Category Archives: Archosaurs

9/11 Tribute in Light: bird monitoring.

You can see them from sixty miles away: twin beams of light reaching from lower Manhattan into the highest visible reaches of the sky. The beams burn through the night on September 11th, a memory, a tribute in light made from 88 7000W xenon bulbs.

Also in the New York skies in mid-September: hundreds of thousands of migrating birds. From afar, the beams look to the birds like…we don’t know…perhaps moonlight, or a gleam of sun out of place, or a streak of magnetic weirdness across the birds’ inner eye. The birds are drawn to the beams, then snared by the light. Look up from the ground and you see hundreds of circling birds. Through binoculars, the higher parts of the beams are so full of birds that the clouds of illuminated bodies look like the Milky Way in motion. Thousands of warblers, orioles, woodpeckers, and thrushes, each turned to a silvery mote.

I joined NYC Audubon to monitor and count birds at the tribute. We watched from the Battery Rooftop Garden, a terrace filled with fruit trees and vegetable beds 34 stories above the street, right next to the beams.

When the bird count got too high, the operators of the 9/11 memorial extinguished the beams for a few minutes, allowing the birds to escape from their photonic prison. Winged creatures in motion, animating the memorial beams, then released.

Looking directly up from a few blocks east of ground zero: The Tribute in Light lancing the sky. The bright spot along each beam is a thin cloud layer.

Closer to the lights, the birds are visible in each beam.

Twin beams. They’re parallel, but seem to converge high in the sky.

From the rooftop gardens on a building near One World Trade.

Counting birds in the beams. We’re 34 stories above the street.

A 1/6 second exposure: the flight path of each bird is revealed.


Major bird kill at Sewanee’s Memorial Cross

A scene of bird carnage at Sewanee’s War Memorial Cross on the campus of the University of the South (photo credits: Sandy Gilliam):


The cross is a tall white structure, brightly illuminated all night by spotlights. It stands on an overlook on the edge of the Cumberland Plateau in Tennessee, surrounded by hardwood forests, and visible from many miles away in the valley below. The night of the kill — 26/27 September — was cloudy and birds got caught in the dome of light, circling circling circling until they killed themselves by smashing into the out-sized reconstruction a Roman instrument of execution. Over 130 birds were killed.




Sora rails and American redstart


Yellow-billed cuckoos and wood thrush


Pied-billed grebes, nighthawk, and nightjar

Many bird migrate at night, avoiding predators, staying cool, and navigating by the stars. Bright electric lights disorient them and many are killed each year in collisions with communication towers, buildings, and other artificially lit structures. The numbers killed in this way are hard to know, but one recent review estimated “hundreds of millions (building and automobile collisions), tens of millions (power line collisions), millions (power line electrocutions, communication tower collisions)”.

Data from (an online database of millions of bird sightings) reveals the migration patterns of birds. The following graphs are from the “Central Hardwoods” and “Appalachian Mountains” of Tennessee (to run your own analyses, click on “explore data” at ebird). The height of the green bars on the graph indicate abundance. Each species has a different seasonal pattern (some are here only in the summer, others surge through in migratory pulses, and many are winter visitors). For many migrant songbirds, mid-September through early October are peak times for movement through our region. These migrants are often very abundant in the forests around Sewanee: every bird taking the overland route from the northern US or the the vast Canadian boreal forest is winging through the southeast.




Within a few hours of the discovery of the dead birds, staff from the University’s offices of Environmental Stewardship & Sustainability and Physical Plant Services were developing a plan to rework lighting to avoid future kills during bird migration. Many thanks to Nate Wilson, Sandy Gilliam, Greg Rollins, William Shealey, and colleagues for their rapid and proactive response.

Reminder of what flies over unseen on autumn nights

A sora, dead on the road outside the post office in Sewanee, Tennessee. These are wetland birds of the north. A dry road gutter in a town built in the southern forested uplands is a far cry from the sora’s usual marshy home.

img_20160912_133918895 This is not the first dead rail that I’ve seen on Sewanee’s roads during the autumn. Their nocturnal migratory flights carry them over the Cumberland Plateau. Perhaps they are lured then confused by the “security” lights that festoon our small downtown area. An early morning driver must have struck this bird as it wandered the road.


Those stubby wings are well adapted to movement in the dense vegetation of marshes. They’re also powerful enough to carry the birds — those that escape our lights and tires — over the Gulf of Mexico to their wintering grounds in Central and South America.

