Author Archives: William Freedberg

About William Freedberg

Studies indicate that Will Freedberg occupies the ecological niche of a semi-nocturnal generalist. His habits change seasonally, doing fieldwork and bird surveys in the summer, but also blogging, coordinating volunteers, taking photos, and doing background research. Life history traits include growing up in Boston and reluctantly graduating from Yale College. Behavioral research shows that William occasionally migrates to the tropics to seek out Hoatzins, pangolins, and sloths, but mostly socializes with his age cohort in urbanized areas of eastern North America. He is short-sighted, slow to react, and a poor swimmer.

Skyline copyright Michael Mondville

One Way Light Pollution Impacts Birds

Skyline copyright Michael Mondville
Boston’s bright lights create a hazy glow on the horizon that can be seen for miles. Photo © Michael Mondville

Migrating birds are attracted to artificial light at night, and ornithologists are just beginning to understand how that affects their survival.

Recent studies show that the diffuse glow of entire cities can draw migrating birds towards them—and away from more suitable habitat.

There are already hundreds of records of mesmerized birds fluttering around single, isolated sources of bright light— from thousands of migrants trapped in the beams of mile-high searchlights in New York City, to dozens of warblers gathering at the windows of lighthouses.

But until recently, there was limited evidence for how light pollution across an entire region affects where migrants rest and feed.

Radar studies show “clouds” of birds near cities 

To test if birds gather disproportionately in brightly-lit cities, migration ecologists looked to doppler radar data. This is the same radar used to create weather forecasts across the country. Doppler radar reveals the density of particles in the air, whether it’s rain, birds, or aircraft, so it’s useful for remotely observing which areas migrating birds are using the most.

Naturalists might expect that migratory birds gravitate towards undeveloped areas, just as most do when they aren’t migrating. But this isn’t necessarily true, according to a team led by scientists from the University of Delaware.

In fact, radar signals consistently show more migrants pausing within a couple of miles of brightly-lit areas than anywhere else within around 30 miles. Migrant density peaks again 50-60 miles away, where the glow of lights on the horizon is dimmer or invisible.

These graphs show the density of migrating birds relative to major sources of light pollution like cities in spring (left) and fall (right) migration. Source: Cohen et al. (2020) (axis labels added).

This suggests that artificial light from cities is drawing in birds from greater distances than once believed. The authors of the study write that this pattern risks “impeding [birds’] selection for extensive forest habitat.” 

They go on to caution that “high‐quality stopover habitat is critical to successful migration, and hindrances during migration can decrease fitness.”

Prioritizing Urban Greenspaces for Birds

Migratory birds’ attraction to artificial light may be one reason behind the surprisingly excellent birding at greenspaces in cities—something birders have known about for a long time, but struggled to fully explain.

A canopy of trees meets Boston’s skyline, as seen from Mt. Auburn Cemetery in Watertown. Source: Wikimedia commons

Take Mount Auburn Cemetery, for example: it’s arguably the most famous site in the Northeast to see big numbers of warblers in spring. New York City’s Central Park, too, offers excellent birding that can rival—or outmatch—spring migration in intact forests.

But despite their attraction to the bright glow of cities, birds face increased hazards in urban environments. Most migratory birds feed exclusively on insects, which are harder to come by in cities, and urban ecosystems host more predators per square mile than other habitats.

Modifications as simple as planting native species, reducing insecticides, adding understory and mid-story habitat, or controlling predators could give migrants a much-needed boost at these sites. As long as light pollution continues to be an issue, improving urban habitat and reducing hazards remains important work.

A Harlequin Duck in Western Mass: Out of Place, or Right at Home?

Harlequin Ducks may not be the rarest ocean-going duck in Massachusetts, but they require a more specific habitat than any other kind of waterfowl: rocky, jagged coastlines with rough surf and abundant shellfish.

In fact, according to eBird, nobody had ever documented Harlequin Ducks more than a couple of miles inland in Massachusetts—until New Year’s Day 2021 when a local birder found a first-year male Harlequin on the fast-flowing Millers River in Turner’s Falls, MA, more than 120 miles away from the coast.  

