‘Green wave’ explains migratory bird routes

1.7 million crowd-sourced bird checklists from eBird used to construct a detailed picture of species occurrence for each week of the year to help explain bird migration patterns

Team VCE watching a pair of Orchard Orioles in the early morning fog. Observations like these are entered into Vermont eBird.

Team VCE watching a pair of Orchard Orioles in the early morning fog. Observations like these are entered into Vermont eBird.

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.

“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.

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.”

Study: http://rspb.royalsocietypublishing.org/content/281/1793/20140984.abstract?etoc

Field Report: Final 2014 Bird Banding on Mt. Mansfield

Dusk in the Clouds on Mt. Mansfield, VT / K.P. McFarland

Dusk in the Clouds on Mt. Mansfield, VT / K.P. McFarland

VCE wrapped up its 2014 mountain bird field season with an overnight visit to our Mt. Mansfield ridgeline study site on Tuesday.  Arriving at the upper toll road parking lot ~5 pm, we were greeted by chilly, damp conditions, but also by calling Bicknell’s Thrushes (BITH), which annually undergo a resurgence of vocal activity in mid-September. We set up 17 mist nets, mostly on the Amherst and Lakeview trails, and ran them until dusk.  BITH calls pierced the skies until darkness fell, and a few birds sang briefly.  The frequency and vigor of vocalizing was nowhere near that of 3 months ago, but the chorus was a far cry from the eerily quiet evening of our visit in late July.

The ridgeline was still bathed in clouds when we returned at 5:45 am to open nets, and temperatures hovered in the raw low 40s F.  BITH put on a solid dawn chorus, as we heard 16-18 birds total. Swainson’s Thrushes were nowhere to be seen or heard.  Our nets started filling, and by noon we had captured 76 birds. Yellow-rumped Warblers were by far the most abundant species on the ridgeline, and in our nets, but BITH may have been second, judging from both captures and birds heard vocalizing.  Of the 13 BITH we mist-netted, 5 were recaptures of adult males from June and July (one a bird originally banded in 2011).  Our total of BITH captures for 2014 ended up at 57, possibly a single-season record over our 23 years of banding.

Steve Faccio removing a Bicknell's Thrush from a mist net for banding. / K.P. McFarland

Steve Faccio removing a Bicknell’s Thrush from a mist net for banding. / K.P. McFarland

Overall diversity on the ridgeline was low, as we identified only 16 species during the morning, which included 2 Sharp-shinned Hawks and a single Peregrine Falcon.  One unexpected encounter was of 3 Ruffed Grouse flushed at ~3800 ft elevation on Tuesdayevening. Surprisingly, Black-throated Blue Warblers, which our fall migration banding study in the mid-1990s showed to be the most abundant transient species on Mansfield, were almost non-existent – we saw and netted only one bird.  [read more about our results from that study, http://www.vtecostudies.org/PDF/WB112.pdf].

Our combined capture totals for the 16-17th:

Black-capped Chickadee    1
Bicknell’s Thrush    13 (7 immatures, 1 new adult, 5 recaptured adult males)
Nashville Warbler    1
Blackpoll Warbler    6 (2 immatures, 4 adults)
Black-throated Blue Warbler     1 imm. female
Yellow-rumped Warbler    50 (41 immatures, 9 adults)
White-throated Sparrow    6 (3 immatures, 3 adults)
Dark-eyed Junco     8 (7 immatures, 1 adult)

Mist net in the fog. / K.P. McFarland

Mist net in the fog. / K.P. McFarland

A final note: there are very few cones on the balsam fir trees (and we saw or heard no red squirrels), so it’s likely that squirrel populations will again be low in 2015, leading to higher breeding productivity by BITH and other open-cup nesting species.  The biennial “boom-bust” cycle of cone crops, which has been remarkably consistent across the entire Northeast for many decades, appears to have broken down in recent years.  Whether this results from climatic changes and/or other environmental factors, and whether the cycle will self-correct or not, is unknown.  In the short term, the current scarcity of cones in montane forests appears to be benefitting BITH, which have shown relatively high recruitment of young birds during the past 3 summers, and probably will again in 2015.

VCE will be back at it again next June, so stay tuned.

Chris Rimmer checking the skull ossification  of a banded bird. / K.P. McFarland

Chris Rimmer checking the skull ossification of a banded bird. / K.P. McFarland

Loons Post Record Year for Nesting Success, Bald Eagle Nesting Down

Nesting Bald Eagle. Photo by John Hall.

Nesting Bald Eagle. Photo by John Hall.

Vermont’s loon population had a record year for nesting success, producing 65 fledglings, or chicks that survived to leave the nest, on lakes and ponds throughout the state.

Loons faced dramatic declines in the 20th century mostly due to shoreline development and human disturbance of loon habitat, but were removed from Vermont’s endangered species list in 2005 following decades of recovery efforts.

Peregrine falcons, which also were removed from Vermont’s endangered species list in 2005, saw similarly strong nesting success this year.