Listen as you walk in the evening: autumnal migrants are streaming through the skies every night, calling as they fly. Chirp, tzup, zzip, the sound of hundreds of thousands of memories of wetland, forest, and prairie, winging bird-thoughts south, away from the leading edge of winter. We’re hearing part of the landscape’s mind in motion. On the roads, in the morning, tiny flecks of lost understanding.



Mastery through simplicity: Tide pool springtails, Anurida maritima

Anurida maritima

As if the tide pool surface was ice, hundreds of small gray animals skate and jiggle over the salt water. Not a single one of the animals is wet. None sink. In gusty wind their swarms blow back and forth within the confines of the rocks that wall the tide pools. In still air, the animals’ tremulous movement draws them into ever-shifting amoeboid shapes.

Anurida maritima, the “seashore springtail,” has a distribution that encompasses most of the rocky shores of the North Atlantic. This species’ daily rhythms are tuned to the tides. At low tide, the springtails disperse over the exposed rocks, scavenging for food (including discards from mollusc-throwing gulls, as I discovered a few weeks ago). About an hour before the rising tide submerges them, the springtails retreat to rocky crevices and huddle. When the tide reaches its full height, the animals are fully submerged. This rhythm seems to be controlled from within: they keep up the cycle of activity tuned to the tides even when removed to a lab.

Not many animals can be so amphibious. Oxygen, in particular, is hard to come by. Land animals have lungs adapted to air, sea creatures have gills that can extract oxygen from water. There is not much room for an “in between” state. Animals with lungs hold their breath underwater, then surface to gasp more oxygen. Marine animals exposed at low tide close their shells and trap doors to keep their gills moist. Springtails manage to break these rules and thrive by adopting the path of simplicity. Oxygen enters their bodies across their skin, so during high tide they wander in the open air without lungs. When submerged, the waterproof hairs on their bodies hold a layer of air close to the skin, like a diver’s air tank.

The springtails use more than their body hairs, though, to carry them through 3-4 hours of submergence at high tide. They seek out rocks whose undersurfaces allow several springtails to huddle within an air bubble. If they’re lucky (and clever) enough to find a good spot, the bubble keeps the animals oxygenated through the entire high tide cycle, acting like a lung into which oxygen diffuses from the sea water. By the end of the tidal cycle the bubble is depleted — it shrinks and eventually disappears — and the animals must tolerate low oxygen for a while. Then, when the waters recede, they are free to wander the wrack and see what washed up on the falling tide.

Relatively simple though this strategy may be, it is extraordinarily successful. Close inspection of rocks reveals the springtails wandering nearly every surface at high tide. There seem to be thousands of them in a single square meter. These close relatives of the insects may lack wings, internal breathing apparatus, and elaborate body appendages, but lack of anatomical sophistication has unlocked feeding and living opportunities for which no other creature seems able to compete.

Anurida maritima 2


Cold, cold bathing (duckling style)

The Labrador Current carries water from northern Greenland down the Canadian coast, then swirls its iciness into the Gulf of Maine. On the Maine shore, waiting for the splash, are common eider ducklings:






whee that was fun, can we go swim now?

In the surf, the downy balls have no trouble. As a breaker approaches, they dive then pop back to the surface, paddling in the sea spume and froth.


When they hatch the ducklings weigh just 70 grams. After ten weeks of growth those that have not been eaten by gulls and seals are nearly as heavy as adults, about 1600 grams. They accomplish all this while keeping their bodies at 40°C (104°F) despite the frigid water (10°C, 50°F on a good day in the early summer). Their diet must therefore be rich in protein and fat — crustaceans, and other sea animals — and their eiderdown coats tight.

Small avian endotherms have no trouble with the water. Surely I should take a dip and join them?


I lasted a screamingly cold two minutes. The first minute was pure pain, the second was alarmingly numb. I salute you, eider ducklings.

These eiders in Maine live at the southern edge of a range that encompasses much of the northern coastline around North America and Eurasia. The species is listed as “near threatened” meaning that we have significant cause for concern about its future.

Locally, here in Maine, the situation was dire but has improved. Bradford Allen‘s review of eider biology in Maine reports that over-hunting in the late 19th and early 20th centuries reduced the population from tens or hundreds of thousands of birds to just four birds nesting on one sea island. At the time, many of Maine’s coastal islands were inhabited by people; nesting birds fared very poorly alongside hungry human settlers. By 2000, after several decades of hunting restrictions and the abandonment of Maine islands to well-fed tourists, the population had risen to 29,000 pairs nesting on over 300 islands.

