Late May Action in the Forest

Here’s a short preview of some of the finds you can expect during an outing in the Lower Susquehanna River Watershed’s forests this week…

Mountain Laurel
The Mountain Laurel, designated as Pennsylvania’s state flower, is now in bloom.
Mountain Laurel Flower Buds
The buds of the Mountain Laurel remind us of a sugary frosting freshly squeezed from a baker’s pastry bag.
Mountain Laurel Flowers
The flowers of the Mountain Laurel, an evergreen understory shrub, invite pollinators to stop by for a sweet treat.
Little Wood-Satyr
Little Wood-Satyrs (Megisto cymela) are patrolling forest edges looking for mates and, to host their eggs and larvae, the stands of grasses they find most suitable.
Zabulon Skipper
Many of the species of small butterflies we call skippers are now active. The Zabulon Skipper can be found patrolling grassy forest edges, particularly near streams, ponds, and wetlands.
Red-spotted Purple
Among the showiest of our butterflies, the Red-spotted Purple (Limenitis arthemis astyanax) is seen here on the leaves of a Black Cherry, its favored host plant.
Red-spotted Purple
Another red-spotted Purple seen picking up minerals from a dried up puddle depression on a gravel road.
Susquehanna Riverlands State Park
Butterfly observers will do well to pay a visit to the new Susquehanna Riverlands State Park on Furnace Road north of Hellam in York County, Pennsylvania.
Trail to Schull's Rock Overlook
Upon arrival at Susquehanna Riverlands, drive back the gravel road for about a mile to the parking area at the edge of the agricultural field.  Then, hike the trail through the woods and farm hedgerow to the Schull’s Rock overlook on the river.  In the forests along this route, the understory is dominated by colonial stands of Common Pawpaw trees.
Common Pawpaw
Along the lookout trail to Schull’s Rock, the Common Pawpaws’ large leaves help them to shade out potentially fast-growing competition.  In proper growing situations, pawpaws develop clonal suckers that mature over time to create colonial stands of a single genetic plant.
Common Pawpaw understory.
A Common Pawpaw understory along the approach to Schull’s Rock.
Common Pawpaw
A colonial stand of Common Pawpaw along the trail leading to Schull’s Rock.
Zebra Swallowtail
During our recent visit to Schull’s Rock, dozens of Zebra Swallowtails were seen along the trail, many in the vicinity of their sole host plant, the Common Pawpaw.  But even more were observed along the edges of the fields and woods where nectar sources like this Multiflora Rose were being visited by numbers of butterflies we normally see only among abundant species like Cabbage Whites.  Absolutely amazing!
Scull's Rock Overlook
And the view of the Susquehanna and the Shock’s Mills railroad bridge at the mouth of Codorus Creek is pretty good too!
Common Pawpaw and Hooded Warbler
You can look for colonial stands of Common Pawpaw at other parks and preserves along the lower Susquehanna as well.  Birds like this Hooded Warbler can sometimes be found among them in mature riparian forests along the steep slopes of the river gorge.
Common Pawpaw and Baltimore Oriole
A Baltimore Oriole in a Common Pawpaw along a forest edge.
Blackpoll Warbler
Meanwhile in the treetops, the spring thrust of Neotropical migrants is drawing to a close.  The Blackpoll Warbler is typically one of the last to transit the lower Susquehanna valley on its way to northern coniferous forests for summer.  They’ve had an unusually protracted movement through the region this spring, the earliest individuals reported during late April.  Though very difficult to see in the canopy of the mature trees where it feeds and sings, hearing one is often a benchmark for senior birders each spring.  Older observers have often said of the Blackpoll Warbler’s high-pitched song, a rapid series of insect-like staccato “tseet” notes, that it was the first they could no longer detect as their ears started losing sensitivity.
American Redstart
In many tracts along the lower Susquehanna this spring, the American Redstart is turning out to be the most common nesting warbler.  Conditions favoring their reproductive success in recent cycles, as well as good survival rates during their migrations and stays on wintering grounds, have filled many lowland forests with redstart songs in 2025.  Is this the start of a trend or just an exceptionally good year?  Time will tell.
Rose-breasted Grosbeak
Yet one more reason for a stroll in local forests this week is the chance to see and hear the Rose-breasted Grosbeak.  Look for these Neotropical relatives of the cardinal nesting on territories in mature stands of deciduous trees like this Yellow Poplar, a species also known as the Tuliptree.
They spend nearly all their time among the canopy foliage of the largest timber…
Rose-breasted Grosbeak
…but pause frequently to repeat a song often described as something akin to that which might be performed by a robin subjected to voice lessons.  The Rose-breasted Grosbeak is certainly a bird worth seeing and hearing.

