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By Pat Leonard

The family of cotingas includes some of the brightest, most ear-splitting, oddest-looking, least-understood birds on the planet. Some have bulbous crests, long fleshy wattles, or Elvis-worthy pompadours. Others have shockingly bright feathers: electric blue, deep purple, or screaming orange. How did they get that way? What twisting evolutionary path resulted in the origin of more than 60 species that are so variable you’d be hard pressed to understand how they could possibly be related each other?

Some of these questions can now be answered, thanks to a new evolutionary “tree of life” (technically known as a phylogeny) for the cotingas, which are native to Central and South America. The door is now open to new discoveries about this amazingly diverse group of birds.

“They are so variable that even defining just what a cotinga is has been a difficult question,” says lead author Jake Berv, a Ph.D. student in the Fuller Evolutionary Biology Lab at the Cornell Lab of Ornithology. “Our study provides comprehensive insight into how nearly all the cotinga species are related to each other going all the way back to their common ancestor. No previous attempts to understand the evolutionary history of this group have included genetic samples from nearly all the existing species.”

Berv began sequencing DNA samples and compiling data in late 2010 while working as a lab technician at Yale University with coauthor Rick Prum, a leading expert on cotingas. For species whose DNA had never been sequenced before, the researchers took small tissue samples from the toe pads of museum specimens.

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This circular rendition of the “tree of life” shows nearly all the sizes, colors, and adaptations for the continga family of birds radiating outward from the center and its common ancestor. Both males and females are shown except where plumage for both is the same. Illustrations are reproduced with permission from the Handbook of the Birds of the World. Vol. 9. Cotingas to Pipits and Wagtails, Lynx Edicions 2004. Click on the image for a full-screen view.

Understanding how one species is related to another within this group allows scientists to trace the evolution of specific traits and behaviors. For example, Berv and Prum wanted to learn if the evolution of differently colored males and females in this bird group (known as sexual dimorphism) is directly linked to a breeding system in which males have multiple mates (known as polygyny—a fairly widespread practice in some birds, including the familiar Red-winged Blackbird).

Darwin first theorized that the increased pressure of sexual selection in polygynous birds spurred the development of color differences between the sexes. That is to say, in situations where males have the chance to mate with many female birds, there’s pressure for them to step up their game by adopting brilliant colors. This appears to be true for many species—but not the cotingas. When Berv and Prum examined patterns of evolution for these two traits across their new tree of life, there was no significant match. There have been many more evolutionary changes in color than there have been for breeding system. Berv says these traits may be evolutionarily “decoupled” in the cotingas.

However, sexual selection appears to have played a role in the evolution of sexual differences other than color in some cotingas.

“In one case, the Screaming Piha, the males and females look alike but the male sings one of the loudest songs on the planet,” says Yale’s Rick Prum. “That means male-female plumage difference alone is not evidence for sexual selection because sexual selection is also driving other traits such as voice and behavior.”

Though the researchers didn’t find a link between the coloration of males and females and the evolution of polygynous breeding systems, Prum says some form of sexual selection almost certainly did play a role in the eye-popping colors some cotingas display. Some species have evolved a variety of colors seen only in this group of birds, such as the glowing orange cowl of the Andean Cock-of-the-Rock, the fluorescence of the Turquoise Cotinga, or the blue-and-maroon combo of the Banded Cotinga.

“Some cotinga colors are not produced by pigments,” Berv explains. “Some of these birds have evolved cool nanoscale feather structures made with feather protein molecules. The nanostructures scatter light and produce visible color the birds use in sexual signaling.”

Figuring out how these feather structures evolved is an area of future study. In fact, “the sky’s the limit,” according to Prum, who notes other areas of study could include the evolution of elaborate courtship displays, clutch sizes, or the vocal organs that produce the ear-splitting sounds of the raucous bellbirds and pihas. Even the color question can be studied on a much more refined scale.

“Rather than just asking whether males and females of a species are dimorphic, yes or no, we will next measure various color patches and quantify brilliance,” says Prum. “For example, male and female robins look different, so that would be a ‘yes’ for dimorphism. But they’re not as different as the male and female Scarlet Tanager. On the ‘yes-no’ scale they would be scored the same. If we actually measure the colors we’d be able to say ‘Wow, males and females of one species are really a lot more different than the other.’ That would reflect the impact of sexual selection a lot better.”

