American Redstart – LIFE IN THE LOWER SUSQUEHANNA RIVER WATERSHED

May 24, 2024May 25, 2024

Arboreal Birds and Tent Caterpillars

During the past week, we’ve been exploring wooded slopes around the lower Susquehanna region in search of recently arrived Neotropical birds—particularly those migrants that are singing on breeding territories and will stay to nest. Coincidentally, we noticed a good diversity of species in areas where tent caterpillar nests were apparent.

Eastern Tent Caterpillar Nest — The conspicuous nest of the Eastern Tent Caterpillar (Malacosoma americanum), a native species of moth. The first instar of the larval caterpillars hatch in early spring from egg masses laid on the limbs of the host tree by an adult female moth during the previous spring. Soon after they begin feeding on the host tree’s first tender shoots, these tiny, seldom-noticed larvae start communal construction of a silk tent to act as a shelter and greenhouse-like solar collector that will both provide protection from the elements and expedite their growth.

Here’s a sample of the variety of Neotropical migrants we found in areas impacted by Eastern Tent Caterpillars. All are arboreal insectivores, birds that feed among the foliage of trees and shrubs searching mostly for insects, their larvae, and their eggs.

The Yellow-throated Vireo nests, feeds, and spends the majority of its time feeding among canopy foliage.

The Eastern Wood-Pewee is a flycatcher found in mature woodlands. It feeds not only among the limbs and leaves, but is an aerial predator as well.

The Northern Parula nests in mature forests along rivers and on mountainsides, particularly where mature trees are draped with thick vines.

The Hooded Warbler (Setophaga citrina) is found among thick understory growth on forested slopes.

The Ovenbird builds a domed, oven-like nest on the ground and forages in the canopy.

The Kentucky Warbler (Geothlypis formosa) nests in woodland undergrowth, often near steep, forested slopes.

The Worm-eating Warbler (Helmitheros vermivorum) nests among woody understory growth on forested hillsides.

The Scarlet Tanager is often difficult to observe because of its affinity for the canopy of mature forest trees.

In the locations where these photographs were taken, ground-feeding birds, including those species that would normally be common in these habitats, were absent. There were no Gray Catbirds, Carolina Wrens, American Robins or other thrushes seen or heard. One might infer that the arboreal insectivorous birds chose to establish nesting territories where they did largely due to the presence of an abundance of tent caterpillars as a potential food source for their young. That could very well be true—but consider timing.

**Already Gone-** By the time Neotropical migrants arrive in our area, the larval stages of the Eastern Tent Caterpillar’s life cycle are already coming to an end. The nests that these native insects constructed to capture the energy of the springtime sun have allowed the larvae to exit and browse foliage when conditions were suitable, then return for shelter when they were not. While inside, the larvae could move among the chambers of their structure to find locations with a temperature that best suited their needs. Therein the solar heating and communal warmth sped up digestion and growth.

Having left arboreal environs, Eastern Tent Caterpillar larvae are now food for ground-feeding birds like our resident Wild Turkeys. They need only get past the bristly hairs on the caterpillar’s back and the foul taste that may result from its limited diet of cyanogenic Black Cherry leaves.

The arboreal Yellow-billed Cuckoo (seen here) and its close relative the Black-billed Cuckoo (Coccyzus erythropthalmus) are the two species of birds in our area known to regularly feed on bristly tent caterpillars. But having just arrived from the tropics to nest, they’ll need to rely on other insects and their larvae as sources of food for their young.

Black Cherry defoliated by Eastern Tent Caterpillars. — Final-instar Eastern Tent Caterpillars often defoliate Black Cherry trees before moving to the ground to pupate. Their timing allows them to feed on the fresh foliage while it is still young and tender, and to largely avoid becoming food for the waves of Neotropical birds that arrive in the lower Susquehanna basin in May.

So why do we find this admirable variety of Neotropical bird species nesting in locations with tent caterpillars? Perhaps it’s a matter of suitable topography, an appropriate variety of native trees and shrubs, and an attractive opening in the forest.