“Rare birds such as peregrine falcons and loons are very sensitive to human disturbance while nesting,” said John Buck, nongame bird project leader for the Fish & Wildlife Department.  “They nest only in a few specific habitats, so they need to find these in undeveloped places that are away from people.”

The lingering winter weather appears to have proven difficult for Vermont’s nesting bald eagles, which produced only 17 fledglings in 2014, down from 2013’s modern day record of 26.

“A single down year for bald eagle nesting is not a major concern at this point, as nesting success will vary from year to year due to fluctuations in weather or food,” said Buck. “We remain optimistic about the future of eagles in Vermont due to the widespread reports we have received of adult eagles throughout the state.”

Bald eagles are no longer a federally endangered species, but they are still listed under Vermont’s Endangered Species Act, as the birds have been slower to recover in the state.

Other bird species monitored by the Fish & Wildlife Department and its partners saw mixed nesting success this year. Common terns produced only 16 fledglings out of 220 nests, due in part to depredation from gulls and great-horned owls on the nests.  Biologists also monitored the grasshopper sparrow and black tern, which appeared to be stable in their small and limited habitats.

Vermont’s rare birds are monitored in a cooperative agreement between the Fish & Wildlife Department and its conservation partners, Vermont Center for Ecostudies and Audubon Vermont.

“The return of loons and peregrines to Vermont is one of the state’s great conservation success stories, but much remains to be done,” said Buck. “The continued support from our partners and from the citizens of Vermont is critical for the future success of these important species.”

Loons on WCAX and Burlington Public Access Channel 17

Loon family on Wantastiquet Pond in Weston, VT.  Photo by Joanne Bridges

Loon family on Wantastiquet Pond in Weston, VT. Photo by Joanne Bridges

The media likes a “feel-good” story and this summer they’ve picked up loons as a “good” topic.  VCE biologist and Vermont Loon Conservation Project Coordinator, Eric Hanson, was recently interviewed for a short segment on WCAX news and a long conversation (30 min.) for Burlington’s Ch. 17 Public Access TV station.  Some of VLCP loon volunteer Gail Osherenko’s video footage from Loon Chick’s First Summer is shown during the Channel 17 interview (www.LoonChicksFirstSummer.com).  To view these interviews, go to:

WCAX news spot: http://www.wcax.com/story/26439773/helping-loon-chicks-thrive-in-vt

Channel 17 / Town Meeting TV: http://www.cctv.org/watch-tv/programs/vermont-loon-conservation-project

And the story is good, mostly, with another record year in nest attempts (83 confirmed, checking on a potential 84th).  Chick productivity is down about 10% compared to previous years but Vermont is still above the national average.  The reason for the decline is due in part to competition amongst loons, which is expected to maintain a stable population.  On the negative side, we’ve had 5 adult mortalities all caused by fishing gear, including at least 3 of these from lead fishing gear.  More specifics about the summer loon season results will be coming shortly.  

Next spring, look for another story on WCAX’s and UVM’s Across the Fence Program featuring VLCP volunteers Roy Pilcher and Bob and Linda Tucker.  


A Sad Centennial

Passenger Pigeon

Passenger Pigeon

A sad 100th anniversary tomorrow. On September 1, 1914, the last passenger pigeon in the world, Martha, died in the Cincinnati Zoo; her death cemented the extinction of the passenger pigeon species, whose population numbers were once in the billions.

“The number of pigeons [at Clarendon, Vt.] was immense . . . For an hundred acres together, the ground was covered with their dung, to the dept of two inches. Their noise in the evening was extremely troublesome, and so great that the traveler could not get any sleep, where their nests were thick. About two hours after sunrise, they rose in such numbers as to darken the air.”
-William Samuel, The Natural and Civil History of Vermont, 1794.

After 90 Percent Decline, Federal Protection Sought for Monarch Butterfly

MonarchsWASHINGTON— The Center for Biological Diversity and Center for Food Safety as co-lead petitioners joined by the Xerces Society and renowned monarch scientist Dr. Lincoln Brower filed a legal petition today to the U.S. Fish and Wildlife Service seeking Endangered Species Act protection for monarch butterflies, which have declined by more than 90 percent in under 20 years. During the same period it is estimated that these once-common iconic orange and black butterflies may have lost more than 165 million acres of habitat — an area about the size of Texas — including nearly a third of their summer breeding grounds.

“Monarchs are in a deadly free fall and the threats they face are now so large in scale that Endangered Species Act protection is needed sooner rather than later, while there is still time to reverse the severe decline in the heart of their range,” said Lincoln Brower, preeminent monarch researcher and conservationist, who has been studying the species since 1954.

“We’re at risk of losing a symbolic backyard beauty that has been part of the childhood of every generation of Americans,” said Tierra Curry, a senior scientist at the Center for Biological Diversity. “The 90 percent drop in the monarch’s population is a loss so staggering that in human-population terms it would be like losing every living person in the United States except those in Florida and Ohio.”