“One of the biggest analytical differences between what we’ve done and past work is that we used a ‘species tree’ approach, which is potentially more accurate than what is typically applied to genetic data,” Berv says. “We ran our data through more traditional types of analyses as well, and all of them strongly supported a consistent evolutionary ‘tree of life.’ We hope other scientists who are interested in these birds take our phylogeny and do all sorts of great things with it.”

The paper, A Comprehensive Multilocus Phylogeny of the Neotropical Cotingas (Cotingidae, Aves) with a Comparative Evolutionary Analysis of Breeding System and Plumage Dimorphism and a Revised Phylogenetic Classification was published in the journal Molecular Phylogenetics and Evolution.

The research was paid for by W. R. Coe funds from Yale University and supported in part by the facilities and staff of the Yale University Faculty of Arts and Sciences High Performance Computing Center. The DNA work was performed at Yale; Berv did the data analysis and writing at the Cornell Lab, where he is a Ph.D. student in the Fuller Evolutionary Biology Lab.

For more information on bird evolution:

(Photos: Andean Cock-of-the-Rock © Lorraine Minns; Turquoise Cotinga © Juan Carlos Vindas; Three-wattled Bellbird © Andrew Spencer; Red-ruffed Fruitcrow © Daniel Field; Red-crested Cotinga © Glenn Bartley; White-tipped Plantcutter © Daniel Field; Bare-throated Bellbird © Ben Tavener; Spangled Cotinga © Greg Hume; Bearded Bellbird © Steve Garvie; Purple-throated Fruitcrow © Eduardo Iñigo-Elias; Purple-throated Fruitcrow © Daniel Field)

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By Pat Leonard

If you have an ear for dialects, you can probably take a good guess as to a person’s origins. The same words spoken by people raised in Brooklyn, Boston, and Bakersfield tend to sound different (though still recognizable). The tone and pitch of words are often influenced by the sounds heard and learned from within each individual’s neighborhood and family.

Family and neighbors also play a key role in the songs sung by Western Bluebirds, according to a two-year study published in the journal Animal Behaviour. Conducted at the Hastings Natural History Reservation in Carmel Valley, California, the study found that Western Bluebirds not only share their songs with relatives but with unrelated bluebirds that live nearby—i.e., the neighbors.

The researchers found that, no matter where they were raised, when male Western Bluebirds move to their own territories they share songs with their closest neighbors. That’s true whether the other birds are related or not, though they do a bit more sharing with nearby relatives. On the flip side, they rarely share notes with non-neighboring birds, even if they are related.

“It’s like speaking the dialect of the neighborhood you move into,” says study author Çağlar Akçay who led the research during his postdoctoral work at the Cornell Lab of Ornithology. “We wanted to find out if the birds learn from and share songs only with relatives—in which case the songs would function as a way to identify family—a ‘family signature.’ But if they learned and shared songs with nonrelatives too, then the songs could not stand alone as a means of recognizing kin.”

As a cooperatively breeding species, it’s important for a Western Bluebird to recognize close family. Male Western Bluebirds tend to breed next door to their parents, brothers, and sometimes grandparents, often sharing a boundary with a male relative’s territory. If dispersed males are unable to breed on their own, they will help raise the young in the nest of their parents, a parent and step-parent, a brother, or even a grandfather. Western Bluebird territories are variable but the longest song-sharing distance measured to date at the Hastings Reservation is 2.2 miles (3.6 km). A maximum sharing distance has not been determined.

Though females of the species also sing, they disperse farther away and only one-fifth as many stay in the study area. Also, females don’t sing during the pre-dawn chorus, and consequently they are harder to record. For these reasons, female Western Bluebirds were not part of this study.

Male Western Bluebird songs were recorded for the study during the song-filled early dawn. Because the human ear isn’t up to the job when it comes to noting the subtle differences among the bluebird songs, the recordings were processed through sound analysis software to produce images, or spectrograms, of each note. Three independent judges compared spectrograms visually and agreed 98% of the time on which songs were shared and which were not. (More on how to read spectrograms.)

“On average, Western Bluebirds have eight or nine ways of making their pew sound and a couple variations for their chuck notes,” Akçay says. “These are the building blocks of their song.”