Singing in the Rain

Neotropical birds are fairly well acquainted with repetitive periods of thundershowers.  With that in mind, we decided not to waste this stormy Tuesday by remaining indoors.

Thundershower
Periods of rain need not put a damper on a day outdoors observing birds that wintered in a rain forest or other tropical environment.
Utility Right-of-way with Successional Habitat
We hiked this utility right-of-way to the north of a heavy thunderstorm and found plenty of activity in the shrubby successional habitat there.
Indigo Bunting
Rain or shine, male Indigo Buntings were busy singing.  All this exuberance is intended not only to establish and defend a nesting territory…
Indigo Bunting
…but to attract the attention of a mate as well.
Blue-winged Warbler
Prior to the implementation of the intensive manicuring practices we see currently applied to most utility right-of-ways, shrubby thickets filled miles of these linear corridors to create a webbed network of early successional growth throughout the lower Susquehanna valley.  Loss of this specialized habitat has led to the almost total elimination of the formerly common Blue-winged Warbler as a breeding species here.
Blue-winged Warbler
We found three male Blue-winged Warblers singing on territories in this bushy clearing where electric transmission lines pass over Third/Stony Mountain on State Game Lands 211.
Blue-winged Warbler
Their presence at this site is testament to the importance of maintaining corridors of quality successional habitat in the landscape.
Blue-winged Warbler
The Blue-winged Warbler is a Neotropical migrant with an easy-to-learn song.  It’s a very simple, buzzy sounding “beeee-bzzz”.
Prairie Warbler
Another Neotropical species that nests in successional thickets is the Prairie Warbler (Setophaga discolor), seen here during one of this morning’s downpours.
Prairie Warbler
The Prairie Warbler can sometimes be found in stands of pioneer plants like Eastern Red Cedar on sites with barren soils or those that have been subjected to wildfire.
Hooded Warbler
The Hooded Warbler is fond of wooded thickets along the edge of forested land such as those in the Third/Stony Mountain utility right-of-way.
Hooded Warbler
The presence of a Mountain Laurel thicket also enhances a forest’s ability to host breeding Hooded Warblers.

We hope you enjoyed our walk in the rain as much as we did.  If you venture out on a similar excursion, please remember this.  The majority of the wild animals around us have busy lives, particularly at this time of year.  Most don’t take a day off just because it rains—that includes ticks.

Female Deer Tick
Be certain to check yourself for ticks, especially these very small Deer Ticks (Ixodes scapularis), also known as Black-legged Ticks.  Deer Ticks are vigilantly looking for something to latch onto, even in the rain, and they can be vectors of Lyme disease.  We found this adult female as a stowaway on the editor’s neck just before heading home from today’s stroll.

Blooming in Early July: Great Rhododendron

With the gasoline and gunpowder gang’s biggest holiday of the year now upon us, wouldn’t it be nice to get away from the noise and the enduring adolescence for just a little while to see something spectacular that isn’t exploding or on fire?  Well, here’s a suggestion: head for the hills to check out the flowers of our native rhododendron, the Great Rhododendron (Rhododendron maximum), also known as Rosebay.

Great Rhododendron
The Great Rhododendron is an evergreen shrub found growing in the forest understory on slopes with consistently moist (mesic) soils.  The large, thick leaves make it easy to identify.  During really cold weather, they may droop and curl, but they still remain green and attached to the plant.

Thickets composed of our native heathers/heaths (Ericaceae) including Great Rhododendron, Mountain Laurel, and Pinxter Flower (Rhododendron periclymenoides), particularly when growing in association with Eastern Hemlock and/or Eastern White Pine, provide critical winter shelter for forest wildlife.  The flowers of native heathers/heaths attract bees and other pollinating insects and those of the deciduous Pinxter Flower, which blooms in May, are a favorite of butterflies and Ruby-throated Hummingbirds.

Pinxter Flower in bloom
A close relative of the Great Rhododendron is the Pinxter Flower, also known as the Pink Azalea.

