Mass Audubon’s Arcadia Wildlife Sanctuary: a few miles from where Emily Dickinson was inspired by Bobolinks- which have returned to the property thanks to careful stewardship.

References to Bobolinks abound in poetry from 19th-century New England. Massachusetts authors drew inspiration from local birds for a host of reasons, not least because they saw local species as uniquely American subjects (as opposed to, say, the European Nightingale). Bobolinks and Meadowlarks helped distinguish their work from other English-language poets’, and perhaps more importantly, ground it in a sense of place.

Bobolinks were also particularly an familiar and evocative sight through the 1800s and into the past century. Widespread low-impact agriculture provided habitat for field-loving Bobolinks, which don’t mind living near humans as long as their nests are undisturbed. Conspicuous and bold, Bobolinks became an icon of the countryside, and a cultural touchstone for many.

Emily Dickinson, one of rural Massachusetts most-celebrated poets, took a particular liking to them. Bobolinks recurred as a motif in more than 20 of her works. Dickinson often made the birds into rowdy or joyfully anti-authoritarian figures, as here:

 

Some keep the Sabbath going to Church –
I keep it, staying at Home –
With a Bobolink for a Chorister –
And an Orchard, for a Dome –

Some keep the Sabbath in Surplice –
I, just wear my Wings –
And instead of tolling the Bell, for Church,
Our little Sexton – sings.

God preaches, a noted Clergyman –
And the sermon is never long,
So instead of getting to Heaven, at last –
I’m going, all along.

–Emily Dickinson

 

Loosely interpreted, the poem emphasizes finding joy in nature and in the everyday. Here, the Bobolink is part of Dickinson’s everyday “Heaven” on earth; its song part of her quiet resistance to organized religion. Dickinson had studied religion in a seminary, but perhaps tellingly, dropped out after a year.

Dickinson always ascribes human qualities to the bird to illustrate a point—whether as a “Sexton” (someone who rings the bells of a church) calling her attention to beauty in nature, or in other poems, as a disruptive “Rowdy of the Meadow.”

Other poets, however, grounded poems in Bobolinks’ natural history and biology, although few connected them with complex societal themes as adroitly as Dickinson. William Cullen Bryant, for example, managed to accurately convey key points about Bobolinks’ seasonal behavior (despite leaning pretty heavily on twee personification and cutesy metaphors):

 

Merrily swinging on briar and weed,
Near to the nest of his little dame,
Over the mountain-side or mead,
Robert of Lincoln is telling his name:
Bob-o’-link, bob-o’-link,
Spink, spank, spink;
Snug and safe is that nest of ours,
Hidden among the summer flowers;
Chee, chee, chee.

Robert of Lincoln is gaily drest,
Wearing a bright black wedding-coat;
White are his shoulders, and white his crest;
Hear him call in his merry note:
Bob-o’-link, bob-o’-link,
Spink, spank, spink;
Look what a nice new coat is mine,
Sure there was never a bird so fine.
Chee, chee, chee.

Robert of Lincoln’s Quaker wife,
Pretty and quiet, with plain brown wings,
Passing at home a patient life,
Broods in the grass while her husband sings:
Bob-o’-link, bob-o’-link,
Spink, spank, spink;
Brood, kind creature; you need not fear
Thieves and robbers while I am here.
Chee, chee, chee.

Modest and shy as a nun is she;
One weak chirp is her only note,
Braggart and prince of braggarts is he,
Pouring boasts from his little throat:
Bob-o’-link, bob-o’-link,
Spink, spank, spink;
Never was I afraid of man;
Catch me cowardly knaves, if you can !
Chee, chee, chee.

Six white eggs on a bed of hay,
Flecked with purple, a pretty sight!
There as the mother sits all day,
Robert is singing with all his might:
Bob-o’-link, bob-o’-link,
Spink, spank, spink;
Nice good wife, that never goes out,
Keeping house while I frolic about.
Chee, chee, chee.

Soon as the little ones chip the shell,
Six wide mouths are open for food;
Robert of Lincoln bestirs him well,
Gathering seeds for the hungry brood.
Bob-o’-link, bob-o’-link,
Spink, spank, spink;
This new life is likely to be
Hard for a gay young fellow like me.
Chee, chee, chee.

