, and provided amazing logistical support. Every one of them provides a great birding destination for visitors to Panama and is highly recommended.
  • South America had stellar participation. The cumulative lists for both Peru and Brazil topped 1,000 species in each country, with Peru slightly ahead of Brazil
  • In Peru, the organization CORBIDI motivated birders across the country; Peru’s list edged out Brazil to become the highest species count for any country in Global Big Day
  • Brazil’s birders also compiled a 4-digit species list, thanks to a big mobilization effort from SAVE Brasil and Butantan Bird Observatory
  • More than 28,500 checklists were submitted from all 50 U.S. states and every Canadian province and territory
  • 30 countries in Europe joined the effort; kudos to Lithuania, where the organization ORNI prompted participation and resulted in 22 checklists
  • India is one of the most active eBird countries year-round and turned in a most impressive 548 checklists during Global Big Day
  • Taiwan contributed an exceptional number of sightings, reporting more than 200 species
  • In Malaysia, thanks to the Sandakan Borneo Bird Club in the Sabah portion of Borneo, participants submitted 53 checklists with a whopping 333 species
  • BirdLife Zimbabwe did a great job with the event and birders there have contributed 232 species, one of the highest totals from a country in Africa so far.
  • Australia is in the top 5 participating countries and closing in on an astonishing 500 species

Sapsuckers in Panama


Team Sapsucker in Panama (L-R) Carlos Bethancourt, Chris Wood, Jessie Barry, Tim Lenz, Marshall Iliff. Photo by Carlos Gómez.

“On Global Big Day, we were Panamanians,” says Chris Wood, captain of the Cornell Lab’s Team Sapsucker and co-leader of eBird. He and four others on the team reported 320 species during the day, reveling in an exceptionally warm welcome from a country that may be small geographically but is super-sized when it comes to diversity of species and its importance to birds throughout the Western Hemisphere.

“This event is promoting interest in and appreciation of birds,” says Wood. “Once you have that, you have a solid foundation for long-term monitoring. Monitoring results in better understanding about where birds go and how they use the habitat—and it helps create more effective conservation efforts.”

For the Sapsuckers, birding in Panama was an eye-opening experience. Their day began at midnight at home base, the Canopy Tower Lodge. The first bird they heard was a Mottled Owl followed by a Great Tinamou and a Black-and-white Owl. Pre-dawn birding included one of several life-birds for the team, a Rufous Nightjar, along with Capped Heron and Boat-billed Heron.

Daylight brought humidity and temperatures in the nineties. The team spent 2 hours on the famously birdy Pipeline Road, which is really a dirt track through the forest. They bounced along in the so-called “BirdMobile” supplied by their Canopy Tower hosts and driven by Domi Alveo. Having Canopy’s Tower’s Carlos Bethancourt on the team was another eye-opening experience, notes Sapsucker Marshall Iliff. “Carlos’s knowledge of Panamanian species and his ability to find them and recognize their sounds is extraordinary,” says Marshall. “We felt truly humbled!” For example, Panama boasts about 100 species of flycatchers alone, each with slightly different whistles and trills. The Sapsuckers counted 39 of them.


Following the Pipeline Road. Photo by Carlos Gómez.

The entire day was punctuated by memorable moments as the team moved from tropical rainforest to marshes, highlands, and rice fields. Imagine having a Spectacled Owl fly by so closely you can feel the wind from its wings; having a Pheasant Cuckoo perch at eye level along the Pipeline Road; floating down the Chagres River to discover 40 super-rare Masked Ducks; hearing the spine-tingling “roar” of a Rufescent Tiger-Heron at night while Panamanian night-monkeys cavort in the trees. For Sapsucker Tim Lenz, the highlight was seeing dozens of hummingbirds jockeying for position at backyard feeders in the Cerro Azul development northeast of Panama City, including male Rufous-crested Coquettes with their punk-rocker hairdos.

After being dazzled by so many new species the Sapsuckers say they finally “felt like competent birders” again when scoping the bay at Panama City where a large proportion of the global population of Western Sandpipers winters, along with other familiar Arctoc breeders such as Black-bellied Plovers, Whimbrel, and Short-billed Dowitchers.

The Sapsuckers ended the day at rice fields and lowland marshes where they identified the Pied Water-Tyrant and Cocoi Heron, finally wrapping up with Lesser Yellow-headed Vulture, Common Nighthawk, and Barn Owl in the rapidly fading light of a tropical sunset. If the day could be summed up in one word, it might be “diversity.”