Akçay says it is the “acoustic signature” of each note type that matters for identification—meaning how the sound frequency is modulated. One note might have a very steep increase in frequency while another might be more gradual.

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Spectrograms gave the researchers a visual way to compare bluebirds’ songs. Click the player below to hear the song and follow along on the spectrogram. Source: Macaulay Library; recordist: William R. Fish. (Recordings in this blog post were not used in the research.)

Hear the song:

 

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By comparing this recording with the previous one, you can see subtle differences between the songs of Western Bluebirds. The differences are harder to pick out without the help of a spectrogram. Click the player below to hear the recording. Source: Macaulay Library; recordist: Thomas G. Sander.

Hear the song:

 

It’s not clear what advantage, if any, the bluebirds might gain by sharing songs with nonrelatives but Akçay says a number of theories could be investigated. Studies of other bird species have suggested that shared songs can be used to signal aggression between males, to indicate a male’s fitness for breeding, or as a way to reduce or avoid aggression among birds that are known to each other.

So what happens if a bluebird changes its territory or its neighbors change when new birds move in next door? Preliminary findings suggest the birds don’t completely change their repertoire but they do change.

“We actually had one individual that made a really big move from one year to the next,” Akçay says. “We had recordings of him both years and he kept 80 percent of his songs after the move. The other 20 percent were new songs adopted after the move.”

Akçay concludes, “The major takeaway here is that Western Bluebirds probably identify kin in a linear process—first noting through song that the other bird is a specific individual such as ‘Joe,’ or ‘Fred,’ then further noting, ‘Joe is my brother’ or ‘it’s Fred the neighbor who is not related.’ This second stage of classification may be helped by other cues such as behavior, appearance, and even smell in addition to shared song.”

The study is part of a 30-year research program conducted at Hastings Reservation by Janis Dickinson, who directs the Cornell Lab’s Citizen Science program and is a Cornell University professor. This long-term study, funded in part by the National Science Foundation, has provided a wealth of knowledge about social behavior on a large sample of birds with known social relationships, making these kinds of discoveries possible.

The study, Song sharing with neighbors and relatives in a cooperatively breeding songbird, was coauthored by Akçay and Dickinson with students Katherine L. Hambury (Cornell Lab), J. Andrew Arnold (Cornell Lab and Old Dominion University), Alison M. Nevins (Cornell Lab), all of whom contributed to recording, field experiments, and classification of vocalizations.

More about bird song:

(Top photo: Western Bluebird by Stephen Parsons via Birdshare)

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Join Jack Jeffrey, photographer and wildlife biologist, in an entertaining and informative program about Hawaii’s wonderful forest birds, the problems they face, and the extensive efforts being made to protect these amazing forest creatures from further decline and extinction.

The talk took place on September 29, 2014. 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! If you missed any talks, please see our index of archived livestreamed seminars.

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Artwork by Luke Seitz

Scientists are learning more than ever about autumn bird migration, but there are still plenty of unsolved mysteries. What forces dictate their departures and arrivals? Why do they choose the routes they do? And why do some birds end up far off course?

In the past, rare sightings have been chalked up as vagrants—anomalies of bird movement that couldn’t be predicted and might never happen again. But as time and data points have piled up, it’s become clear that many rare sightings are the result of regular, if infrequent, patterns. As we gain an understanding of these patterns, we can use them to unravel migration mysteries and know when and where to look for rarities.

Two of the programs leading the way in this effort are BirdCast and eBird. The eBird project provides the raw sightings data (when bird watchers like you report your sightings to the project). BirdCast combines the sightings data with meteorological data and weather surveillance radars (which can “see” birds just as they can “see” raindrops—as in the map above). These data sources allow BirdCast’s team to develop weekly, region-specific predictions to let North American birders know which birds to look for and when—as well as to understand rarer phenomena like these eight migration mysteries:

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What’s that “peep” in the night? Ever go outside on a crisp September evening and hear what sounds like a spring peeper in the sky? Except, it’s fall… and frogs don’t fly? Lots of songbirds migrate at night and call to each other with very short, faint notes. The calls of Swainson’s Thrushes are among the most distinctive of these “night flight calls,” and they are loud enough that you can actually hear the birds as they fly overhead. Your best bets for hearing this peep in the night sky will come immediately after a cold front passes, particularly when birds fly into areas with poor visibility (like fog) and light pollution where calling increases dramatically (birds tend to call more frequently when disoriented). See this post to hear the call notes and learn how to identify them.