The rocky Millers River was apparently good enough habitat for this young male Harlequin Duck. Photo © James Smith
The rocky Millers River was apparently good enough habitat for this young male Harlequin Duck. Photo © James Smith

Powerful Rivers are Western Harlequins’ Summer Home

While it’s surprising to see this duck inland in Massachusetts, Harlequins in other parts of the country actually spend half of their lives on fresh water. In the Rocky Mountains and the Cascades of the West, these patchily-distributed ducks breed in fast flowing, whitewater rivers.

The Millers River is well-known among paddlers for its fast current and rough stretches. Not many rivers in Massachusetts have the wide expanses of rapids that Harlequins prefer, making the Millers a likely candidate for our first inland record of this species.

Even Wandering Birds Follow Habitat Guidelines

This sighting is a great example of how rigidly habitat preferences govern  where birds are found, even in cases when birds show up in unusual geographic regions.

Most vagrant birds (that is, birds outside of their normal range) also stick to their usual habitats, or the closest thing they can find. Massachusetts’ last sighting of a Tropical Kingbird, for example, showed up in the brushy fields of Rock Meadow in Belmont—a fair local approximation of the low plains a prefers in the extreme Southwest.

And, true to its name, a Barn Owl that strayed farther north than normal was spotted taking shelter in the rafters of a high-ceilinged wooden garage in Lexington.

Stay in the Know

If you’re interested in following along with the latest unusual sightings, check out our weekly rare bird reports!

Pine Siskin. Photo © Terri Nicker

Siskins and Grosbeaks and Purple Finches, Oh My!

Most bird species overwinter in the same general area from year to year. Not so with some finches. Around eight species of winter finch become nomadic in winter, sometimes crossing the continent in search of food.

One reason these birds don’t stick to an annual pattern is the annually shifting availability of their favorite foods. If conifer seeds and mountain-ash berries are abundant in Canada, winter finches stay put on their northern breeding grounds. In less fruitful years, they head off in search of their next meal.

Biologists and birders in Canada who keep track of seed availability are forecasting that this will be a good year for finch movements. Here’s what to look for this winter.

Purple Finches

Purple Finch
Purple Finches have more extensive color and a different shape than similar House Finches.

Purple Finches had a great breeding season in Canada, in part due to an outbreak of spruce budworm, their go-to summer food. But the new hordes of yearling birds will need more seeds and berries than what’s available this winter in the north, and we’re already seeing a big movement of them in Massachusetts.

At feeders, Purple Finches love to eat safflower seed, but they’ll also stop for black-oil sunflower and thistle seed. Unlike the similar-looking House Finch, Purple Finches have a reddish wash that extends all the way down their wings and back, and a thicker bill.

Pine Siskins

Pine Siskin. Photo © Terri Nicker
Pine Siskin © Terri Nicker

Siskins are the stars of the show so far this year. Pine Siskins have arrived early in Massachusetts in spectacular numbers (with some observers recording overhead movements of more than 2,000!) At feeders, these finches don’t stop for much other than thistle seed, or other seeds small enough for their narrow bills.  

Evening Grosbeaks

Evening Grosbeak © Jim Renault
Evening Grosbeak © Jim Renault

These bold-colored finches last irrupted into Massachusetts in 2018, a bit more recently than the other two finches on this list. Major irruption years were infrequent in the 1980s through 2000s, so it’s a pleasant surprise to see these birds again just two years after their last big movement through the region. At feeders, these thick-billed birds prefer larger seeds, like black-oil sunflower.

Bonus species: Red-breasted Nuthatches

Red-breasted Nuthatch
Red-breasted Nuthatch

While not technically a finch, this species is nearly as nomadic. Red-breasted Nuthatches are year-round residents in high-elevation coniferous forests, and normally, they only visit the rest of the state in winter. But this summer and fall saw several big pushes of Red-breasted Nuthatch into Eastern Mass as well, and it’s a real possibility that they’ll continue through the winter in great numbers.

