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By Hugh Powell

Migratory songbirds enjoy the best of both worlds—food-rich summers and balmy winters—but they pay for it with a tough commute. Their twice-a-year migrations span thousands of miles and are the most dangerous, physically demanding parts of their year.

Surprisingly, for many North American species the best route between summer and winter homes is not a straight line, according to new research published in the Proceedings of the Royal Society B. In spring, the study shows, birds follow areas of new plant growth—a so-called “green wave” of new leaves and numerous insects. In fall, particularly in the western U.S., they stick to higher elevations and head directly southward, making fewer detours along the way for food.

“We’re discovering that many more birds than anyone ever suspected fly these looped migrations, where their spring and fall routes are not the same,” said Frank La Sorte, a research associate at the Cornell Lab of Ornithology. “And now we’re finding out why—they have different seasonal priorities and they’re trying to make the best of different ecological conditions.”

The research—the first to reveal this as a general pattern common to many species—may help land managers improve conservation efforts by improving their understanding of how birds use habitat seasonally.


The Rufous Hummingbird and Lazuli Bunting are two of the 26 western species in the study. Rufous Hummingbird by Brian Hampson; Lazuli Bunting by Todd Steckel, both via Birdshare.

“All this information helps us understand where we should focus conservation across time,” La Sorte said. “Then we can drill down and make local and regional recommendations. In the West particularly, the systems are very complicated, but we’re starting to build a nice foundation of knowledge.”

In a 2013 study, La Sorte and his colleagues discovered that many species of North American birds flew looping, clockwise migration routes. But they could only partially explain why. For eastern species, it was clear from atmospheric data that the birds were capitalizing on strong southerly tailwinds in spring over the Gulf of Mexico and less severe headwinds in fall. By adding the effect of plant growth, the new study helps explain why western species also fly looped routes.

The study examined 26 species of western birds, including the Rufous Hummingbird and Lazuli Bunting, and 31 species of eastern birds such as the Wood Thrush and Black-throated Blue Warbler. Birds on both sides of the continent showed a strong tendency to follow the flush of green vegetation in spring.


The Wood Thrush and Black-throated Blue Warbler are two of the 31 eastern species in the study. Wood Thrush by Kelly Colgan Azar; Black-throated Blue Warbler by Mitch Vanbeekum, both via Birdshare.

In the relatively continuous forests of the eastern U.S. this tight association with green vegetation persisted all summer and into fall. In the West, however, green space occurs along rivers and mountains, and is often isolated by expanses of desert or rangeland.

“Western migrants can’t necessarily cross big stretches of desert to get to the greenest habitat when it’s the most green,” La Sorte said. “So in spring, they stick to the foothills where insects are already out. But in fall they tend to migrate along browner, higher-elevation routes that take them more directly south.”

For decades scientists have known that some herbivorous species, including geese and deer, follow the “green wave” of spring vegetation on their northward migrations. La Sorte’s study is the first to extend that idea to insectivorous species, which are tiny (most weigh an ounce or less) and much harder to study using tracking devices.

The researchers solved that problem by using sightings data—lots of it—to substitute for tracking data. They analyzed 1.7 million crowdsourced bird checklists from eBird, a free online birding-list program, to construct a detailed picture of species occurrence for each week of the year. Then they used satellite imagery to determine the ecological productivity—or amount of new plant growth—across the U.S.

What emerged was a composite picture of where each species occurred, week by week, that the scientists then compared with satellite-derived estimates of where the greenest or most productive habitats were.

“Up till eBird data became available, people have had to look at migration on a species by species basis, by tracking individual birds,” La Sorte said. “We’re bringing in the population perspective using big data, and that’s enabling us to describe general mechanisms across species.”

In addition to La Sorte, the paper’s authors include Daniel Fink, Wesley Hochachka, and Steve Kelling of the Cornell Lab, and John DeLong of the University of Nebraska, Lincoln. The research was supported in part by grants from Leon Levy Foundation, Wolf Creek Foundation, and the National Science Foundation.

Related research on looped migration strategies:

(Top image: Rufous Hummingbird by Lois Manowitz via Birdshare)

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The idea of conservation brings to mind urgent actions: the race to save endangered species. But even more important is the goal of keeping common species common, the conservation equivalent of “an ounce of prevention is worth a pound of cure.” There’s no more potent reminder of this than the Passenger Pigeon, whose populations flatlined before anybody could reverse the declines.

