During this foggy, dreary week, if you happened to visit a parcel of land that included even a small patch of brushy growth here in the Lower Susquehanna River Watershed, you likely weren’t alone. Among the migrating songbirds grounded by the inclement weather were an abundance of these thicket-dwelling warblers—a species aptly named the Common Yellowthroat.
A Common Yellowthroat, on an extended layover due to flight cancellations imposed by this week’s moisture-laden east winds, peers from the dense cover of a tangle of shrubs and thorny vines.As soon as the inclement weather moves out, this adult male Common Yellowthroat and other avian migrants will resume their southbound journey. Until then, he has plenty of time to scrounge around in the low-growing vegetation for insects and other fare to replenish the energy stores needed for the trip.
Get ready. The sun will show its glow in just a couple of days and when it does, bottled-up birds are going to make a run for it. Do plan to get out and have a look later this week.
We have at last reached the autumnal equinox, a day when everything is even stephen, equal time both with and without sunlight. Southbound birds like this juvenile Scarlet Tanager can now freely be called “fall migrants”, even though the majority of tanagers and other Neotropical species departed for warmer climes earlier this month, technically during the summer season.
For the past several weeks, we’ve given you a look at the fallout of Neotropical songbirds on mornings following significant nocturnal flights of southbound migrants. Now let’s examine the diurnal (daytime) flights that have developed in recent days over parts of the lower Susquehanna basin and adjacent regions.
For those observing diurnal migrants, particularly at raptor-counting stations, the third week of September is prime time for large flights of tropics-bound Broad-winged Hawks. Winds from easterly directions during this year’s movements kept the greatest concentrations of these birds in the Ridge and Valley Province and upper areas of the Piedmont as they transited our region along a southwesterly heading. Counts topped 1,000 birds or more on at least one day at each of these lookouts during the past seven days. Meanwhile at hawk watches along the Piedmont/Atlantic Coastal Plain border, where flights topped 10,000 or more birds on the best days last fall, observers struggled to see 100 Broad-winged Hawks in a single day.
Dozens of migrating Broad-winged Hawks during a morning liftoff to the north of Blue Mountain.
Among the challenges counters faced while enumerating migratory Broad-winged Hawks this week was the often clear blue skies, a glaring sun, and the high altitude at which these raptors fly during the mid-day hours.
Large numbers of Broad-winged Hawks climbing on a thermal updraft to gain altitude can become increasingly difficult to spot in a clear blue sky.Higher and higher they go until they practically disappear from view.Cloud cover can help make locating really high-flying birds a bit easier, but they can sometimes climb into the lower portion of the cloud and vanish.
Another factor complicating the hawk counters’ tasks this week, particularly west of the Susquehanna River, was the widespread presence of another group of diurnal fliers.
Was it the migratory Blue Jays that are beginning to move through the area? No.Was it the increasing numbers of Sharp-shinned Hawks and other raptors? No.So what was it that complicated the hawkwatchers’ efforts to find high-flying Broad-winged Hawks during this week’s flights?Is it a bird? Is it a plane? No. And it’s nobody’s superhero either. It’s the non-native Spotted Lanternfly and it is now very numerous west of the Susquehanna and common enough to the east to make even experienced observers take a second look while scanning the skies for Broad-winged Hawks and other migrating raptors. Just how many do raptor counters have to contend with? Even where these invasive insects have become less populous in the lower Susquehanna valley, hundreds still fill the skies above forest clearings around hawk-counting stations including Waggoner’s Gap, Second Mountain, and Rocky Ridge County Park.Spotted Lanternfly populations explode with great vigor as they colonize areas with plenty of tender new growth on native, non-native, and cultivated shrubs, trees, and vines. Earlier this week, National Weather Service Doppler Radar in Pittsburgh, Pennsylvania, captured enormous mid-afternoon flights of Spotted Lanternflies in recently invaded areas of southwestern Pennsylvania and eastern Ohio. (NOAA/National Weather Service Doppler Radar image)A base velocity image consisting primarily of Spotted Lanternflies in southwestern Pennsylvania and eastern Ohio. (NOAA/National Weather Service Doppler Radar image)
As the Broad-winged Hawk migration draws to a close during the coming ten days, the occurrence of the one dozen other migratory diurnal raptors will be on the upswing. They generally fly at lower altitudes, often relying upon wind updrafts on the ridges for lift instead of high-rising thermal updrafts. They therefore present better observation opportunities for visitors at hawk watch lookouts and are less frequently confused with high-flying Spotted Lanternflies.