Robert of Lincoln at length is made
Sober with work, and silent with care;
Off is his holiday garment laid,
Half forgotten that merry air:
Bob-o’-link, bob-o’-link,
Spink, spank, spink;
Nobody knows but my mate and I
Where our nest and our nestlings lie.
Chee, chee, chee.

Summer wanes; the children are grown;
Fun and frolic no more he knows;
Robert of Lincoln’s a humdrum crone;
Off he flies, and we sing as he goes :
“Bob-o’-link, bob-o’-link,
Spink, spank, spink;
When you can pipe that merry old strain,
Robert of Lincoln, come back again.
Chee, chee, chee.

– William Cullen Bryant

 

Bryant’s poem draws a parallel between the Bobolink’s behavioral changes over a breeding season and a human who is burdened with work and worry as they age. But the poem is essentially fanciful, and its goal is mainly to describe these seasonal arcs with flowery language. Still, it’s a rare poem for weaving in a significant amount of natural history.

One could say that Dickinson’s and Bryant’s poems have different goals. Dickinson uses the Bobolink as a device to illustrate the experience of finding joy and religion in nature; she ascribes human qualities to a bird to tell us something about ourselves. Bryant’s poem ascribes human qualities to a bird, but more to illustrate points about the bird itself.

Which poem do you prefer? Do you know of any contemporary poems about Bobolinks—or maybe have written one yourself? Share with us below in the comments!

You can also learn more about (currently-living) Bobolinks and how to protect them at Mass Audubon’s Bobolink Project website.

 

Tips For August Nighthawk-Spotting

Aerobats. Daredevils. Show-offs. The bounding, athletic flight the Common Nighthawk makes for an impressive spectacle in late summer twilight, when groups of these birds swoop to catch insects in midflight.

In the last two weeks of August into early September, these birds power across Massachusetts on hooked, falconlike wings. Nighthawks pause during migration to gather and feed near the edges of open fields, making them easy to observe on their way South.

Two Common Nighthawks streak through the sunset light in Cambridge, MA. Composite image by Will Freedberg.

Nighthawks are totally unrelated to hawks, a group with which they share very little. As members of the nightjar family, nighthawks look similar to the closely-related Whip-poor-will when perched on the ground. In the air, they appear totally unique, agilely swooping and diving in continuous flight.

While springtime brings modest numbers of nighthawks to New England, they show up in much greater numbers on their southbound migration. Nighthawks feed on flying ants, which hatch here en masse in late summer, to fatten up before making the long trip to South America. In spring, when insects are scarce, most nighthawks take a more direct route around Massachusetts to their breeding grounds.

Don’t miss the three-week window for seeing migrating nighthawks this year! Here are some tips for finding them.

 

Find a Field

Just before sunset, nighthawks often emerge around grasslands and big fields. Near Boston, nighthawk hotspots include Millennium Park in West Roxbury, Rock Meadow in Belmont, and Heard Conservation Land in Wayland. In the rest of the state, any open hilltop or good vantage point near a river will do!

 

Follow the Rivers

Nighthawks use river valleys to navigate. While any open field is apt to produce a nighthawk sighting at dusk in late August, rivers running North-South tend to concentrate nighthawks in impressive numbers. In the Connecticut River Valley, this can mean over a thousand birds streaming by over the course of the evening—although such a spectacle doesn’t happen every year.

 

Join a Program

Mass Audubon sanctuaries host nighthawk searches in every part of the state! Here are a few that are coming up:

 

Connecticut River Valley
August 22, 2018

Nighthawks and Chimney Swifts at Arcadia Wildlife Sanctuary

This program will begin with an indoor presentation about each bird before heading out to search the sky for nighthawks and swifts.

 

Western Massachusetts
August 24, 2018

Evening Nighthawk Watch at Canoe Meadows

Search the evening sky for migrating nighthawks at Canoe Meadows. With luck, you’ll be able to observe these beautiful aerial acrobats catching insects on the wing. This event is free.

 

Worcester Area
August 28, 2018:

Migration of the Common Nighthawk in Millbury

Learn about nighthawk adaptations, ecology, and how to look for feeding behavior, while witnessing their migration flight.

 

Boston Area
September 5, 2018:

Sudbury River Nighthawks with Drumlin Farm

Open vistas along the Sudbury River offer perfect vantage points from which to scan the sky for nighthawks. The group will explore the marsh, grassland and orchards for other fall migrants.

