Princeton’s Institute Woods is among the best places to view spring migrators

By Ilene Dube

Photo-Illustrations by Jeffrey E. Tryon

Birds by Maria Stezhko (shutterstock.com) 

At this writing—a cold gray winter day—it’s hard to imagine that in May, the skies will fill with migrating birds, bringing color, song, and beauty to the treetops.

“Spring warbler watching is not just birding. It is a social phenomenon, a ritual, a happening like maple sugaring in Vermont or the opening day of trout season in Pennsylvania,” writes eminent ornithologist Pete Dunne. “People who never lift binoculars at any other time of year X out their Saturday mornings in May and join thousands of kindred souls searching for treasure in the treetops.”

One of the top places in the world to see spring-migrating warblers is the Institute Woods at Princeton’s Institute for Advanced Study. The Institute Woods and Charles H. Rogers Wildlife Refuge form a 300-acre tract of deciduous forest bounded on the east by the wet woodlands and marsh. Crisscrossed by a network of trails and a sewer right-of-way, the Woods includes a small area of virgin forest and harbors a good number of bird species, particularly during the songbird migration seasons. Because of the Institute Woods’ reputation, birders come from all over. There have been groups from the Summit Nature Club, the Trenton Naturalist Club, the Montclair Nature Club, and the Watchung Nature Club, as well as local groups.

On a typical Saturday in May, cars line both sides of West Drive, leading to the Rogers Refuge. An observation platform overlooks the main section of the marsh. More 190 species of birds have been seen here, and it is possible to see as many as 30 species of warblers in a single day

“Necks crane skyward, and high overhead the canopy vibrates with the frenetic movement of feeding warblers—Tennessees, Blackpolls, Parulas, Cape Mays, and the flame-throated Blackburnians,” continues Dunne. “Lower, in the understory, there are Canada Warblers (with their bold, staring spectacles), licorice-striped Black-and-Whites, elegant Black-throated Blues, and flashing male Redstarts (the bird whose coal-black and crimson pattern gave rise to its Spanish name, the little torch). Hugging the ground, leaving no niche unfilled, are Northern and Louisiana Waterthrushes and skulking Kentuckys; later in the season, sounding the death knell of spring migration, is the elusive wraith of the shadows, the Mourning Warbler.”

A Tranquil Environment

The Institute for Advanced Study, founded in 1930 by Louis Bamberger and Caroline Bamberger Fuld, gradually acquired most of the land between 1936 and 1945, providing a tranquil environment for scholars engaged in theoretical research and intellectual inquiry. Prior to then, most of the land had been farmed or planted as an orchard. General George Washington marched his troops through the Institute Woods just prior to engaging in the Battle of Princeton in 1777. In 1950, Institute Director J. Robert Oppenheimer dedicated a Founders’ Walk, which included four miles of trails and paths, and the building of a suspension bridge.

Today, a working farm abuts the western end of the woods. An old trolley line between Trenton and Princeton marks the northern edge of the woods behind the Institute fields.

A refuge for wildlife as well as ideas, the peaceful environment of the woods provides opportunities for solitary contemplation along with chance encounters with the many species of animals that inhabit the grounds. 

The Stony Brook flows through and is bordered by a broad flood plain, which has abundant beds of spring wildflowers such as yellow trout lilies, pink and white spring beauties, and purple violets. Aspen, gray birch, beech, oak, hickory, dogwood, sweet gum, and red maple trees provide habitat for summer breeding and spring and fall migrating birds.

Since 1997, the Institute has been the steward of these 589 acres of woods, wetlands, and farmland. The per–m-anent easement protects a 56-mile greenway network crit-ical for the feeding and nesting of birds on the Atlantic flyway, and a unique laboratory of more than 45 species of trees for studies of forest succession.

According to the New Jersey Trails Association website, these lands are not a public park, but the Institute graciously allows the public to use the lands under terms of the conservation easement that preserved the lands in perpetuity.

One of the reasons the Institute Woods is so good for bird watching is its location, along the line where the Coastal Plain geographic region meets the Piedmont regions just north of the Pine Barrens. The Institute Woods’ abundant plant life and hardwood trees provide a greater food source than the Pine Barrens.