An American Redstart singing in a Black Cherry. Unlike others in the vicinity, this tree nestled among several very large Eastern White Pines showed no signs of tent caterpillar activity. It may be that for one reason or another, no adult female moth deposited her eggs on this particular tree. During our visits, Black Cherry was but one of the diverse variety of native trees and shrubs found growing on the sloping topography that created attractive habitat for the nesting birds we found. We happened to notice that a majority, but not all, of those Black Cherry trees were impacted by Eastern Tent Caterpillars.

Black Cherry in Flower — The end of the Eastern Tent Caterpillar’s larval surge may spell the end of their nests for the year, but it’s not the end for the Black Cherry and other host trees in the Prunus (cherry) and Malus (apple) genera. Because it’s still early in the season, they have plenty of time to re-leaf and many will still flower and produce fruit. Those flowers and foliage will attract numerous other insects (including pollinators) that benefit breeding birds.

The Blue-winged Warbler inhabits shrubby breaks in the forest such as this utility right-of-way where Black Cherry trees have sprouted after their seeds arrived in waste deposited by fruit-eating (frugivorous) birds. Already attractive to a variety of insectivores, these openings soon lure egg-laying Eastern Tent Caterpillar moths to the cherry trees growing therein. Even in dense forest, a small clearing created by a cluster of dead trees makes good bird habitat and will sooner or later be visited by fruit-eating species that will inadvertently sow seeds of Black Cherry, starting yet another stand of host trees for Eastern Tent Caterpillars. It’s the gap in the forest that often attracts the birds, some of which plant the host trees, which sometimes entice Eastern Tent Caterpillar moths to lay their eggs.

Red-Eyed Vireo — **Adapt and Reuse-** A Red-eyed Vireo visits an Eastern Tent Caterpillar nest…

Here in the Lower Susquehanna River Watershed, the presence of Eastern Tent Caterpillar nests can often be an indicator of a woodland opening, natural or man-made, that is being reforested by Black Cherry and other plants which improve the botanical richness of the site. For numerous migratory Neotropical species seeking favorable places to nest and raise young, these regenerative areas and the forests surrounding them can be ideal habitat. For us, they can be great places to see and hear colorful birds.

May 8, 2024May 14, 2024

A Pre-dawn Thunderstorm and a Fallout of Migrating Birds

In recent days, the peak northbound push of migratory birds that includes the majority of our colorful Neotropical species has been slowed to a trickle by the presence of rain, fog, and low overcast throughout the Mid-Atlantic States. Following sunset last evening, the nocturnal flight resumed—only to be grounded this morning during the pre-dawn hours by the west-to-east passage of a fast-moving line of strong thundershowers. The NOAA/National Weather Service images that follow show the thunderstorms as well as returns created by thousands of migrating birds as they pass through the Doppler Radar coverage areas that surround the lower Susquehanna valley.

Sterling, Virginia, Doppler Radar west of Washington, D.C., at 4:00 A.M. E.D.T. indicates a dense flight of northbound migrating birds located just to the south of the approaching line of rain and thunderstorms over the State College, Pennsylvania, radar coverage area. (NOAA/National Weather Service image)

More northbound birds are indicated at 4 A.M. by the radar station located at Dover, Delaware… (NOAA/National Weather Service image)

…and by the Mount Holly, New Jersey, radar site. (NOAA/National Weather Service image)

Many of the migrating birds shown here over the Binghamton, New York, radar station at 4 A.M. probably overflew the lower Susquehanna region earlier in the night. (NOAA/National Weather Service image)

And these birds over Albany, New York’s, radar station at 4 A.M. are mostly migrants that passed north over New Jersey and easternmost Pennsylvania last evening and during the wee hours of this morning. (NOAA/National Weather Service image)

Just after 4 A.M., flashes of lightning in rapid succession repeatedly illuminated the sky over susquehannawildlife.net headquarters. Despite the rumbles of thunder and the din of noises typical for our urban setting, the call notes of nocturnal migrants could be heard as these birds descended in search of a suitable place to make landfall and seek shelter from the storm. At least one Wood Thrush and a Swainson’s Thrush (Catharus ustulatus) were in the mix of species passing overhead. A short time later at daybreak, a Great Crested Flycatcher was heard calling from a stand of nearby trees and a White-crowned Sparrow was seen in the garden searching for food. None of these aforementioned birds is regular here at our little oasis, so it appears that a significant and abrupt fallout has occurred.

A White-crowned Sparrow in the headquarters garden at daybreak. It’s the first visit by this species in a decade or more.