 

 

Conservation Success Stories: The Osprey

Ospreys are on the rebound after a troubled past. Despite a history of pesticide poisoning, persecution, and population declines, Ospreys have returned as one of the most abundant raptors of the coast. Today, the Osprey’s story stands as a testimony to the power of scientifically-informed environmental activism.

An Osprey stands watchfully on a snag over a marsh. Photo © William Freedberg 2015

DDT: A Silent Threat

Osprey numbers crashed dramatically following the widespread use of DDT, a pesticide deployed across America in the 1940s. While previous decades saw Ospreys hunted as “pests” and their wetland habitats drained for development, the introduction of DDT all but rang the death knell for the entire US Osprey population.

Nobody realized it at the time, but DDT builds up in animals’ body tissue, and persists in the environment years after being sprayed on farm fields. This spelled trouble for birds of prey: while DDT spraying rarely poisons adult birds to death, it destroys the structure of raptors’ eggshells, preventing them from reproducing.

As a result, Ospreys declined by over 90% between 1950 and 1970. When the now-famous environmentalist Rachel Carson finally named DDT as the culprit in her book Silent Spring, the discovery ignited a movement. A coalition of the National and Massachusetts Audubon societies, as well as local land trusts and nationwide advocacy groups, intervened on behalf of all species threatened by DDT. They sued the Environmental Protection Agency to ban the pesticide—and won.

A few decades later, Ospreys are almost back to their pre-DDT abundance.

 

A Place To Nest
 The DDT ban eliminated a significant threat to Ospreys, but the bird didn’t immediately bounce back. Even in places with clean water and plenty of fish, Osprey numbers are naturally limited by the number of appropriate nest sites. They normally require a tall, dead tree at the edge of a marsh, but lacking standing trees in the open, they settle for utility poles or other problematic locations.

Artificial nest platforms are one solution. In addition to keeping Osprey nests away from telephone wires and buildings, nest platforms increase the number of Ospreys any wetland can support. With wetland edge habitats constantly losing ground to development, it’s critical to maximize the number of Osprey nesting in appropriate wetlands.

 

Mass Audubon Continues To Support Ospreys

Mass Audubon’s South Shore Osprey Project maintains about 100 Osprey nest platforms. The project also monitors and records data on the Osprey population, including banding and tagging several birds, and tracking their movements. The data never fails to yield exciting results— whether demonstrating Ospreys’ reliance on the spring herring migration for food, or revealing variability in Ospreys’ choice of wintering grounds (South Shore birds end up in places as far away from one another as Cuba and Bolivia).

If you love Ospreys as much as we do, consider sponsoring a nest platform!

The Ten Craziest Massachusetts Bird Noises

If you’ve never heard a male Snowy Egret nasally bubble away at a rival, well, you are in for a treat.

Using Xeno-canto, an online library of bird sounds to which anyone can contribute, we’ve chased down the strangest recordings of species native to Massachusetts. Hit the play button in the clips below to check them out!

In the first half of this post, we’ll run through some strange bird noises that are easy to go out and hear for yourself.

We’ll review even weirder noises in the second half, but ones that are hard or impossible to experience in Massachusetts. This second section is devoted to noises that migratory birds make on their breeding grounds far to the north, or in other parts of their range.

Part 1: Sounds You Can Hear in Massachusetts

1. American Bittern:

Distant relatives of herons, bitterns make a booming, gulping noise while pumping their necks up and down, giving them the nickname “thunder-pumper.” Hit the play button in this clip and turn up the bass!

An American Bittern stands tall among marsh grasses. Photo (c) William Freedberg

2. Bobolink:

A once-common sound of farm fields and grasslands, the Bobolink’s song incongruously brings to mind R2-D2 from Star Wars.  These grassland birds abounded during the height of low-impact agriculture in New England, but farmland loss, development, intensive harvesting and pesticide use have reduced their numbers dramatically.  With recent conservation programs like the Bobolink Project, which pays farmers directly to protect grassland birds, this species’ future is looking a little brighter.

 

3. Veery:

Veeries are drab, russet-colored thrushes with an outsized voice. They can produce several clear tones at once, and almost sound like they are harmonizing with themselves. While uncommon near developed areas, this birds are one of the most numerous summer birds of deep forest far from the coast.