Rogers Wildlife Refuge

The 39-acre Rogers Wildlife Refuge borders the Institute Woods and contains bush areas, thickets, woods, and the north bank of the Stony Brook. It was acquired in 1968 by what is now the Princeton Environmental Commission by a conservation easement, and memorializes Charles H. Rogers, a nationally-known ornithologist who, along with Thomas Southerland, played a key role in establishing the sanctuary. Rogers passed away in 1977, but Southerland, who with his wife, Margot, ran Princeton Nature Tours from 1981 to 2001, still leads birding expeditions to the Institute Woods and Refuge. His tours are the longest continuing course Princeton Adult School has offered, he says. Doctors, faculty members, even a gold medalist diver have participated in his trips. This year it will be held on Saturday, May 12—register at Princetonadultschool.org.

Southerland, who moved to Princeton in 1962, assisted Princeton Physics Professor Lyman Spitzer, whose work led to both the Hubble Telescope and Princeton Plasma Physics Lab. At the University, Southerland got involved in the first Earth Day. He organized a chapter of the Sierra Club, and authored books and studies on environmental issues. He also served on the Princeton Township Conservation Commission and chaired the Stony Brook-Millstone Watershed Association. With Princeton Nature Tours, he has identified more than 411 different species of birds in New Jersey, 741 in North America, and more than 4,100 worldwide.

These days, Southerland admits that the Institute Woods is no longer as popular for warblers as it was in its heyday. “One of the bumps is that the deer are taking over, eating all the groundcover—except the garlic mustard. No one wants the garlic mustard,” he says. “Ovenbirds, Thrushes, and Towhees need good vegetation, such as jack-in-the-pulpit, to feed on the ground.” Since White Buffalo was contracted to cull the deer, the problem has improved somewhat, although last year’s warm winter resulted in a robust herd.

Another factor has been development, such as at Canal Point, says Southerland, which impinged on habitat. “There’s development everywhere,” he admits.

Stick To The Edge

“When you look for birds, whether in New Guinea or Princeton, it’s best to walk along the edge, or along the road,” he says. “The edge gets the sun, and they get the fruit and the insects. But when the edge is destroyed, and you don’t have buffer zones, you open up to Blue Jays and Grackles and Starlings—suburban birds.” Because of these invasive birds, it is harder for migrators to breed—they have to compete with birds that wouldn’t normally be here. And speaking of invasives, “because of how the Phragmites (large perennial grasses in wetlands) has grown, you can’t even see the pond anymore.”

Deforestation in Borneo, due to the harvesting of palm oil, among other things, also effects the bird population migrating through New Jersey, Southerland says. Without the large blocks of inter-connected forest, hundreds of species could become extinct. Large mammals such as orangutans are already affected. Southerland cites research by Princeton Professor of Ecology, Evolutionary Biology, and Public Affairs David Wilcove on how climate change and the fragmenting of the forest negatively affect animal migration.

Still, Southerland has high hopes of seeing Grosbeak, Scarlet Tanager, Redstarts, and Wood Thrush in the Institute Woods this year. “We always used to see Yellow Warblers around the observation tower, but last year we didn’t see a one.”

Cowbirds, he says, have increased in number. The Brown-headed Cowbird is a brood parasite, meaning that it lays its eggs in nests of other species. A female Cowbird quietly searches for female birds of other species that are actively laying eggs. Once she has found a suitable host, the Cowbird will sneak onto the resident bird’s nest when it is away, usually damage or remove one or more egg, and replace that egg with one or more of her own. The foster parents then unknowingly raise the young Cowbirds, at the expense of their own offspring. 

“One year, in our yard, we saw a female Cardinal feeding a Cowbird in her nest,” says Southerland.

It’s a jungle out there.

Wood ducks often breed in Princeton’s tree streets, in the cavities of trees. “The female calls to the young, and they suddenly drop out of the tree. ‘Welcome to Earth,’ she seems to be saying. Then, at nighttime, she takes them to Lake Carnegie.” One year, back in the 1970s, Southerland and his wife got the police to hold up traffic on Nassau Street so the chicks could safely cross.