Looks like a good day to take the camera for a walk. Away we go!

Along woodland edges, in thickets, and in gardens, Gray Catbirds were everywhere today. We heard and/or saw hundreds of them.

Many early-arriving Baltimore Orioles have already begun building nests. But widespread territorial fighting today may be an indication that some latecomer orioles became trespassers after dropping in on existing territories during the morning fallout.

No woodland chorus is complete without the flute-like harmony of the Wood Thrush. Look and listen for them in rich forests with dense understory vegetation.

Yellow-rumped Warblers can be especially numerous during migration but tend to peak prior to the arrival of the bulk of the Neotropical species. This was the only “yellow-rump” we encountered today. The majority have already passed through on their way to breeding grounds to our north.

If today you were to visit a streamside thicket or any type of early successional habitat, you would probably find this perky little warbler there, the Common Yellowthroat.

The Yellow Warbler likes streamside thickets too. You can also find them along lakes, ponds, and wetlands, especially among shrubby willows and alders.

Not all songbirds migrate at night. The Bobolink is an example of a diurnal (day-flying) migrant. They’re currently arriving in hay fields that are spared the mower until after nesting season.

While looking for Neotropical species and other late-season migrants, we also found numerous early arrivals that had already begun their breeding cycles. We discovered this Blue-gray Gnatcatcher on its nest in a Black Walnut tree…

There’s obviously more spring migration to come, so do make an effort to visit an array of habitats during the coming weeks to see and hear the wide variety of birds, including the spectacular Neotropical species, that visit the Lower Susquehanna River Watershed each May. You won’t regret it!

Wood Ducks arrived in February and March to breed in the lower Susquehanna valley. Soon after hatching in April or May, the young leave the nest cavity to travel under the watchful gaze of their ever-vigilant mother as they search for food along our local waterways. If you’re fortunate, you might catch a glimpse of a brood and hen while you’re out looking at the more than one hundred species of birds that occur in our region during the first half of May. Good luck!

September 5, 2023September 17, 2023

Catch a Wave While You’re Sittin’ on Top of the World

During the recent couple of mornings, a tide of Neotropical migrants has been rolling along the crests of the Appalachian ridges and Piedmont highlands of southern Pennsylvania. In the first hours of daylight, “waves” of warblers, vireos, flycatchers, tanagers, and other birds are being observed flitting among the sun-drenched foliage as they feed in trees along the edges of ridgetop clearings. Big fallouts have been reported along Kittattiny Ridge/Blue Mountain at Hawk Mountain Sanctuary and at Waggoner’s Gap Hawk Watch. Birds are also being seen in the Furnace Hills of the Piedmont.

Here are some of the 300 to 400 warblers (a very conservative estimate) seen in a “wave” found working its way southwest through the forest clearing at the Second Mountain Hawk Watch in Lebanon County this morning. The feeding frenzy endured for two hours between 7 and 9 A.M. E.D.T.

Tennessee Warblers at Second Mountain Hawk Watch. — Tennessee Warblers (Leiothlypis peregrina) were very common among the migrants seen this morning on Second Mountain.

Tennessee Warbler at Second Mountain Hawk Watch. — An adult male Tennessee Warbler.

Nashville Warbler at Second Mountain Hawk Watch. — A Nashville Warbler.

Chestnut-sided Warbler at Second Mountain Hawk Watch. — A Chestnut-sided Warbler.

Cape May Warbler at Second Mountain Hawk Watch. — Cape May Warblers were another common species during the morning flight.

Magnolia Warbler at Second Mountain Hawk Watch. — Magnolia Warblers were frequently observed as well.

Black-and-white Warbler at Second Mountain Hawk Watch. — A Black-and-white Warbler exhibiting its nuthatch-like feeding behavior.

Blackburnian Warbler at Second Mountain Hawk Watch. — A Blackburnian Warbler.

Black-throated Green Warbler at Second Mountain Hawk Watch. — Black-throated Green Warblers were numerous.

Bay-breasted Warbler at Second Mountain Hawk Watch. — A Bay-breasted Warbler.

Wilson's Warbler at Second Mountain Hawk Watch. — This was the only Wilson’s Warbler discerned among the hundreds of warblers seen in a “wave” on Second Mountain this morning.

