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A Red-necked Grebe on a small lake in Maryland, March 2014. Photo by JMC Nature Photos via Birdshare.

By Gustave Axelson and Marshall Iliff

For the past six weeks, the Cornell Lab’s eBird team has been buzzing about the potential this spring for inland fallouts of Red-necked Grebes around the Appalachians region. That happened during the frigid winter of 2014. And in early 2015, as thermometers seemed stuck in the single digits, it looked like all was set for a repeat.

Fallouts are the stuff of birding legend—a phenomenon where bad weather forces masses of migrating warblers, orioles, and tanagers to land for cover all at once. They’re typically seen along the Gulf Coast. In spring 2014, fallouts of a different kind occurred throughout the Northeast, when eBirders reported Red-necked Grebes scattered on inland small ponds and rivers—far away from their usual big-water haunts on the Great Lakes and Eastern Seaboard at that time of year.

Looking back at what caused this inland grebe fallout, the eBird team noticed that the 2014 Great Backyard Bird Count, in February, had tallied unusually high counts of Red-necked Grebes on inland bodies of water, from New England to North Carolina and Ohio to Tennessee. In a normal winter, the majority of Red-necked Grebes overwinter along the Atlantic Coast in the Northeast, with some smaller populations overwintering on Lake Ontario. What were so many doing inland?


In winter of 2014, ice cover on the Great Lakes forced Red-necked Grebes to gather on inland lakes in higher than usual numbers. Curiously, the cold winter of 2015 did not produce the same pattern. Darker shades of purple indicate areas with more Red-necked Grebe sightings (data from eBird).

The winter of 2013-14 was historically cold, and Great Lakes ice cover exceeded 92 percent (50 percent ice cover is about average). With America’s easternmost Great Lake just about frozen over, the grebes were forced off of Lake Ontario and headed south and east to find open water—hence the high inland grebe counts in the GBBC. And then in March 2014, as grebes migrating from the Atlantic Coast looked for their traditional rest stop on Lake Ontario, they instead found ice and probably had to reverse course, further bolstering the numbers of inland grebes. Since these grebes were probably short on fuel, fallouts ensued as these grebes landed on whatever open water they could find south and east of Lake Ontario.

Looking back further into the eBird data, this March pattern also happened in 1993 and again in 2003. And it looked like the same recipe for grebe fallouts was cooking up this year, with another epically cold winter and the Great Lakes again more than 90 percent frozen.

But as team eBird closely monitored the Red-necked Grebe reports in the East this winter and spring, the large inland congregations of grebes never materialized. What happened? There are a few possible explanations.

It could be that when Lake Ontario froze on consecutive years back-to-back, some grebes changed their behavior, as they learned not to attempt to winter on Lake Ontario. It is also possible that many of last year’s grebes that were forced off Lake Ontario died, either as a direct result of the freezing in February or because they were simply less healthy for their spring migration after the freezeout.

The two options above would explain the lack of a midwinter movement, but what about March? This year, despite high ice cover on the Great Lakes, large patches of Lake Ontario had opened up again in March. So grebes migrating from the Atlantic found open water at the right time take a rest on Lake Ontario on their journey back northwest toward breeding areas in Canada and Alaska.

As of now, it seems grebes are finding no interruptions to their regularly scheduled migration on the northwest shore of Lake Ontario. The lake is ice-free in the Toronto area, and on April 5 one dedicated Canadian birder carefully counted 1,529 Red-necked Grebes there on a single eBird checklist!

For more information:

Gustave Axelson is a Cornell Lab science editor; Marshall Iliff is a co-leader of eBird.

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palm warbler by Andrew Wood

Fully 98% of the Palm Warblers we see on migration and in winter began their lives in the boreal forest. Photo (taken in Florida) by Andrew Wood via Birdshare.