“The huge diversity of birds sounding off during the dawn chorus almost overwhelms your senses,” says team member Jessie Barry. “It’s a blend of so many birds, some familiar and others more scarce—there are dozens of species you try to pick out at each stop. It was a dream come true to see so many birds.”

“Inspiration” is another word that keeps coming up. Every step of the way, the Sapsuckers say they were inspired by the efforts of participants around the world and the phenomenal levels of participation in Global Big Day which they could follow in real time on the eBird website.

Redheads in New Jersey


For the state Redheads team and everyone else, finding birds was hampered by thick fog. L-R: Ben Barkley, Luke Seitz, Brendan Fogarty, Benjamin Van Doren. Photo by Andy Johnson.

The Big Day spirit of cooperation was also evident at the 32nd annual World Series of Birding in New Jersey. Teams were allowed to share information for the first time and it served everyone well as they all struggled with persistent fog, a bit of rain, and migrant species that vanished overnight.

Three teams made up of Cornell University students, collectively called Team Redhead, competed in the event’s state, county, and Big Stay divisions, registering stellar performances across the board.

“Even though the conditions were not great—we went an hour without finding any new birds at one point—we still came away feeling really good about the day,” says state Redheads team member Ben Barkley. “Even though it’s still a competition, there was a lot of sharing.”

The state team, made up of Barkley, Andrew Dreelin, Brendan Fogarty, Luke Seitz, and Benjamin Van Doren, totally upended the traditional birding route, starting the day with a Northern Mockingbird in the Meadowlands. But the real highlight was hearing a bird that’s been missing from World Series tallies for years: the secretive Black Rail, a find made possible after another team shared the bird’s location. The state Redheads team defended last year’s championship title, bringing home the Urner Stone Cup for the highest species total: 208. They happily shared the title with a Maryland youth team called the Raucous Gulls. Although technically not eligible for the award, the youth team tallied 216 species.

The Redheads team that birded Cape May County included Teresa Pegan, Eric Gulson, Mary Margaret Ferraro, and Max Witynski. They were very happy with their tally of 148 species which put them in second place in their division.

The Big Stay team, which did its birding in one location, won its division by just one species, reporting 71 in all. Sarah Dzielski, Lauren Flesher, Nathanial Hernandez, and Reid Rumelt made up this team and were thrilled to include a Mississippi Kite in their final tally.

The Swarovski Carbon Footprint award is shared by two teams, one of them the CMBO Birds and Blooms Scarlet Knight Herons which was raising funds for the Cornell Lab with its efforts. The team of David La Puma, Don Freiday, Timothy Freiday, Jessica Gorzo, and Bill Lynch identified 126 species as they did their birding without the use of a motorized vehicle. Way to go!

Fueling the Conservation Engine

For the Cornell Lab of Ornithology, Big Days have traditionally been a means of raising funds to support its programs in education and conservation and to assist with undergraduate research through the Redhead Fund. This year was no different. Thanks to the generosity of supporters we are closing in on $300,000 toward our goal of $500,000 (so please consider donating to help our cause). As participation in Global Big Day grows, the hope is that conservation groups in other countries will find the event a useful way to bring in funds for their important work as well.


“I believe we will look back on this day as a pivotal event,” says Chris Wood. “This is when we really begin engaging a global audience and making Big Days about uniting birders in a collective global effort to survey birds, doing it together, and forging vital partnerships.”


An extraordinary talent: Sapsucker Carlos Bethancourt.

Many thanks to all who have supported Team Sapsucker and Team Redhead this year and who participated in Global Big Day. And an especially heartfelt “thank you” to Raul Arias and the entire Canopy Family for their tremendous hospitality during our team’s visit to Panama.

“There is no question that we would have seen far fewer birds and been much less comfortable without their help on every level,” says Wood. “Their local expertise, excellent lodging, delicious food, smooth logistics, and superlative skill at finding birds are simply unmatched. Everyone in the Canopy Family was simply amazing.”

Thanks to drivers Domi Alveo and Lorenzo Ibarra; to Jenn Sinasac who coordinated the entire visit; to Rosabel Miro and the staff at Panama Audubon; to eBird reviewers Jan Axel and Darien Montañez; and to the incomparable Carlos Bethancourt.