 

4. Barred Owl:

Owls don’t just hoot—they also can yelp, screech, and shriek. This Barred Owl transitions from a high-pitched wail (which may be a regionalism or an alarm call) into its lower and more commonly-heard “who-cooks-for-you-all.”

 

5. Common Loon:

Perhaps the most iconic sound on this list, the wail of the Common Loon is practically synonymous with the wilderness of northern New England (although they also breed in central Massachusetts). In this recording, listen for their yodels at the beginning, a loud wail at 0:31, and keening starting at 0:09 and 0:58.

Part 2: Sounds Massachusetts Birds Make Elsewhere

6. Snowy Egret:

This might be the weirdest one on the list. Graceful Snowy Egrets are common in New England saltmarshes, but rarely vocalize away from rookeries. At rookeries, however, they’re known for a cartoon character-like and downright hilarious.

A Snowy Egret patrolling the shallows for prey. Photo (c) William Freedberg

7. Pectoral Sandpiper:

Pectoral Sandpipers and many other species of shorebirds seem like much different animals on their breeding grounds than on the east coast during migration: they become quite fearless and territorial, their plumage takes on dramatic patterns, and they sing with a surprising variety of chortles, whoops and whistles. This Pectoral Sandpiper’s song sort of sounds like… somebody blowing bubbles?

 

8. Turkey Vulture:

Turkey Vultures almost never vocalize. When they do, all that comes out is a raspy, sizzling hiss, like adding water to a hot pan.

 

9. Atlantic Puffin:

While puffins are uncommon winter visitors to the waters off MA, you can easily hear their characteristic grumbles on breeding colonies in Maine.

 

10: Great Shearwater:

These pelagic, albatross-like birds are frequently encountered on whale watches and offshore boat trips in Massachusetts waters. While silent at sea, they’re… really quite vocal on breeding colonies, where they sound like rubber chickens brought to life.

A Great Shearwater, true to its name, glides tight to the waves. Photo (c) William Freedberg

These are just our picks for the strangest noises made by local birds… but there are so many other options, it’s hard to winnow them down to just a few!

What would make your top ten? Let us know in the comments! 

 

 

 

Bird Conservation on the Road in Iceland

Hrisey Island © Margo Servison

From June 12–21 two members of the Bird Conservation team, Jon Atwood and Margo Servison, were privileged to visit Iceland with a Mass Audubon Natural History Tour. Along with 14 other travelers, we saw incredible geology, waterfalls, geysers, flowers, sea cliffs, and landscapes that can only be described as ‘otherworldly’. Oh, and lots of birds—74 species, the majority of which are seldom seen in North America, and nearly all of which were seen by all trip participants.

European Golden-Plover © Margo Servison

It was an amazing experience, to be in a world where the dominant bird species were shorebirds, waterfowl, and seabirds—there were only about 10 species of songbirds. Black-tailed Godwits, Red-necked Phalaropes, Gyrfalcon (even including a nest with 3 chicks), Atlantic Puffin, and European Golden-Plover were the trip favorites. And our super-fabulous local tour guide (Trausti Gunnarsson), one of those people who knows everything about everything, made the trip far more than simply a great birding experience.

Red-necked Phalarope © Margo Servison

To join Mass Audubon on two NEW Iceland birding tours next year, watch this website.

 

Wildlife and Birding in Yellowstone and Grand Teton National Parks

© David Parish

While it’s true that Mass Audubon regularly sponsors outstanding wildlife and birding trips to exotic corners of the planet, the Natural History Travel Program also features domestic departures that rival some of the finest wildlife spectacles on the planet.  One of these is the Greater Yellowstone Ecosystem—a region covering approximately 34,375 square miles in the northwestern corner of Wyoming, but also extending into Idaho and Montana.  Comprised of more than 2.2 million acres, this scenically magnificent region with an elevation averaging over 7500’ hosts the largest concentration of wildlife in the United States outside of Alaska, including the largest free-ranging herd of American Bison in the world, one of the largest American Elk herds in North America, and one of very few Grizzly Bear populations in the contiguous United States.  And thanks to a repatriation effort in the mid-1990s, Yellowstone supports 11 packs of Gray Wolves numbering approximately 110 individuals.