Not photographed but observed in the mix of species were several Black-throated Blue Warblers and American Redstarts.

In addition to the warblers, other Neotropical migrants were on the move including two Common Nighthawks, a Broad-winged Hawk, a Least Flycatcher (Empidonax minimus), and…

Scarlet Tanager at Second Mountain Hawk Watch. — At least half a dozen Scarlet Tanagers were in the treetops.

Ruby-throated Hummingbird at Second Mountain Hawk Watch. — And no less than 23 Ruby-throated Hummingbirds were counted cruising southbound past the lookout at Second Mountain Hawk Watch today.

Then, there was a taste of things to come…

Red-breasted Nuthatch at Second Mountain Hawk Watch. — One of 3 Red-breasted Nuthatches filling the air on the mountaintop with calls reminiscent of a toy tin horn. Will this summer’s forest fires in Canada prompt a significant invasion of this and other birds including winter finches in coming months? Time will tell.

Seeing a “wave” flight is a matter of being in the right place at the right time. Visiting known locations for observing warbler fallouts such as hawk watches, ridgetop clearings, and peninsular shorelines can improve your chances of witnessing one of these memorable spectacles by overcoming the first variable. To overcome the second, be sure to visit early and often. See you on the lookout!

May 11, 2021May 13, 2021

Maximum Variety

You’ll want to go for a walk this week. It’s prime time to see birds in all their spring splendor. Colorful Neotropical migrants are moving through in waves to supplement the numerous temperate species that arrived earlier this spring to begin their nesting cycle. Here’s a sample of what you might find this week along a rail-trail, park path, or quiet country road near you—even on a rainy or breezy day.

The Black-throated Blue Warbler is one of more than two dozen species of warblers passing through the Lower Susquehanna River Watershed right now. Look for it in the middle and bottom branches of deciduous forest growth.

The Veery and other woodland thrushes sing a melodious song. Veerys remain through the summer to nest in damp mature deciduous forests.

The American Redstart, this one a first-spring male, is another of the variety of warblers arriving now. Redstarts nest in deciduous forests with a dense understory.

Adaptable inquisitive Gray Catbirds are here to nest in any shrubby habitat, whether in a forest or a suburban garden.

Blue-gray Gnatcatchers (Polioptilia caerulea) arrive in April, so they’ve been here for a while. They spend most of their time foraging in the treetops. The gnatcatcher’s wheezy call alerts the observer to their presence.

Look way up there, it’s a pair of Blue-gray Gnatcatchers building a nest.

The Eastern Phoebe, a species of flycatcher, often arrives as early as mid-March. This particular bird and its mate are already nesting beneath a stone bridge that passes over a woodland stream.

Orchard Orioles (Icturus spurius) are Neotropical migrants that nest locally in habitats with scattered large trees, especially in meadows and abandoned orchards.

In the lower Susquehanna region, the Baltimore Oriole is a more widespread breeding species than the Orchard Oriole. In addition to the sites preferred by the latter, it will nest in groves of mature trees on farms and estates, in parks, and in forest margins where the canopy is broken.

The Warbling Vireo (Vireo gilvus) nests in big trees along streams, often sharing habitat with our two species of orioles.

Eastern Towhees arrive in numbers during April. They nest in thickets and hedgerows, where a few stragglers can sometimes be found throughout the winter.

The Yellow-breasted Chat (Icteria virens) is a migrant from the tropics that sometimes nests locally in thorny thickets. Its song consists of a mixed variety of loud phrases, reminding the listener of mimics like catbirds, thrashers, and mockingbirds.

Thickets with fragrant blooms of honeysuckle and olive attract migrating Ruby-throated Hummingbirds. Look for them taking a break on a dead branch where they can have a look around and hold on tight during gusts of wind.

The Eastern Kingbird, a Neotropical flycatcher, may be found near fields and meadows with an abundance of insects. In recent years, high-intensity farming practices have reduced the occurrence of kingbirds as a nesting species in the lower Susquehanna valley. The loss of pasture acreage appears to have been particularly detrimental.

Savannah Sparrows (Passerculus sandwichensis) can be found in grassy fields throughout the year. Large parcels that go uncut through at least early July offer them the opportunity to nest.