Forests with understories that include Great Rhododendrons do not respond well to logging.  Although many Great Rhododendrons regenerate after cutting, the loss of consistent moisture levels in the soil due to the absence of a forest canopy during the sunny summertime can, over time, decimate an entire population of plants.  In addition, few rhododendrons are produced by seed, even under optimal conditions.  Great Rhododendron seeds and seedlings are very sensitive to the physical composition of forest substrate and its moisture content during both germination and growth.  A lack of humus, the damp organic matter in soil, nullifies the chances of successful recolonization of a rhododendron understory by seed.  In locations where moisture levels are adequate for their survival and regeneration after logging, impenetrable Great Rhododendron thickets will sometimes come to dominate a site.  These monocultures can, at least in the short term, cause problems for foresters by interrupting the cycle of succession and excluding the reestablishment of native trees.  In the case of forests harboring stands of Great Rhododendron, it can take a long time for a balanced ecological state to return following a disturbance as significant as logging.

Birds of Conewago Falls in the Lower Susquehanna River Watershed: Ruffed Grouse
Ruffed Grouse (Bonasa umbellus) may be particularly sensitive to the loss of winter shelter and travel lanes provided by thickets of Great Rhododendron and other members of the heather/heath family.  (Vintage 35 mm image)

In the lower Susquehanna region, the Great Rhododendron blooms from late June through the middle of July, much later than the ornamental rhododendrons and azaleas found in our gardens.   Set against a backdrop of deep green foliage, the enormous clusters of white flowers are hard to miss.

Great Rhododendron Flower Cluster
Great Rhododendrons sport an attractive blossom cluster.  The colors of the flower, especially the markings found only on the uppermost petal, guide pollinators to the stamens (male organs) and pistil (female organ).
Bumble Bee Pollinating a Great Rhododendron Flower
To this Bumble Bee (Bombus species), the yellowish spots on the uppermost petal of the Great Rhododendron may appear to be clumps of pollen and are thus an irresistible lure.  

In the Lower Susquehanna River Watershed, there are but a few remaining stands of Great Rhododendron.  One of the most extensive populations is in the Ridge and Valley Province on the north side of Second Mountain along Swatara Creek near Ravine (just off Interstate 81) in Schuylkill County, Pennsylvania.  Smaller groves are found in the Piedmont Province in the resort town of Mount Gretna in Lebanon County and in stream ravines along the lower river gorge at the Lancaster Conservancy’s Ferncliff and Wissler’s Run Preserves.  Go have a look.  You’ll be glad you did.

Great Rhododendron along Route 125 near Ravine
Great Rhododendron along Route 125 along the base of the north slope of Second Mountain north of Ravine, Schuylkill County, Pennsylvania.
Great Rhododendron along Swatara Creek
Great Rhododendrons beginning to bloom during the second week of July along Swatara Creek north of Ravine, Schuylkill County, Pennsylvania.  Note how acid mine drainage has stained the rocks in the upper reaches of this tributary of the lower Susquehanna.  Mitigation of leachate pollutants from legacy mines has facilitated the return of over two dozen species of fish to this waterway, but the telltale discoloration of the stream substrate will remain for some time.

Blooming Now in the Lower Susquehanna Region: Mountain Laurel

Mountain Laurel (Kalmia latifolia), designated as Pennsylvania’s state flower, is a native evergreen shrub of forests situated on dry rocky slopes with acidic soils.  As the common name implies, we think of it mostly as a plant of the mountainous regions—those areas of the Susquehanna watershed north of Harrisburg.  It is indeed symbolic of Appalachian forests.  But Mountain Laurel can also be found to the south of the capital city in forested highlands of the Piedmont.  There, currently, it happens to be in full bloom.  Let’s put on a pair of sturdy shoes and take a walk in the Hellam Hills of eastern York County at Rocky Ridge County Park to have a look.

The showy flower clusters of blooming Mountain Laurel are conspicuous throughout Rocky Ridge County Park right now.
Mountain Laurel flowering in the utility right-of-way south of the main parking area at Rocky Ridge…
…and to the north of the parking area at the hawk-watch platform.
Strolling a forest trail, particularly west of the utility right-of-way, can take you on a path through a thicket of flowering Mountain Laurel.
The majority of Mountain Laurels one might encounter will sport white flowers.
Others vary, exhibiting shades of spectacular pink.
Look closely and you’ll see flowers with curled filaments on some of the stamens.  When a bee or other insect makes contact, they spring into an extended position to assure pollen transfer to the visiting pollinator.
Absolutely spectacular.

Rain or shine, do get out and have a look at the blooming Mountain Laurel.