Bison © David Parish

From June 12-22, Mass Audubon President, Gary Clayton and Important Bird Areas Director, Wayne Petersen were able to share 21 species of mammals and 133 species of birds with an appreciative and congenial group of colleagues and clients in this extravagantly beautiful region.  Among the trip’s highlights was a wolf pack trying (in vain) to take down a young Pronghorn, baby bison practically at every turn, a Golden Eagle at its nest, a Dipper feeding and teaching a young one how to swim and dive, a fine variety of waterfowl including several pairs of rare Trumpeter Swans, and hosts of colorful wildflowers.  In addition, the food was hearty and fine throughout, the weather was variable but comfortable, and canoodling Grizzly Bears and Moose and Black Bears with young were consistently voted as favorites.  One of the most intact temperate zone ecosystems in the world, the Yellowstone is a region like few others and is destination that every American should see at least once in their life!

Pronghorn © David Parish

Field Notes from the Quabbin: Moose Mamas and Magnolia Warblers

A Magnolia Warbler perches in a shrub. Photo by William Freedberg

A late-June morning at the Quabbin Reservoir:  Winter Wren songs echo from hollows and wetland thickets. Blackburnian Warblers whisper their buzzy, quiet notes from the canopy. Blue-headed Vireos squeak and argue over perches in spruce trees. These birds, like many species that prefer conifers or highland forests, are rarely seen outside of migration in eastern Massachusetts. At the Quabbin, it’s hard to miss them.

In the background there’s a constant clamor from the Quabbin’s most vocal and abundant woodland breeders: Red-eyed Vireos, Veeries, Ovenbirds, and Scarlet Tanagers.

Amid the birdsong, there’s the faint scratching of my pencil and clipboard. Point 4, Minute 1 // Scarlet Tanager. Male. Calling. 19 meters // Ovenbird. Unknown sex. Singing. 33 meters.  The birds are a thick during dawn chorus, and between recording each species, sex, behavior, and distance from me, it’s hard to keep up. The survey period passes quickly, and it’s time to hike to the next count site.

The data we collected that morning will eventually be used by the National Ecological Observatory Network (NEON), an organization which studies large-scale environmental change at over 70 sites across the US, and which partners with Mass Audubon to collect bird data in New England. Normally, it takes just one person to run bird surveys—but recent security concerns at the Quabbin mean that all field technicians are now accompanied by a NEON escort to drive around restricted-access roads.

My field escort that day was Jamie, a soft-spoken botanist who had just moved to New England from Appalachia. When he mentioned he hoped to see his first moose in the Quabbin, I thought it was a farfetched idea, not knowing that around 100 moose make their year-round homes there. As if to prove a point, a cow moose stepped into the road later that day as we were on our way out.

A blurry, through-the-windshield photo of the moose that wouldn’t move.

We paused before inching the car towards the moose. The moose paused, too, and took several deliberate paces towards us. We noticed a smaller second pair of ears protruding from the roadside vegetation, and realized the moose was putting itself between us and its calf. That was our cue to put the car in reverse and give it some room; we would have to wait it out if we wanted to get to our destination safely.

Rolling down the windows, we were surprised to hear a singing Magnolia Warbler, a rare breeder for Central Massachusetts. The banana-yellow male flew across the road, giving us excellent looks at his black mask and bold stripes. I broke out a granola bar and Jamie unwrapped his lunch as we watched the moose feed and listened to the warblers. The mammoth ungulate in our way eventually ambled off, but we were in no rush to leave: life at the Quabbin was good.

America’s Biggest Ecological Monitoring Project

This summer, I’ve been surveying birds at the Quabbin Reservoir for Mass Audubon and NEON, the National Ecological Observatory Network. The deep forests and hollows of the Quabbin watershed host scarce breeders like Cerulean and Canada Warbler, along with most common woodland breeders in the state. The Quabbin’s size and diversity of intact habitats make it an ideal study site for a program like NEON.

NEON is an exciting project because of its scale. Funded by the National Science Foundation, the network comprises more than 80 sites across the country’s 20 ecoregions. At each site, NEON coordinates teams of scientists to keep tabs on a variety of ecological indicators. These include large-scale factors like water chemistry, greenhouse gasses, and tree cover, as well as narrower topics like fish DNA, bird diversity, and disease prevalence in ticks, mice and mosquitoes.

A Scarlet Tanager with insect prey, perched on a snag by the Quabbin. Photo by Will Freedberg.