The butterfly’s dramatic decline is being driven by the widespread planting of genetically engineered crops in the Midwest, where most monarchs are born. The vast majority of genetically engineered crops are made to be resistant to Monsanto’s Roundup herbicide, a uniquely potent killer of milkweed, the monarch caterpillar’s only food. The dramatic surge in Roundup use with Roundup Ready crops has virtually wiped out milkweed plants in midwestern corn and soybean fields.

“The widespread decline of monarchs is driven by the massive spraying of herbicides on genetically engineered crops, which has virtually eliminated monarch habitat in cropland that dominates the Midwest landscape,” said Bill Freese, a Center for Food Safety science policy analyst. “Doing what is needed to protect monarchs will also benefit pollinators and other valuable insects, and thus safeguard our food supply.”

Monarch butterflies are known for their spectacular multigenerational migration each year from Mexico to Canada and back. Found throughout the United States during summer months, in winter most monarchs from east of the Rockies converge in the mountains of central Mexico, where they form tight clusters on just a few acres of trees. Most monarchs west of the Rockies migrate to trees along the California coast to overwinter.

The population has declined from a recorded high of approximately 1 billion butterflies in the mid-1990s to only 35 million butterflies last winter, the lowest number ever recorded. The overall population shows a steep and statistically significant decline of 90 percent over 20 years. In addition to herbicide use with genetically engineered crops, monarchs are also threatened by global climate change, drought and heat waves, other pesticides, urban sprawl, and logging on their Mexican wintering grounds. Scientists have predicted that the monarch’s entire winter range in Mexico and large parts of its summer range in the states could become unsuitable due to changing temperatures and increased risk of drought, heat waves and severe storms.

Monarchs need a very large population size to be resilient to threats from severe weather events and predation. Nearly half of the overwintering population in Mexico can be eaten by bird and mammal predators in any single winter; a single winter storm in 2002 killed an estimated 500 million monarchs — 14 times the size of the entire current population.

“We need to take immediate action to protect the monarch so that it doesn’t become another tragic example of a widespread species being erased because we falsely assumed it was too common to become extinct,” said Sarina Jepsen, endangered species director at the Xerces Society. “2014 marks the 100th anniversary of the extinction of the passenger pigeon, which was once so numerous no one would ever have believed it was at risk of extinction. History demonstrates that we cannot afford to be complacent about saving the monarch.”

“The purpose of the Endangered Species Act is to protect species like the monarch, and protect them, now, before it’s too late,” said George Kimbrell, senior attorney at the Center for Food Safety. “We’ve provided FWS a legal and scientific blueprint of the urgently needed action here.”

“The monarch is the canary in the cornfield, a harbinger of environmental change that we’ve brought about on such a broad scale that many species of pollinators are now at risk if we don’t take action to protect them,” said Brower, who has published hundreds of scientific studies on monarchs.

The Fish and Wildlife Service must now issue a “90-day finding” on whether the petition warrants further review.


For an FAQ on the Monarch Butterfly Endangered Species Act Petition, please click here.


Do Non-Breeding, Single Loons Have Territories?

willoughby loon head nod carol radic 8-13

Willoughby Loon Returns. Photo by Carol Radic

Last week, Chris Rimmer and I traveled to Lake Willoughby to meet with Carol Radic and Colm Darcy, who helped me rescue a loon entangled in fishing gear back in July of 2011. I banded this bird before releasing it, and Carol and Colm have observed it every summer since. Carol “told” the loon to show up for us last week, and sure enough, it drifted by close enough for Chris to observe the color bands underwater.

Three years after we banded it, this loon continues to occupy the same section of Lake Willoughby shoreline. I would think that the bird (a probable male by size) would be seeking a breeding territory on a nearby lake with suitable nesting habitat, such as Long or May Pond. Lake Willoughby has no marshes or islands, and no known history of loon nesting. A big question for me is why this loon remains in the same area year after year? Very little is known about non-breeding loons, including where they live during the summers prior to establishing a territory. Most information comes from Dr. Walter Piper’s research following banded chicks that return as adults, and where they acquire territories. (See the 2014 Loon Caller newsletter for a story about some of Piper’s findings).

This loon obviously uses Lake Willoughby as its summer residence. The bird appears to concentrate on only one section of the lake near Carol and Colm’s camp, using it effectively like a breeding territory, but without a mate, or nesting. We’ve observed yodeling and other territorial–like behaviors on other large, non-breeding lakes, indicating that these unpaired loons are defending some kind of resource (e.g., feeding and resting areas). The banded Willoughby loon may in fact be investigating nearby breeding lakes, biding its time for an eventual takeover challenge while it uses Lake Willoughby as a secure spot to live. The availability of large lakes that lack active breeding territories may be an important resource for non-breeding loons as they prospect for mates and territories.

We may never know the answer to some of these questions, but it’s amazing to think that this individual loon keeps returning to the very spot where we rescued it. It’s irresistibly tempting to suspect that the bird might be offering a “thank you”, in its own way.

Eric Hanson, Vermont Loon Conservation Project