By Jeff Wells

In the northern reaches of North America lies a vast forest that extends from interior Alaska all the way across Canada to Newfoundland and the Atlantic Ocean. It provides the breeding grounds for billions of migratory birds each summer and is home to around one-quarter of the world’s remaining untouched forests. North America’s boreal forest contains a treasure trove of internationally significant ecological values, and it’s also the focus of one of the most ambitious conservation efforts anywhere on Earth.

facts about boreal birds

The combination of its intactness (about 80% is still relatively intact and free of industrial disturbance) and its vast networks of wetlands and waterways (millions of lakes large and small and around 25% of the world’s wetlands) makes this lush forest a summer breeding paradise for at least 325 bird species—nearly half of the species commonly found in the U.S. and Canada.

Some of the species that most excite birders around the United States during spring and fall migration owe much of their existence to the boreal forest. More than half of the wood-warbler species that can be found throughout the U.S. breed in the boreal forest. Some are almost entirely reliant on it, including the Palm Warbler (estimated 98% of its North American population), Tennessee Warbler (97%), Connecticut Warbler (91%), and Cape May Warbler (83%).

The millions of lakes and ponds sprinkled throughout the forest also make it a haven for waterfowl, supporting an estimated 80% of the waterfowl species found in the U.S. and Canada.

All in all, between 1 and 3 billion birds flock to the boreal each spring to nest over the summer, their numbers swelling to 3 to 5 billion once the young are ready for fall migration. More than 1 billion of these birds will settle in the United States to winter while many more pass through en route to warmer climes.

This U.S. Fish and Wildlife Service video helps illustrate the boreal forest’s importance to many bird species:

This is precisely why a coalition of bird and conservation organizations have joined together to call for the protection of at least half of this continental bird nursery. The Boreal Birds Need Half campaign is led by the Boreal Songbird Initiative and Ducks Unlimited; it includes the Cornell Lab of Ornithology, Audubon, and other leading organizations.

Equally important, it urges the use of high sustainability standards on industrial activity in remaining landscapes and the implementation of free, prior, and informed consent when engaging resident indigenous communities, many of which have resided in these boreal landscapes for thousands of years.

As recently as the early 90s, conservation biologists believed that setting aside as little as 10–12% of an ecological region would be sufficient to maintain the majority of species and ecosystem functions present (reports referenced here). However, modern conservation science has proven this target to be a considerable underestimate. Now, scientists contend that at least half of the boreal forest should be set aside from development. This figure is also in line with the long-term needs of boreal birds, many of which feature relatively widespread breeding ranges and require large expanses of healthy habitat.

The campaign is now seeking to enlist the power of the millions of birders across the continent. You’ll find more information about this issue and actions you can take at the Boreal Birds Need Half campaign website.

Dr. Jeff Wells of the Boreal Songbird InstituteJeff Wells is the senior scientist for the Boreal Songbird Initiative and a former scientist at the Cornell Lab of Ornithology.

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One species or two? Common Redpoll (left) by Sharon Watson via Birdshare, Hoary Redpoll (right) by Chris Wood.

By Gustave Axelson

The Hoary Redpoll is one of those hard-to-get lifelist-adds that can turn birders into Captain Ahab seeking a little whitish bird. The allure of these little ghost finches has drawn many a lister to places like Minnesota’s Sax-Zim bog—in the dead of winter—just for a chance to lock into a Hoary.

But new research by two scientists at the Cornell Lab of Ornithology presents genetic evidence that reopens questions about the species status of the Hoary Redpoll, long thought to be the frosty cousin of the Common Redpoll. In a paper published this week in the journal Molecular Ecology, Nicholas Mason and Scott Taylor of the Cornell Lab’s Fuller Evolutionary Biology Program show that Hoary Redpolls and Common Redpolls have no differences at all across much of their genomes.

“Based on the samples of DNA we examined for Common and Hoary Redpoll, they’re probably best treated as a single species,” Mason says.

In other words, should this new evidence similarly sway the American Ornithologists’ Union’s checklist committee, all the heroic efforts birders have made to add a Hoary to their life lists may be for naught.

The division of redpolls into different species dates back to before the Civil War. In 1861, legendary ornithologist Elliot Coues (one of the founding fathers of the AOU) described eight separate redpoll species based on their visual appearances. Over time the AOU consolidated Coues’ list, but Hoary Redpoll, which has a snow-white breast, was still considered a separate species from Common Redpoll, which has a brown-streaked breast.