“Carlos was clearly the most valuable member of Team Sapsucker and personifies the rare combination of traits one looks for in the very best leader, conservationist, guide, and friend. Carlos—you will always be a Sapsucker!” says Chris Wood.

The Sapsuckers agree: “We can’t wait for next year!”

For more on the teams, Global Big Day, and more:

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Author Laura Erickson, and wildlife photographer Marie Read talk about their new book, Into the Nest: Intimate Views of the Courting, Parenting, and Family Lives of Familiar Birds, that documents every stage in the family lives of birds. Their book offers rare glimpses into birds’ daily lives during the breeding season; from dramatic courtship to nest construction, egg-laying, and first attempts at flight by the young.

The talk took place on May 4, 2015. It was part of the Cornell Lab’s long-running Monday Night Seminar series, a tradition established decades ago by Lab founder Dr. Arthur Allen. If you enjoyed this seminar, check this page for our list of future speakers—we’ll note which upcoming talks will be livestreamed—or come visit us in person!

See our index of archived livestreamed seminars to enjoy more talks from the Cornell Lab.

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singing Prairie Warbler by Joshua Clark

Prairie Warbler by Joshua Clark via Birdshare.

Guest post by Tom Stephenson and Scott Whittle, authors of The Warbler Guide

Spring is here, and with it come the warblers, with their spectacular colors and beautiful songs. Unfortunately for many birders, however, spring also means the frustration of learning or relearning warbler songs. When it comes to birding with our ears, almost everyone—including us—is at a much lower level than when birding with our eyes. A big part of this problem is there’s never been any consistent system for studying or learning songs.

This spring we encourage you to try again, but this time with a system that can help you describe and remember what you’re hearing. By using a few simple, objective terms, you can understand the structure and quality of a song, and identify what’s unique about it. We’ll describe it here and show how to use it to identify 3 great warbler sounds of spring. (You can also download our guide on how to recognize 8 warbler songs.)

When You Listen to a Song, Ask These 3 Simple Questions

The Warbler Guide system is based on a simple idea: if you can accurately and objectively describe a sound, you can identify it. As a bonus, when you describe a song you pay closer attention to its details, and it becomes easier to recognize.

One reason why birders can identify birds by sight is that we have a whole vocabulary for it: words like “eyeline,” “streaking,” “wingbars,” “upperparts.” But how to describe a song? We might describe it as “sweet” or “rough” or “dark,” but these words mean different things to different people. Or we might focus on the melody, like we would with music. The problem there is that many birds don’t have a consistent melody—try memorizing the constantly changing song of a Northern Mockingbird, for example.

So instead, we’ve developed three simple questions that will separate most warbler songs, and many other bird songs: sound quality, pitch trend, and number of sections. Describe these aspects of the song, and then turn to either the Warbler Guide book or Warbler Guide app to quickly narrow down your choices. (Note: For more, see How to Listen to Warbler Songs, in The Warbler Guide. The Warbler Guide app is currently iOS only; an Android version is planned.)

Question 1: What is the Sound Quality of the Song?

We use a few simple terms to describe sound quality in a song: Buzzy, Clear, and Trilled. To help us visualize sounds, we use a very useful tool called a spectrogram. These show you time from left to right and pitch from low to high (more about how to read spectrograms).

the three main sound quality types in bird songBuzzy   Like a bee – a good example would be Black-throated Blue Warbler song.

Clear Something you could whistle. Cardinals have a Clear song, as do Yellow Warblers.

Trilled A lot of sounds in a row that are too fast to count (technically, more than 11 sounds per second). Screech-owls sing a trill, which some birders imitate when pishing for birds. Worm-eating Warbler song is also a trill.

One small twist: sometimes a bird can sing more than one quality in a song. For example, a series of Clear elements followed by a Buzz: we’d call that Partly Buzzy.


Question 2: What Is the Pitch Trend of the Song?

the four patterns of pitch profile in bird song

Click for our guide on how to read spectrograms.

Is the overall pitch of the song Rising, Falling, Steady, or does it move up and down (Variable)? Note that here we’re looking for the overall trend of the song, so if there’s a slight fall in pitch but otherwise the song is mostly rising, then it would still be considered a Rising song.


bird songs with one, two, and three sections

Click for our guide on how to read spectrograms.

Question 3: How Many Sections Does the Song Have?

We break songs down into parts called Sections. A Section begins whenever there is a dramatic change in pitch or speed. Counting the number of Sections in a song can be one of the most effective ways to identify it.