With that in mind, the authors of the 2014 State of the Birds report analyzed North American bird populations for evidence of sharp recent declines among species that have always been numerous. These are early warning signs—clues that a habitat may be in trouble. By turning our attention to these problems, we may be able to identify the cause and turn around the trend before a population decline becomes irreversible.

The result is Common Birds in Steep Decline, a list of 33 common species compiled by scientists from the North American Bird Conservation Initiative. Long-term monitoring surveys indicate that each of these rapidly declining species has lost more than half its global population over the past four decades. This list complements the 2014 Watch List, which covers 228 species that are endangered, threatened, or at risk of becoming endangered.


List of Common Birds in Steep Decline:
(Links take you to the All About Birds species guide.)


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click to read the State of the Birds 2014 report

The 2014 State of the Birds report was released today in a ceremony at the steps of the Smithsonian Institution. The report takes inspiration from the story of the Passenger Pigeon: a symbol of both America’s natural bounty and its fragility. It was once the most abundant bird in North America, but it declined from billions of birds to zero in half a person’s lifetime.

The authors of the report—experts from 23 of the top bird science and conservation groups in the nation—believe that the health of bird populations foretells the health of larger ecosystems, and that efforts to conserve birds will result in a better environment for all.

They conducted the most comprehensive review of long-term trend data for U.S. birds ever assembled—and the results are both unsettling and hopeful. Bird populations are declining across several key habitats—particularly aridlands, grasslands, and forests; but strong conservation action in wetlands has paid great dividends. There’s lots to be done, but the good news is that conservation works.

What Does the State of the Birds 2014 Reveal?

  • Conservation Works: Grassland restoration through the Farm Bill has aided the region’s birds; wetland conservation has reversed the declines of waterfowl; coastal wetland restoration has provided resilience during major storm surges.
  • We Must Keep Common Birds Common: The report identifies 33 Common Birds in Steep Decline. Like the Passenger Pigeon, these are familiar birds we may take for granted now—but they have shown at least a 50 percent decline in the last half-century. Download a PDF of Common Birds in Steep Decline.
  • 228 Species on the Watch List: The Watch List includes federally endangered or threatened species, plus species that showed signs of severe population declines in the report’s analysis of of long-term (1966–2012) population data. Download a PDF of the Watch List.
  • Key Habitats in Danger: In clear trouble, based on the report’s analyses, are birds of the West’s aridlands; the native forest birds of Hawaii; the seabirds of the open ocean; the grassland birds of the middle of the continent; shorebirds of our coasts.
  • The Data You Provide Are Priceless: The State of the Birds 2014 analyzed decades of data from the Christmas Bird Count and Breeding Bird Survey to measure trends for hundreds of bird species—all data provided by enthusiastic, skilled, volunteer birders like you. Nowadays we have the Cornell Lab’s eBird project to make contributing data easy anywhere, at any time. The sightings contributed to citizen-science programs like these are an irreplaceable, indispensable part of understanding our world and planning for the future. We are grateful to everyone who participates.
  • We Know What Works: Just a few specific actions, broadly applied, would benefit bird populations in many places. Habitat loss is the number one cause of declining populations; conservation and restoration are key. Other problems include energy development, recreation in sensitive habitats, the introduction of invasive species, and climate change.

The State of the Birds report is the product of 23 agencies and organizations, including more than 70 individuals. The project lead was Alison Vogt of the Association of Fish and Wildlife Agencies. Cornell Lab participants included Ken Rosenberg, who chaired the science team; Gus Axelson, who edited the report; Ashley Dayer, who served on the communications team; Joanne Avila, who designed the report; and Stef den Ridder, a Bartels Science Illustration Intern, who painted the cover illustration.

Visit the State of the Birds website to read the full report and to download a PDF copy.


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By Pat Leonard

One of the most beautiful experiences in nature may be the sight and sound of thousands or even millions of shorebirds bursting into flight, dipping and wheeling as a coordinated unit, not once colliding with each other. But with worldwide shorebird populations declining across the board, it may be a spectacle future generations get to witness all too rarely.

To celebrate the amazing migrations of shorebirds, and to raise awareness of the challenges they face, the first ever World Shorebirds Day is taking place on September 6, 2014. Participants are being asked to count shorebirds, either on their own, at scheduled events, or at specific shorebird hotspots—and to report their counts through eBird.