The researchers compared the DNA of 77 redpolls. The evolutionary tree they reconstructed shows that the three redpolls intermixed extensively in their evolutionary past. If they were separate species the branches of the tree would be much more distinct, as shown for their close relative, the White-winged Crossbill. Adapted with permission from Mason and Taylor 2015, Molecular Ecology; White-winged Crossbill by Nick Saunders via Birdshare.

Mason and Taylor looked beyond the plumage into strands of the birds’ DNA in the most extensive look ever at the redpoll genome. Whereas previous genetic analyses of redpolls looked at just 11 regions of the genome (at most), Mason and Taylor examined 235,000 regions. (That impressive number is a testament to the exponential advances in DNA-sequencing technology, but the researchers are quick to note it’s still less than 1% of the total genome.)

In all, the duo compared DNA from 77 redpolls, including specimens from museums around the world, from the Museum of Vertebrates at Cornell University to the Natural History Museum of Geneva in Switzerland. They found no DNA variation that distinguishes Hoary Redpolls from Common Redpolls. Furthermore, another redpoll species found in Europe—the Lesser Redpoll—also had extremely similar DNA sequences. This extreme similarity among all the redpolls stands in marked contrast to studies of other groups of birds—such as Black-capped and Carolina Chickadees—which show differences at many regions of the genome.

In nature, one of the key differentiators among distinct species is assortative mating, that is, members of a group breeding with each other more often than they breed with members of another group. According to Mason, when it comes to Hoary, Common, and Lesser Redpolls, “There are no clear-cut genetic differences, which is what we would expect to see if assortative mating had been occurring for a long time.”


The three current species of redpoll—Common, Hoary, and Lesser—stretch around the Arctic in a continuous swath that isn’t necessarily apparent from a normal map projection. Adapted with permission from Mason and Taylor 2015, Molecular Ecology.

Instead, Mason says the world’s three redpoll species seem to be “functioning as members of a single gene pool that wraps around the top of the globe.”

But how could it be that Hoary and Common Redpolls look so different given that their genetic makeup is basically the same? For that answer, Mason and Taylor delved into the birds’ RNA. (A quick flashback to high-school biology: If DNA is like the body’s blueprints, RNA is like the construction foreman communicating the instructions to build physical features, like hair or feathers.)

The physical differences among redpolls are associated with patterns in their RNA, not their DNA. In other words, the variation we see in plumage and size is probably not a matter of genetic variation, but of genetic expression. It’s kind of like how two humans might have the same gene for brown hair, but one person’s might be lighter than the other’s—that gene is being expressed differently. In the same way, Hoary and Common Redpolls have remarkably similar sets of genes, but those genes are expressed differently, causing the plumage and bill-shape differences we see.

To look simultaneously at both DNA and RNA, Mason and Taylor sampled birds—some with highly streaked plumage, some with white plumage, and some with in-between markings— from a large flock that had gathered in a fellow Cornell Lab employee’s backyard in Cortland, New York. If Hoary and Common Redpolls had long been separate species, then the birds sampled should have mostly fit neatly into two categories, both by visual appearance and genetically. Instead, there were a few birds that definitely fit the visual description of what we call a Common Redpoll, a few birds that definitely fit the pattern for a Hoary Redpoll, and a lot of birds in the middle—with varying degrees of whitish breast and faint brown streaks.


The bird on the left is a classic dark, streaky Common Redpoll, while the bird on the far right is a snowy, small-billed Hoary Redpoll. But many birds lie in between these two extremes. The new research suggests all the Common–Hoary confusion over the years may have been justified. Photos, from left to right, by Sharon Watson, newfoundlander61, Guy Lichter, Stuart Oikawa, and Chris Wood.

“We didn’t find distinct characteristics to separate the redpoll types, but rather a continuum, or a progression, of physical traits,” Mason says. “And many redpolls were somewhere in the middle.”

Next, Mason and Taylor are planning to work their research into an official proposal for the AOU to lump Hoary, Common, and Lesser Redpolls into a single species, based on the genetic evidence. If accepted by the AOU’s Nomenclature Committee, the end result may sting for birders who see a Hoary Redpoll subtracted from their life list. But Taylor hopes his research will change the way people look at redpolls altogether.