Here are a few spectrograms that show a one-, two- and three-Section song. The gray bars at the bottom of each spectrogram show you where sections start and stop.

In addition to Sections, we can also talk about Elements (the single sounds in song) and Phrases, which are groups of repeated Elements—more on that later.

That’s it! With those three questions, you can describe and separate most warbler songs. Now let’s try some examples.

Try It With a Few Songs

Song #1: Prairie Warbler

Listen to the song and compare it to the spectrogram:

prairie warbler spectrogram

What Is the Sound Quality? This bird has a Buzzy song, which we hear when playing it. We can also see it in the spectrogram: each Element is “fuzzy,” as opposed to straight line, and that indicates a buzz.


A buzzy, rising, 1-section song means Prairie Warbler. Photo by Scott Whittle.

What Is the Pitch Trend? The overall pitch of the song is Rising, with a gradual step up in pitch between each Element.

How Many Sections Are There? We can see in the spectrogram that this bird has a 1-Section song. Don’t be fooled by the gradual rise in pitch: although the pitch is changing a little between each Element, it’s a steady change, and there is no sudden change in pitch or speed, so that makes it a single Section.

So we have a song that is Buzzy, Rising, 1-Section. If we look in the song finders in the Warbler Guide, or if we enter these three qualities into the Warbler Guide App filter, guess what? We get a single bird! That bird is Prairie Warbler.

Song #2: Wilson’s Warbler

Listen to the song and compare it to the spectrogram:

spectrogram of wilson's warbler song

What Is the Sound Quality?  There are a lot of repeated Elements here, but they are relatively far apart, so they’re not too fast to count. That means this is not a Trill, but just a song with a series of Clear Elements.

wilson's warbler

A clear, falling, 1-section song: Wilson’s Warbler. Photo by Scott Whittle.

What Is the Pitch Trend? Overall this song has a Falling pitch. As a side note, you might notice a subtle shift downward in the second half of the song—that’s a good indicator for many Wilson’s songs.

How Many Sections Are There? This a simple, one-Section song.

So our final description is a Clear, Falling, 1-Section song. (One extra thing to notice is that the clear, separated notes have a sharp or staccato quality.) If you plug these characteristics into the Warbler Guide app using the filter feature, here’s the result:

demo of warbler guide app filtering feature with wilson's warbler

There are no other warblers that have 1-Section, Clear, Falling songs, so this description is diagnostic in both the East and West.

Song #3: Northern Parula

Listen to the song and compare it to the spectrogram:

northern parula song spectrogram

What Is the Sound Quality?  Unlike Wilson’s, this bird makes a true Trill. We can tell it’s a Trill in the spectrogram by the series of closely packed near-vertical lines—notice that there are far more than 11 Elements per second, which indicates that it’s too fast to count. But now notice that there is a second section in the song, and that section is just a single Clear Element. Because the song has two qualities, we’ll call it Partly Trilled.


A trilled, rising, 2-section song: Northern Parula. Photo by Scott Whittle.

What Is the Pitch Trend? The first Section of this song is clearly rising, and the second doesn’t change that much, so we’d call this a Rising song.

 How Many Sections Are There? We can see two Sections here: first there is a long Trill, with a Rising pitch trend. But then there is a very different, fast, clear, up-down Element to finish the song—that’s the second Section.

So this is a Partly Trilled, Rising, 2-Section song. Once again, this song has a diagnostic combination: a Rising Trill with a clear up-down element at the end can only be Northern Parula. In fact, all of Northern Parula’s songs end with that distinct, clear, higher up-down note, which makes it a very handy diagnostic quality to know about.

Happy Warblering! 

So by looking at three basic qualities—Sound Quality, Pitch Trend and Structure—we can finally make an accurate description of a song, and often find things about it that identify the bird to species.

You can use the answers in combination with our book and app to quickly find the bird you’re hearing. Even for non-warblers, applying these questions will help you hear details in songs that will make you a much more effective listener, and a much better birder! And if you’d like to learn more songs—download this guide to the songs of eight species, each of which has something diagnostic about it.

warbler guide authors tom stephenson and scott whittle

Tom Stephenson and Scott Whittle.

Happy Warblering!

Scott Whittle and Tom Stephenson are the authors of The Warbler Guide and the Warbler Guide app, from Princeton University Press. Warbler recordings are via the Cornell Lab’s Macaulay Library.

 More help learning bird songs:


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