 

NEON treats birds as one piece of a vast puzzle: by studying how long-term ecological trends line up with each other, the project aims to parse out the causes and consequences of environmental change.

Most importantly, all NEON data is free and publicly available. It’s fun to browse if you’re curious about any of these topics, but scientists can also leverage these massive datasets to answer specific questions about ecosystem function.

 

Strategies For Bird Surveys

Mass Audubon has been responsible for NEON’s bird data in New England since the project’s inception. Each year, we send observers (called “field technicians”) to monitor bird numbers and diversity at the Quabbin, as well as Bartlett Forest in New Hampshire.

A diagram showing the layout of bird survey points in a NEON grid. Adapted from Thibault (2015)

Technicians are responsible for surveying a number of randomly selected patches of forest, which are each divided into 3×3 grids of survey points. By standing in one place and counting birds at each evenly spaced point in a grid, the technicians minimize double-counting birds, and get a representative subsample of birds present in each grid.

Even skilled birders won’t detect every bird at a point. To get around this, NEON scientists adjust bird count data with models that account for birds that were present, but undetected by the observer.

Observers are also less likely to detect birds that are far away from them, and more likely to notice birds that are close by. So, field technicians record their distance from each bird with a rangefinder; distant birds are given more “weight” in the model for calculating actual bird abundance. This is based on the assumption that the technician recorded most nearby birds, but missed more that were further away.

Next week, I’ll be posting some entries from my field notebook, and a typical day in the life of a Mass Audubon/NEON bird technician. Stay tuned for some stories from the field.

The Warbler Connection: Bay-breasts and Budworms

Bay-breasted Warbler © Ian Davies

Massachusetts birders this spring were thrilled by the exceptional numbers of Bay-breasted Warblers present during the May migration. Joining these inflated Bay-breast numbers were also above average numbers of Cape May and Tennessee warblers.  Was this a coincidence? Probably not.  The key to their local abundance this spring probably lies in the fact that these boreal forest breeders are “spruce budworm specialists”.

The spruce budworm (Choristoneura fumiferana) is a small boreal forest moth whose larvae periodically undergo population explosions capable of destroying huge acreages of spruce/fir forest in Canada and beyond.  Under normal circumstances, boreal forest breeding birds such as the “spruce budworm specialists” mentioned above, are major predators of spruce budworm caterpillars.  When budworm populations periodically get out of control, the numbers of these budworm-eating warblers increase substantially wherever the irruption is taking place.  When a superabundance of food exists, the warblers lay more eggs and successfully raise more young than in normal years, and often do so for several years in succession, or as long as the budworm outbreak persists.

Spruce Budworm © Jerald E. Dewey, USDA Forest Service

These “boom and bust” population cycles are similar to what periodically happens to lemmings in the Arctic, or to certain species of forage fish in the ocean (e.g., sand lance or menhaden).  When these overabundances of food exist, certain predators are capable of maximizing either their reproductive output or their local abundance.  Often the phenomenon causing a detectable local abundance is far removed from the actual cause of the event.  Classic examples detectable in the Bay State are the recent major Snowy Owl irruptions of the winters of 2013-14 and 2017-18, and the menhaden/Great Shearwater event in Provincetown during the late summer of 2017.  In the case of Snowy Owls, the lemming events responsible for the Snowy Owl irruptions into Massachusetts were far north in the Arctic, not locally in Massachusetts.  However in the instance of the menhaden event, the factors leading to the Provincetown disaster were far more local and took place in Massachusetts’ nearshore waters.

To put the Bay-breasted Warbler event into an extravagant perspective, consider a third event that took place on May 28, 2018, on the north shore of the Saint Lawrence River near Tadoussac, Quebec.  On this date six highly experienced observers tallied an estimated 144,324 Bay-breasted Warblers, 108,243 Cape May Warblers, and 72,162 Tennessee Warblers in nine hours!  Partly responsible for these unprecedented and extraordinary one-day totals was a combination of weather events that created a “perfect migration storm”—the full details of which lie beyond the bounds of the current story.

Cape May Warbler © Ian Davies

More to the point, however, these massive and unprecedented numbers of “spruce budworm specialists” were part of what are almost certainly inflated populations of these species bound for budworm-besieged areas of boreal forest.  What Massachusetts observers enjoyed this spring was clearly only a tip of a much larger iceberg whose full extent has likely been building slowly for several past breeding seasons but wasn’t fully revealed until May 28 at Tadoussac, Quebec!