A Merlin seen earlier this week migrating through the Lower Susquehanna River Watershed. The numbers of migrating Merlins and other falcons will peak sometime in coming weeks.
Among the Green Frogs in the ponds at susquehannawildlife.net headquarters, a specific recessive allele is present among the population of these native amphibians. On occasions when male and female carriers of this particular recessive allele get together to produce offspring, about one quarter of the progeny will receive a copy of this mutated version of a gene from each parent. The rare recipient of this pair of recessive alleles that happens to survive the process of hatching from its egg and metamorphosing through the tadpole stage to adulthood will reveal the uncommon appearance of an amphibian with the condition resulting from this inheritance—axanthism.
Axanthic Green Frogs and other amphibians do not produce yellow pigment, therefore the normally yellow surfaces of their bodies appear white, the green surfaces blue. Axanthism is expressed only in individuals possessing a pair of specific recessive alleles for a gene that affects the cells that produce the yellow pigment. For the trait to be expressed, a frog must receive one copy of the recessive allele from each parent.The last axanthic Green Frog we saw in the headquarters ponds was this male (seen here with a typical male Green Frog) found back in July, 2008. Green Frogs that receive two copies of a dominant allele or a copy of a dominant and a recessive allele from their parents will not express the recessive trait for the axanthism gene. Making observation of cases of axanthism even rarer is the fact that blue coloration can make these frogs exceptionally susceptible to predation. Few live long enough to reproduce and thus increase the occurrence of the mutation in a population of frogs*. This cyanic individual was present during a time when “outdoor” Domestic Cats were killing frogs to take home to their misguided humans. After this brief sighting and single photograph, this blue Green Frog was never seen again.
*The incidence of axanthic frogs can increase when a blue parent, which has a pair of the recessive alleles and is therefore said to be homozygous recessive, mates with a typical-looking frog that carries both a dominant and a recessive allele for the axanthism gene and is therefore said to be heterozygous. Approximately 50% of the young from this pairing will express axanthism. By comparison, a pair of frogs that are both heterozygous will produce 25% axanthic young, and a pair of frogs that are both blue (homozygous) will yield 100% axanthic young. A pair of frogs that includes an individual that is herterozygous and a mate that is homozygous dominant for the gene will produce no axanthic frogs, but 50% of the young will be carriers of the recessive allele. A pair of homozygous dominant frogs produces no axanthic young and no carriers of the recessive allele.
It’s a sign that things are about to change. As the Neotropical warbler migration reaches its climax, other small songbirds like this Ruby-crowned Kinglet are beginning to make their southbound movements through the lower Susquehanna valley. For a kinglet, the autumn journey is greatly abbreviated compared to that of the Neotropical species. While the warblers and their traveling companions including vireos and flycatchers are primarily headed to the tropical climate zone for winter, kinglets spend the cold season in the temperate zone, an area encompassing most of the the continental United States and southern Canada. These tiny birds feed mostly on small invertebrates which, particularly during the winter months, they find in spaces among the bark of mature trees.
Yesterday morning’s fallout of hundreds of nocturnally migrating birds was followed overnight by the influx of one hundred or more new arrivals atop Second Mountain in Lebanon County, Pennsylvania. Visitors to the forest clearing used as a hawk watch lookout were treated to the antics of these colorful Neotropical species and more…
These night-flying warblers, vireos, and flycatchers did again provide a thrilling show during the hours after sunrise, but today’s rarity passed through among the hundreds of migrating diurnal raptors—the tropics-bound Broad-winged Hawks—that made their way down the ridges of the lower Susquehanna valley this afternoon.