“I think this makes them a more interesting bird,” he says. “It means they’re part of an exciting, complicated system that can make a single species look different across different parts of its range.”

For more on redpolls and phylogeny:

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Maps revealed that North American hummingbirds, like the Calliope Hummingbird, migrate along different routes each year, possibly in response to food variability. Photo by LAP75 via Birdshare.

By Jennie Miller

Imagine circling the Earth twice on foot while drinking your weight in flower nectar each day. That’s the human equivalent of what Calliope Hummingbirds do, by wing, twice a year, in their migrations between Washington and Mexico. How such small birds travel such immense distances has puzzled ornithologists for decades because hummingbirds are too tiny to wear GPS tags for tracking. Now finally, through the use of citizen science, researchers have mapped the daily movement of migrating hummingbirds, and outlined a path of hope for the species along the way.

Using data from the eBird citizen-science project, researchers patched together hummingbird sightings from more than 300,000 checklists across North America to track the central hub of migration over a five-year period. Based on the number of eBird sightings at different locations, researchers calculated the average location of hummingbird populations for each day. For example, of the estimated 2 million Calliope Hummingbirds in North America, some individuals were recorded by eBird participants during the study period from 2008 to 2013. Researchers used these sightings to then find the average location of all Calliope Hummingbirds each day and visualize overall movement of the species throughout migration.

“We could not have surveyed the entire United States 365 days a year,” explained Sarah Supp, a postdoctoral fellow at Stony Brook University and lead author of the study. “Citizen-science data gave us that.” The research team also included the Cornell Lab of Ornithology’s research scientist Frank La Sorte and was funded by NASA’s Biodiversity Program. Their study focused on 5 hummingbird species that migrate up to 2,500 miles across North and Central America: the Calliope Hummingbird, Black-chinned hummingbird, Broad-tailed Hummingbird, Ruby-throated Hummingbird, and Rufous Hummingbird.

Published in the January issue of Ecosphere, the maps revealed that the birds hopscotched between different stopover sites each year. For instance, over the five-year study, Calliope Hummingbirds shifted their central path of migration as far as 320 miles east or west between years, switching from routes focused around Tucson, Arizona, to Albuquerque, New Mexico, and from Bakersfield, California, to Las Vegas, Nevada.

According to Supp, this year-to-year variation suggests some “wiggle room” in hummingbird decision-making. The birds could be choosing sites with high-quality food, such as flowers with nectar to fuel their fast-paced metabolism. Such versatility may enable hummingbirds to respond as the rising temperatures of climate change alter the timing and location of flowering plants.

“Under climate change, one of the things we’re concerned about is mismatch in timing for migrating species,” said Supp. “If hummingbirds come north and the plants are already done flowering at the location where they’re expecting food, then that could be a problem.”

North American hummingbirds are especially vulnerable because they are so small, weighing the equivalent of two or three paperclips, and have such high metabolic rates, the fastest of all warm-blooded animals. These limitations prevent them from packing on large quantities of body fat to last them through migration. As a result, they feed continuously as they migrate, requiring frequent access to flowering plants with nectar throughout their route. “For some birds, going for extended periods without food means they get skinny or stressed,” said Catherine Graham, a principal investigator on the study based at Stony Brook, “but for a hummingbird, it could mean death.”

As climate change alters the availability of flowering plants, bird feeders may become an increasingly important source of food for migrating hummingbirds. “Feeders serve as a supplement to natural food for birds,” explained Emma Greig, project leader of the Cornell Lab’s Project FeederWatch. “Especially in extreme climate situations, like a harsh winter, feeders could play an important role in helping hummingbirds survive.”

With 10% of all hummingbird species worldwide threatened by extinction, the study offers optimistic news on the long-term survival of these beloved birds. Says Supp, “It tells us that hummingbirds will be flexible to a certain degree because they are potentially able to sense when it’s time to move, and that time may be different from year to year. It gives us some hope.”

For more on hummingbirds and bird migration:

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