Part II: Chemical Clues Help Track Migratory Birds

 

Last week, we posted an article discussing how isotope ratios in a bird’s body vary depending on its past diet and geographic location. Archived in blood and hard tissue, isotopes leave a chemical record of a birds’ life history.

 

A Golden-winged Warbler on its breeding grounds in New York. Thanks to hydrogen isotope studies, we know this bird likely winters in northern Colombia. (Photo © Will Freedberg)

 

Isotope analysis has enabled a number of important discoveries about bird biology, including the following:

 

American Redstarts’ Summertime Breeding Success Depends On Winter Habitat Quality

American Redstarts feed most successfully in wet habitats, although they tolerate and occupy dry habitats as well. A team of Canadian scientists examined redstarts with varying degrees of breeding success, and used carbon isotopes to determine if there was a relationship between a redstart’s wintering grounds and the number of offspring it raised on its breeding grounds.

The ratio of Carbon to its lighter isotope, 13C, varies between wetlands and uplands because of plant metabolism: plants metabolize carbon in one of three ways, and the one most prevalent in wetland plants requires that they store more 13C. This extra 13C accumulates in the bodies of insects that feed on plants, and eventually in the redstarts that feed on insects.

The Canadian team previously showed that redstarts in wet winter habitats had more 13C in their blood cells, enabling them to identify birds on the breeding grounds that had overwintered in wet habitats. The scientists tested birds on the breeding grounds, finding that redstarts that raised more offspring in the summer also had higher concentrations of 13C in their blood, showing that they had occupied better-quality winter habitat.

By showing that wet habitats will do more for redstarts’ reproductive success than dry habitats, this study helps conservationists set priorities for protecting their wintering habitat.  More broadly, this study underscores that not all winter habitat provides what birds need to thrive during the breeding season.

 

Hydrogen Isotopes Trace Golden-Winged Warblers To Wintering Grounds

 Just as carbon isotopes show if a bird has recently occupied wet or dry areas, hydrogen isotopes help approximate the latitude and elevation of a migrating bird’s origin. A heavy hydrogen isotope, deuterium, occurs in different concentrations depending on climate and weather patterns; its extra mass means it requires more energy than regular hydrogen to evaporate. So, deuterium concentrations in water vary consistently with latitude and elevation, and as birds drink and feed, their bodies build up deuterium concentrations according to their geographic location. This map shows different concentrations of deuterium collected from songbirds across the US:

 

Adapted from Hobson and Wassenaar (1996). © Springer-Verlag Berlin Heidelberg 1996

Researchers used these patterns to determine if Golden-winged Warblers that bred in similar areas in the US stuck together on their wintering grounds. The Golden-wings’ closest relative, the Blue-winged Warbler, doesn’t do this at all—a bird from Ohio is just as likely to overwinter in Honduras as it is to end up in Mexico. But certain breeding populations of Golden-winged Warbler are in much steeper decline than others, and researchers wondered if it could be because of trouble on their wintering grounds. Deuterium analyses showed that Golden-winged Warblers follow strict migratory routes: birds in Venezuela came almost exclusively from the declining population in the southern Appalachians, while birds in Central America came from the more secure Great Lakes population. These findings suggested that regional differences in population trends might be due to specific threats along migratory routes or on wintering grounds.

 

Nitrogen Isotopes Reveal Changes In Whip-Poor-Will Diet

A study of nitrogen isotopes In Whip-poor-wills showed that the quality of Whip-poor-wills’ diet has diminished over time, contributing to their decline. A heavy nitrogen isotope, 15N, increases 2-4% with every step in the food chain. As predators consume more prey items, they excrete lighter isotopes and accumulate 15N in their bodies. So, if a Whip-poor-will eats mostly large, predaceous insects, it accumulates 15N faster than a Whip-poor-will eating mostly herbivorous insects—which also tend to be less protein-rich and less nutritious. By analyzing the 15N:14N ratio in the feathers and claws of Whip-poor-will specimens in natural history museums, ornithologists found that the quality of their diet has indeed declined through the past few decades. This study was widely popularized in the news in addition to scientific journals.