Field Trips

On Sunday, May 6, 8am, and Saturday, May 19, 8am, Brad Merritt will offer field trips to the Institute Woods for the Washington Crossing Audubon Society. Phone (609) 921-8964 to register. Merritt, retired from the state police where he worked in emergency management, has been birding since he was 15. The Rocky Hill resident majored in biology with an emphasis on ornithology and zoology at Allegheny College and has been leading field trips since he was in his 20s.

“The Institute Woods used to be one of best warbler spots in country,” he says. He agrees with Southerland that it’s not like it was in the ’60s, ’70s, and ’80s because “the deer population has browsed the woods down to nothing, there’s no understory.” Since deer culling began, he has observed spicebush coming back and seen more thrushes and warblers. “Breeding birds, Kentucky Warblers, and ground nesters all want the spicebush. The understory is essential for warblers.”

Merritt has also noticed the disappearance of inch worms. “They used to drop from everywhere. Now you don’t see them as much. The biology of the forest might not be what they used to lay eggs on. There used to be a beech grove, but it has died out. Hurricanes like Sandy also caused damage. Forests have a natural progression,” he explained, saying that they change as trees grow old and die.

Climate change may affect the arrival dates of warblers, says Merritt, as well as how late they stay. “They arrive after the thaw when insects, their food source, are out. The thing about climate change is that it could be 50 years before we see changes, and people don’t make decisions about things that far into the future.”

Birders accompany Merritt because they want to see the beautiful colors and hear the songs, “but warblers can be difficult to see behind trees,” he says. “We encourage people who are new to come on our trips, and to take time to learn about the bird: how it feeds, where it nests. It can be frustrating for new birders, even for experienced birders—warblers can drive you up the wall when they get behind leaves to feed on insects.”

One common beginner frustration is how to focus binoculars on the elusive spot where fellow birders are pointing, losing sight of the bird while bringing the binoculars to the eyes. Merritt suggests not looking down at the binoculars, but keeping your eye on where the bird is as you raise the lenses to your eyes.

Sound, Sight, And Habitat

Beginning birders study field guides and work out identifications point by point, but veterans rely on their ears, finely tuned over the course of seasons, according to Dunne. Merritt agrees: The best way to identify a bird is by ear. “Walking through the Institute Woods, if you know the song of a warbler, you know to stop and look, although you may not see anything for 10 minutes.” He teaches the Roger Tory Peterson approach of looking for field marks. “If you see a red bird with black wings, you know it’s a Tanager.” He looks at shape and size of the bird, as well as the way it flies. “You know it’s a Blue Jay by the way it paddle flies, or it’s a Goldfinch if it ambulates when it flies.” Habitat, too, helps to identify. “Is it out in fields or in deep woods? Where does it nest? If it’s a ground nester, then don’t look up for it.”

Birding enthusiasts can study books, listen to tapes, look at the Cornell School of Ornithology’s All About Birds website, or go out in the field with a group of knowledgeable birders, he says. “Every day is an adventure in the woods. The Institute Woods is where Einstein used to walk and think, so it has to be a great place.”

Dr. Henry Horn, Princeton University Emeritus, Department of Ecology and Evolutionary Biology, has conducted extensive research in the Institute Woods for more than 40 years, and calls it “one of the most renowned natural areas in central New Jersey.” He says his interest in natural history began with an obsession with birds, which led to obsessions with trees, butterflies, and wildflowers.

While identifying them is nice, he says, he just likes to watch them: their beauty, the ways in which they fly. He’ll be leading A Walk on the Wild Side: Exploring the Institute Woods through Princeton Adult School on Saturday, May 12, 10 am.

Winnie and Fred Spar will lead the annual Birdathon for Washington Crossing Audubon on May 12, 8am—meet in the Rogers Refuge. 

Looking for something for the whole family? Howell Living History Farm is offering a Family Bird Excursion: Naturally Friends Series on Sunday, May 6, 1-3pm. The naturalist will lead an afternoon of family-style birding. Children will participate in a Bird Spotting Challenge while parents enjoy the calls, songs, and sights of spring migration. Go to howellfarm.org.

Looking for birds can be hit or miss, so it’s good to have other wildlife on your list of what to see. The New Jersey Mycological Association offers mushroom forays in the Institute Woods during warbler season, which coincides with morel season. At press time the schedule was not yet finalized; check njmyco.org.