The majority of shorebird species can be found near shallow water and include plovers, sandpipers, stilts, avocets, oystercatchers, shanks, snipes, and woodcocks.

“It’s that group of birds which are largely found next to the shore, whether it’s beach shores or inland wetland shores, but they do occur in other habitats as well,” says Rob Clay, director of the Western Hemisphere Shorebird Reserve Network. “Some species are grassland dependent, others are forest dependent; there are even a few species that occur in arid habitats. They may be found on the coast or at 4,000-plus meters up in the Andes.”

And they are clearly in trouble. Half the species that regularly occur in the United States and Canada are either highly endangered or of special concern, according to the U.S. and Canadian Shorebird Conservation Plans. In South America, of 34 breeding species, 32% have been identified as highly endangered or as a species of high concern, according to Clay. The new 2014 State of the Birds Report, being released September 9, includes a call for international efforts to halt the steep decline in shorebird populations. What’s happening in the Western Hemisphere is magnified in the Eastern Hemisphere where pollution and development-fueled habitat loss have put species such as the Spoon-billed Sandpiper on the brink of extinction. The odds have been stacked against shorebirds for a long time.

“As a group they tend to have small global populations compared to a lot of other species,” says Ken Rosenberg in the Cornell Lab’s conservation science department. “Some of them number in just the tens of thousands instead of millions.”


The Red Knot faces many perils along its long migratory journey. Click to see a larger version of this poster on the U.S. Fish and Wildlife Service website).

Those low numbers reflect a legacy of hunting in the last century from which some populations have never recovered. The Eskimo Curlew was hunted to extinction. Shorebird hunting in the Caribbean and northern South America continues today and this is where some of the steepest population declines are occurring.

Another reason for shorebird vulnerability stems from their spectacular long-distance migrations—some species travel from one end of the world to the other, from breeding grounds in the high Arctic to wintering grounds in Patagonia or New Zealand. They flock together at key stopping points along the way. Red Knots epitomize the vulnerability this behavior presents.

“Almost the entire eastern North America population of Red Knots stops in Delaware Bay for one week during migration,” Rosenberg says. There, the knots have historically fueled up on horseshoe crab eggs—a food source that has crashed from overfishing. “If they don’t get enough food at that spot they literally can’t make it up to their Arctic breeding grounds and that entire population can’t breed. They’re highly vulnerable because of these bottlenecks at migration stopover points where they congregate. ”

That’s why the shorebird reserve network has adopted a conservation strategy that focuses specifically on these critical stopover points. While flocking to these sites makes some shorebirds more vulnerable to population declines, Rob Clay says that same behavior can be a positive for conservation.

“If you can safeguard the critical network of sites that the birds need,” Clay says, “then you can essentially ensure the maintenance or restoration of their populations.”


Critical shorebird migration sites included in the Western Hemisphere Shorebird Reserve Network. For a more detailed map of the network, view the WHSRN’s interactive Google map. (Image courtesy of WHSRN.)

The Western Hemisphere Shorebird Reserve Network currently includes 89 sites in 13 countries, though Clay says there are probably 400 to 500 key sites throughout the Western Hemisphere. Becoming part of the network includes a voluntary commitment from landowners to take the needs of shorebirds into consideration in their management of the sites.

Restoring shorebird populations benefits humans as well, because it may preserve wetlands that act as a buffer during extreme weather, which is predicted to become more commonplace because of climate change. After an earthquake and tsunami devastated the area of Concepción, Chile, a few years ago, Clay notes that the communities least impacted were located behind the one small coastal wetland that remained in the area.

“That really underlined the value of coastal wetlands as a buffer,” says Clay. “Up until that point, the wetland had been slated for development. Those plans were stopped and the area is now, hopefully, about to become a protected area.”

Though the challenges may seem overwhelming, individuals do have a role to play in conserving shorebirds simply by reporting them to eBird.

“That’s actually one of the simplest ways that anybody who is interested in shorebirds can help,” notes Clay. “Just reporting observations through eBird enables us to build up a much better understanding of where the shorebirds are and when and what types of habitat they’re using. The house is not entirely burned down as yet but there’s a pretty significant fire raging through it. And the time to act is now before it is too late.”

What’s it like to study shorebirds? This video takes you to the Alaskan tundra for a day-in-the-life of a shorebird researcher:

For more information on shorebirds:

(Top image: Red Knots by B.N. Singh via Birdshare.)

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