Male Bobolinks have been here for just more than a week. Look for them in alfalfa fields and meadows. Like Savannah Sparrows, Bobolinks nest on the ground and will lose their eggs and/or young if fields are mowed during the breeding cycle.

Cattail marshes are currently home to nesting Swamp Sparrows. Wetlands offer an opportunity to see a variety of unique species in coming weeks.

Shorebirds like this Solitary Sandpiper will be transiting the lower Susquehanna basin through the end of May. They stop to rest in wetlands, flooded fields, and on mudflats and alluvial islets in the region’s larger streams. Many of these shorebirds nest in far northern Canada. So remember, they need to rest and recharge for the long trip ahead, so try not to disturb them.

September 13, 2020October 4, 2020

A Visit to Second Mountain

If it can fly, there’s a pretty good chance it was at Second Mountain today.

What follows is a photographic chronology of some of today’s sightings at Second Mountain Hawk Watch at Fort Indiantown Gap in Lebanon County, Pennsylvania. We begin with some of the hundreds of migratory songbirds found at the base of the mountain along Cold Spring Road near Indiantown Run during the early morning, then we continue to the lookout for the balance of the day.

A Black-and-white Warbler (Mniotilta varia) searching the trunk of a tree for insects.

A Blackburnian Warbler high in the forest canopy.

A Black-throated Green Warbler bouncing from branch to branch as it feeds.

A Chestnut-sided Warbler lurks among the foliage.

One of a hundred or more Red-eyed Vireos found swarming the treetops, and occasionally the understory, while engaging in a wild feeding frenzy.

A male American Redstart. Judging by that gray hood, it’s probably experiencing its second fall migration.

Eyes were skyward at the Second Mountain Hawk Watch lookout as Broad-winged Hawks began streaming through during the mid-morning.

During the morning flight, Broad-winged Hawks including this adult floated by the lookout riding updrafts created by the south wind striking the face of the mountain ridge.

As the overcast became more scattered and more sunlight reached the ground, Broad-winged Hawks began riding thermal currents to gain altitude before gliding off to the southwest in continuance of their long trip to the tropics. At times, birds would disappear into the base of the clouds before ending their climb and sailing away.

Broad-winged Hawks rely principally upon amphibians and large insects like this bush katydid (Scudderia species) for sustenance. With freezing temperatures just around the corner, “broad-wings” must make their way to warmer climes early or risk starvation.

A Bald Eagle always gets observers looking.

One never quite knows what one may see when having a look around.

A Cape May Warbler (Setophaga tigrina) in the lookout hemlock.

A Black Saddlebags, one of several migratory dragonflies seen today.

An Osprey glides through in the afternoon glare.

A speedy Merlin thrilled observers with a close approach.

One must remember that Fort Indiantown Gap is an active military installation, so from time to time training and drilling exercises may interrupt bird observation activities at the Second Mountain Hawk Watch.

Today, speedy A-10 Warthog attack aircraft piloted by members of the Maryland Air National Guard based at Glenn Martin Field thrilled observers on the lookout with several close passes during their training runs.

The total number of Broad-winged Hawks observed migrating past the Second Mountain lookout today was 619. To see the daily raptor counts for Second Mountain and other hawk watches in North America, and to learn more about each site, be sure to visit hawkcount.org

May 17, 2020May 18, 2020

Big Flight Last Night

Birds on radar last evening. A dense liftoff of nocturnal migrants is indicated at radar sites across the northeastern United States. Rain showers can be seen in Virginia. (NOAA/National Weather Service image)

Today’s arrivals—Neotropical migrants found in a streamside thicket in the Lower Susquehanna River Watershed this morning…

Red-eyed Vireos nest in forests throughout the lower Susquehanna valley.

The Northern Waterthrush is a regularly occurring migrant that can be found in vegetated wetlands and along the backwaters of streams and rivers. Despite its drab appearance, it is classified as one of our Neotropical warbler species.

The adult male American Redstart is unlike any other eastern warbler. It is easily recognized. Along the lower Susquehanna, redstarts nest in the dense understory of damp forests.

The first-spring male American Redstart is similar to the female, but usually shows black markings beginning to develop on the breast and face. It is an energetic singer.

In its strikingly colorful plumage, the Magnolia Warbler is a classic Neotropical bird. Locally, it is a regular migrant.