All of these species have arrived earlier than in most irruption years. That leads to a question of whether or not they’ll persist all winter in Massachusetts. It’s possible that these birds are mostly transients on their way even farther south: feeder-watchers are reporting that flocks of winter finches are showing up for a day and leaving, and grosbeaks and siskins have already been reported as far south as the Gulf Coast.

This is a great winter to hang up some feeders and see what happens!

Red-tailed Hawk copyright George Brehm

Fall Hawk Migration is in the Air

Hawks, falcons, and vultures are among the few groups of birds that migrate during the day.

Unlike songbirds and waterfowl, which migrate under cover of night, raptors are actually visible as they make their long journeys across continents.

Although hawks pass by some sites by the hundreds or thousands, that doesn’t necessarily mean you can see them from any site on any day of the season. To find your best day and destination, you have to think like a hawk.

Red-tailed Hawk copyright George Brehm
Red-tailed Hawk © George Brehm

Riding the Airwaves

Raptors have one goal when migrating: use as little energy as possible to make it to their destination. So, they seek out rising air currents to help them gain altitude without flapping. 

Air rises as it is heated by the warmth of the ground (a “thermal”), or pushed upwards by passing over a hill or mountain (an “updraft”). Raptors circle inside these columns of rising air as it carries them upwards. As the air cools and stops rising, raptors exit and glide for miles, slowly losing altitude until they find another column (or start flapping).

Hawks often end up riding the same air current together, forming a rising spiral of birds, or a “kettle.” Kettling isn’t actually a social behavior, even if it looks like the hawks are flying together. Thermal-surfing raptors are simply taking advantage of the most efficient route, like drivers on a highway.

Cool Weather, Hot Hawkwatching

Thermals are strongest when the ground is much warmer than the air. Hawkwatching can be excellent when a cold front moves through, bringing cold air over the (temporarily) much warmer ground and sending thermals spiraling upwards.

Cold fronts are often accompanied by winds from the north, which are conducive to southbound raptors in the fall. When clear, cold air moves in from the north after many days of poor migration conditions (either rain or strong winds from the south), unusually high numbers of restless raptors can be seen migrating at once.

Timing is Everything

Mid-September is prime season for viewing Massachusetts’ most numerous and conspicuous raptors, like Broad-winged Hawks and Ospreys, as well as less common species like American Kestrels and Sharp-shinned Hawks. As the season cools, the mix shifts a little, but the hawkwatching often stays good until late October and tapers off into November.

If you want to plan a trip to see migrating raptors this season, check out our list of hawkwatching sites as well as resources from the Eastern Massachusetts Hawk Watch club.

Evening Grosbeak © MDF (CC BY-SA 3.0)

An Epic Winter For Nomadic Finches

Every few winters, several bird species abandon their normal wintering areas to our northwest, and move into Massachusetts by the thousands. While distantly related, redpolls, siskins, and grosbeaks all rely on food sources that go through boom and bust cycles, peaking and crashing every 3-6 years. When conifer and birch seeds are scarce in Canada’s boreal forest, these loosely-related species irrupt southwards in search of food.

The core group of these birds are collectively called “winter finches,” and this year will be huge for them!

Species On The Move In 2018:

Evening Grosbeaks

Evening Grosbeak © MDF (CC BY-SA 3.0)

Evening Grosbeak © MDF (CC BY-SA 3.0)

This year, these sunset-yellow, black and white-patterned finches are the stars of the show. It’s been a few years since Massachusetts saw any wintertime movement of Evening Grosbeaks into the state, and the last major irruption was in the 1990s.

Unlike many winter finches, Evening Grosbeaks seem equally happy feeding on several food types—both fruits and large seeds. They’ll come to feeders, but their bulky size means that they prefer large platform feeders and will avoid tube feeders. Their fruit-eating tendencies means that they often move south with two other frugivores, Bohemian Waxwings and Pine Grosbeaks, which may show up in smaller numbers this year.

Common Redpolls

Common Redpoll © Simon Pierre Barrette

These finches specialize in eating birch catkins, and birches are the best place to look for them. Ornithologists predict a big redpoll incursion into the northeast this winter. Redpolls got a slow start in Massachusetts this year, but are starting to show up in larger numbers, especially in the Northern and Western parts of the state.