Across North America, population trends are mostly unknown. Hunting continues. According to the Sea Duck Joint Venture, a collaboration among scientific and management groups:

Within North America, most sport harvest occurs along the Atlantic coast; with about 15,000 birds taken in Canada and about 23,000 in the New England states. They continue to be harvested commercially (80,000+ birds/yr) in Greenland, and this may not be sustainable.

BirdLife International reports that:

In Europe the population size is currently declining overall at a rate of >40% over three generations…Given the strong declines in the European population and a lack of compensatory increases in the North American population the overall population trend is thought to be declining moderately rapidly.

So although eider populations have rebounded from the edge of extinction in some parts of coastal Maine, their longer term future is uncertain. Current threats include oil spills, entanglement in nets, over-hunting, disturbance from expanding industrial activity, poisoning from mercury and other pollutants, predation by gulls and eagles, and nesting site disruption by development and tourism.

Maine’s history of near annihilation followed by recovery gives us reason for hope. If we can stay out of their way, young eiders will continue their 28 million year history of salt-water life.




Grassland birds

In a hay meadow near Brunswick, Maine:

Bobolink, taking a break from his jumbled singing flights over the field.


Savannah sparrow, keeping an eye on neighboring males.

sav sp1

According to the North American Breeding Bird Survey, neither species has been faring well. The bobolink has declined by about 2% per year since the 1960s. The savannah sparrow’s decline is about 1.25% per year.

North American Breeding Bird Survey trend for bobolink, then savannah sparrow (“index” on the vertical axis is a measure of the number of birds seen along annual survey routes):

boblink suvey wide

sav graph surveywide

These declines are typical for meadow species in North America. According to a review by ornithologist Jon McCracken, birds that nest in upland grasslands have, in the last century, “experienced the most pronounced declines of any other group of birds on the North American continent.”

In the last few decades, intensification of agriculture — earlier hay-cutting, more frequent hay-cutting, conversion of grass to alfalfa — has drastically reduced breeding success of these species. Before that, in the mid-1900s, regrowth of forests on former agricultural land was the main cause of the decline of grassland birds. This followed the 1800s and early 1900s, the heyday of hay in eastern North America. Early European colonists cleared large areas of forest, opening grassland. Then, as American agriculture moved to the midwest and heating oils replaced firewood, grasslands in eastern North America declined as forests regrew (and grasslands in the midwest declined as they were plowed for grain crops).

Given the great variability of grassland acreage over the last centuries, the “right” or desirable amount of bird-friendly grassland in the region is obviously hard to state. But the combined effects of early hay cutting (goodbye nests) and land conversion (hello alfalfa fields and housing subdivisions) suggests that, if we want to maintain populations of these species, we’ll need more (and better) grassland than we now have. The economics of farming makes this a significant challenge. Stiff competition from industrialized meat and milk businesses mean that hay meadows are not money-makers, hence the long-term decline.

sav sp flight




Continental gyre of birds.

A paper published this week by scientists at the Cornell Lab of Ornithology uses eBird data to map the migratory paths of birds in the Western Hemisphere. eBird is a free online checklist program used by tens of thousands of bird watchers. The database now has millions of observations from across the world, most of them in North America. This latest study used 6.1 million eBird checklists to find the “center” of bird species’ ranges through the year. The summary below shows, for 118 species, how these centers move. Each point is one species, tracked through checklists over a year.

bird map

A pattern emerges: birds tend to “loop” clockwise, migrating north in the spring overland through Central America and Mexico, then flying south in the autumn over the Gulf of Mexico and the Atlantic. These loops are caused by prevailing winds, especially the northeast trade winds over the ocean. Turn, turn, turn: sung by the Byrds.

To my eye, deviations from the pattern are just as fascinating. Why do some species veer so far east? Why do some linger in the south, then zip north in a rush? A map with each dot labelled by species lets us peer into these mysteries.

To write honestly and with conviction anything about the migration of birds, one should oneself have migrated. Somehow or other we should dehumanize ourselves, feel the feel of feathers on our body and wind in our wings, and finally know what it is to leave abundance and safety and daylight and yield to a compelling instinct, age-old, seeming at the time quite devoid of reason and object.” — William Beebe