The Wilson’s Warbler (Cardellina pusilla) forages in lowland thickets during its migratory stopovers. Riparian buffers along streams can provide critical habitat for this and other transient species.

Baltimore Orioles continue to trickle in, creating squabbles when they enter nesting territories established by birds that arrived earlier in the month.

September 10, 2017September 4, 2019

Yellowlegs for Breakfast

A few nocturnal migrants flew through the moonlit night to arrive at Conewago Falls for a sunrise showing this morning. A dozen warblers were in the treetops and a Wood Thrush (Hylocichla mustelina) chattered away in the understory of the Riparian Woodlands. Three species of shorebirds were in the falls and on the Pothole Rocks: Least Sandpiper (Calidris minutilla), Lesser Yellowlegs (Tringa flavipes), and Greater Yellowlegs (Tringa melanoleuca).

A Greater Yellowlegs (right) and two Lesser Yellowlegs sandpipers dropped by for breakfast.

The diurnal migration was highlighted by a Merlin (Falco columbarius), an Osprey, and a Bald Eagle, each flying down the river. Most of the other birds in the falls seemed content to linger and feed. There’s no need to hurry folks, only trouble lurks down there in paradise at the moment.

A light to moderate flight of nocturnal migrants in the eastern United States is displayed on NOAA National Weather Service NEXRAD radar at 4:58 AM EDT. The eye of Hurricane Irma can be seen approaching the Florida Keys. (NOAA/National Weather Service image)

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September 4, 2017September 4, 2019

Suggestive Selling

A Baltimore Oriole (Icterus galbula) glowed in the first sunlight of the day as it began illuminating the treetops. I’m not certain of the cause, but I often have the urge to dig into a bowl of orange sherbet after seeing one these magnificent blackbirds. That’s right, in the Americas, orioles and blackbirds are members of the same family, Icteridae. Look at blackbirds more carefully, you might see the resemblance.

Sunshine at dawn and migrating warblers were again active in the foliage. Eight species were identified today. Off to the tropics they go. To the land of palm and citrus, yes citrus…limes, lemons, grapefruits, and oranges.

The Ruby-throated Hummingbirds (Archilochus colubris) are on the way toward the gulf states, then on to Central and South America. Five dashed by the rocky lookout in the falls this morning. Remember, keep your feeders clean, wash and rinse all the parts, and refill them with a fresh batch of “nectar”, four or five parts water to one part sugar. Repeating this process daily during hot weather should keep contamination from overtaking your feeder. It’s not a bad idea to rotate two feeders. Have one cleaned, rinsed, and air drying while the second is filled and in use at your feeding station, then just swap them around. Your equipment will be just as clean as it is at the sanitary dairy…you know, where they make sherbet.

The first of the season Caspian Terns (Hydroprogne caspia), giant freshwater versions of the terns you see at the seashore, passed through the falls late this morning. Their bills are blood-red, not orange like the more familiar terns on the coast. They’re stunning.

Ring-billed Gulls (Larus delawarensis) have been at the falls for several weeks. Total numbers and the composition of the age groups in the flock change over the days, so birds appear to be trickling through and are then replaced by others coming south. The big push of southbound migrants for this and many other species that winter locally in the Mid-Atlantic region and in the southern United States is still more than a month away. There are still plenty more birds to come after the hours of daylight are reduced and the temperatures take a dip.

A Ring-billed Gull on the lookout for a morning snack. They’ll eat almost anything and do a good job of keeping the river picked clean of the remains of animals that have met misfortune. They’ll linger around landfills, hydroelectric dams, and fast-food restaurant parking lots through the winter.

Turkey Vultures *(Cathartes aura)* are common around the falls due to the abundance of carrion in the vicinity and because of the strong thermal updrafts of air over the sun-heated Pothole Rocks. These rising currents provide lift for circling vultures. We would expect migrating birds of a number of species will also take advantage of these thermals to gain altitude and extend the distance of their glides.

Some migrating butterflies were counted today. Cloudless Sulphurs, more of a vagrant than a migrant, and, of course, Monarchs. I’ll bet you know the Monarch, it’s black and orange. How can you miss them, colored orange.

That’s it, that’s all for now, I bid you adieu…I’m going to have a dip of orange sherbet, or two.