NLapwingWhere did all those Northern Lapwings come from? After Hurricane Sandy in late October, 2012, dozens of Northern Lapwings showed up in the northeastern U.S. Never before had a tropical system’s passage brought such a bounty of this visitor from Eurasia. In fact, most hurricanes tend to take American birds and deposit them in Europe, not the other way around. But by analyzing meteorological data, the BirdCast team discovered that the hurricane’s counterclockwise circulation was augmented by high pressure over the North Atlantic and winds blowing from Europe. The result was east-to-west winds that delivered many American birders a new species for their life list. See the full story on vagrants from Sandy in the BirdCast archives.

FTFlycatcher2What drives cameo appearances of Fork-tailed Flycatchers in fall? These spectacular birds are one of the species birders look forward to seeing when they plan a trip to Central or South America, where they are fairly common. But almost every autumn (especially in September) the tables turn and a few Fork-tailed Flycatchers come to visit birders in the eastern U.S. On closer examination, these rarities usually belong to the savana subspecies, which breeds from Brazil to Argentina and winters in Amazonia. In other words, these birds don’t belong in the U.S. The evidence suggests that when most Fork-tailed Flycatchers are migrating, some individual birds overshoot and wind up over the ocean, where they then fly downwind and end up making landfall in the U.S.

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Orange and white colors show where Blackpoll Warblers migrate in the spring and then in the fall, en route to and from Canadian breeding grounds. The spring route covers much of the East, whereas in fall most birds leave from the Northeast and Mid-Atlantic, and fly directly to South America. See a larger map at eBird.

Where did all the Blackpoll Warblers go? Blackpoll Warblers are fairly common spring migrants all the way up through the eastern states. Not so in fall, when they are rarely sighted in states south of the mid-Atlantic. That’s because their main fall migration route takes them out over the open ocean. The birds often fly nonstop over the Caribbean en route to their winter grounds in South America.

CSparrowWhy do Chipping Sparrows migrate twice? We often think of migration as a straight shot from breeding grounds to wintering grounds. But quite a few species—including the familiar Chipping Sparrow—take a detour to accommodate their molt. These so-called molt migrants take a short migration trip to one area where they grow new feathers. Then they resume their migration to wintering grounds. For instance, Chipping Sparrows in the Front Range of Colorado migrate eastward to molting sites such as the Pawnee National Grasslands, then continue to Mexico.

PGallinuleWhat are Purple Gallinules doing in Newfoundland? When Purple Gallinules—which typically live in subtropical and tropical marshes—began showing up in Portugal, Maine, Newfoundland, Iceland, and Ireland, the BirdCast team took notice. They think an autumn drought in the Caribbean caused many gallinules to disperse in the winter of 2013–2014. Because Purple Gallinules are very strong fliers, and sensitive to changes in wetlands, they are very prone to wandering way out of their traditional range. And thanks to the now worldwide network of birders entering their sightings into eBird, the BirdCast team is able to convert these unusual sightings into data.

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What’s a Blue-footed Booby doing in California? The Golden State boasts a huge collection of cool birds, but the Blue-footed Booby is not usually one of them. It’s a tropical seabird typically found along the Mexican coast and south to South America—but in fall of 2013, many dozens of Blue-footed Boobies were reported along the California coast. When the BirdCast team looked into meteorological patterns, it appeared that unusually warm sea surface temperatures may have caused the move, along with a similar pattern in Elegant Terns. The suggestion is that prey fish moved north to find cooler waters, and so the boobies moved with them.

Why do Long-billed Curlews winter in both California and Mexico? Long-billed Curlews breed in grasslands and open country of the central and western U.S. In winter, you can find them in coastal and interior California, as well as in landlocked wetlands of the Southwest and Mexico. By putting together species distribution models from eBird data, it appears these two populations may employ different migration routes. Curlews from the Great Basin may travel westward to winter in California, while Great Plains curlews travel south to reach Mexico.

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(Illustrations by Luke Seitz. BirdCast is a joint project of computer scientists and bird biologists at the Cornell Lab, Oregon State University, University of Massachusetts, Amherst, and other partners.)

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