Red-breasted Nuthatches

Red-breasted Nuthatch © Richard Alvarnaz

While technically not a winter finch, this species is nearly as nomadic, and this year is big for them. Their relative, the White-breasted Nuthatch, is a year-round resident and common backyard bird.

Red-breasted Nuthatches made a very early southward movement this year, with many appearing as early as late summer, heralding a major incursion of wandering finches later in the season.

Pine Siskins

Pine Siskin © Terri Nickerson

Siskins are showing up in abundance right now! These small finches with yellow-streaked wings love small seeds. Hang up feeders filled with nyjer or thistle seeds to take advantage of their incursion.

Where To Look

In addition to feeders, groves of spruce trees can be great places to look for seed-eating winter finches like siskins and crossbills. Redpolls are drawn to birch catkins. Fruit-eating finches often take well to ornamental varieties of crabapples, which bear fruit through the winter, so look for grosbeaks and waxwings anywhere large groves of these have been planted—which sometimes means office parks, parking lots, and gardens.

Feeders Up!

Last year was an excellent year for cone crops in Manitoba, Ontario and Quebec, leading to increased reproduction for seed-eating birds. This means that while spruce seeds, birch catkins, and mountain-ash berries are scarce in Ontario and Quebec, there will be loads of hungry birds looking for them—and moving into the US in search of food.

Birdfeeders do help birds survive harsh winters when food is scarce (though there’s a some This is a great time of year to put out black-oil sunflower seeds and nyjer seeds—two of winter finches’ favorite staples at birdfeeders.

For a more in-depth look at this year’s incursion of Evening Grosbeaks and their shifting distribution in New England, check out our birding blog.

Rose-breasted Grosbeak

Spring Migration is Finally Here

On the evening of Tuesday, May 1, a wave of migratory birds arrived in Massachusetts. While some early-migrating species have been trickling in since April, Wednesday, May 2, marks the beginning of the season for our most colorful migrants. Scarlet Tanagers, Yellow Warblers, melodious Wood Thrushes, and a host of other species have finally arrived after waiting out winter in the tropics. 

Rose-breasted Grosbeaks are one of dozens of showy migratory species. Photo © Will Freedberg

Understanding Migration

Most migratory songbirds fly north under the cover of darkness, out of sight of daytime predators like falcons and hawks. Sometimes, it’s possible to hear them in quiet, open spaces: a faint “chip” noise is the telltale sign of a warbler flying overhead. Most nights, you might just hear one ever few minutes, but on nights with heavy migration, it’s possible to hear a flight call every second.

These birds prefer to migrate on nights with southwest winds, which speed them on their journey north. In fact, Tuesday’s southwest winds combined with recent bird reports from New York were the key tip-offs that migrants would arrive today.

These birds journey north over several nights, with most stopping to feed along the way and flying with a southwest wind at their backs. In fact, after staying put during last week’s steady northerly winds, this first push of birds flew into Massachusetts as soon as the winds shifted southwest.

Read the Radar

The scale of bird migration is astounding. So huge, in fact, that you can watch it unfold across entire regions on radar. Doppler radar, normally used to detect weather patterns like thunderstorms, regularly picks up “clouds” of migrating birds, allowing scientists to study migration patterns on a continental scale. To learn how to predict bird migration with radar, check out our introduction to the topic and specific instructions on how to read radar signals.

Canada Warbler. Photo © Will Freedberg

Tips For Watching Warblers

One of the joys of spring migration is that surprising birds can show up just about anywhere. While migratory species rely on undisturbed forests and shrublands to breed, many also pass through urban and suburban parks on their way north. Any grove of trees, whether in the Boston Public Garden or a suburban backyard, is a great place to check for warblers, orioles, grosbeaks, and other goodies.

Look for these colorful visitors in the highest parts of trees, but also around dense cover like thickets. But the real key is waking up early. Most migrants are active just after dawn, and turn quiet by mid-morning.

Good luck! If you see anything good out there, let us know on our Facebook page.