A “kettle” of Broad-winged Hawks climbing on a thermal updraft above Second Mountain Hawk Watch.After gaining altitude, Broad-winged Hawks glide away toward the southwest in search of the next thermal updraft upon which they will rise to continue their journey to Texas, Mexico, and beyond. Over three hundred of these raptors were counted as they passed the Second Mountain lookout today.Another “kettling” flock of migrating Broad-winged Hawks above Second Mountain.A closer look reveals something unusual. While the Broad-winged Hawk at the bottom center of the image displays the typical light-morph plumage, the bird in the upper left appears to be a dark-morph Broad-winged Hawk, a rarity in the eastern United States.A zoomed-in view of the probable dark-morph Broad-winged Hawk seen over Second Mountain this afternoon. Populations of these variants nest in areas of central and western Canada.
The peak of the autumn Broad-winged Hawk migration will likely occur during the coming two weeks with many counting stations tallying more than one thousand birds on the best of days. Visit one of these prominent lookout points so that you too can witness this amazing spectacle. Click the “Hawkwatcher’s Helper: Identifying Bald Eagles and other Diurnal Raptors” tab at the top of this page to find a hawk watch near you!
Bathed in glowing sunshine, a very large fallout of migrating Neotropical songbirds enlivened the forest edge atop Second Mountain in northern Lebanon County, Pennsylvania, this morning. While last night’s flight was widespread beneath a dome of atmospheric high pressure covering the Mid-Atlantic States, this is a look at some of the 500 -1,000 migrants observed feeding on insects and other natural foods at just this single location.
As the composition of the nightly flights begins to transition to species that start their migration later in the season, numbers of birds like the Blackpoll Warbler (top) are beginning to rival those of the heretofore very common Black-throated Green Warbler (bottom).A Blackpoll Warbler.The Bay-breasted Warbler, another common species found among the fallout flock.The Tennessee Warbler was today’s most abundant migrant with at least 200 birds seen moving among the other species.A newly arrived Tennessee Warbler at sunrise.A Tennessee Warbler snatches breakfast.The Magnolia Warbler was another common find among today’s migrants.A Magnolia Warbler.A Nashville Warbler among tangles of Mile-a-minute Weed.A Nashville Warbler.Black-throated Blue Warbler.An adult male Black-throated Blue Warbler.An acrobatic Northern Parula.Blackburnian Warblers continue their southerly trek.An American Redstart.A Chestnut-sided Warbler feeding on Mile-a-minute Weed berries.A Cape May Warbler.A handsome adult male Cape May Warbler.A Swainson’s Thrush.Scarlet Tanagers continue to work their way south through the Lower Susquehanna River Watershed.A composite image of an uncommon find, a large-headed Olive-sided Flycatcher seen perched atop a dead tree snag.A brief encounter with a Philadelphia Vireo, another uncommon species.A Blue-headed Vireo, typically the last of its genus to move south in the fall, put in a welcome appearance among the hundreds of migrants.A favorite diurnal migrant, the Ruby-throated Hummingbird, was seen feeding on flowers that grew from the remains of garden waste dumped illegally along the mountain road last autumn.
Many of the observers at the Second Mountain Hawk Watch commented that this morning’s fallout was by far the best they had seen anywhere in the region during recent years. Others believed it to be the best they had ever seen. It was indeed less like a “wave” of migrants and more like a “tsunami”. Choosing a good viewing location and being there at the right time can improve your chances of seeing a spectacle like this. The good news is, it looks like another big flight is currently underway, so finding a forest edge on a ridgetop or along a utility right-of-way just might pay off for you early tomorrow morning.
Nocturnal migrating birds, a southwest-bound flight down the ridges of central Pennsylvania as indicated by Doppler radar between 10:30 and 11:30 PM EDT on September 11, 2024. (NOAA/National Weather Service image)
Clear, cool nights have provided ideal flight conditions for nocturnal Neotropical migrants and other southbound birds throughout the week. Fix yourself a drink and a little snack, then sit down and enjoy this set of photographs that includes just some of the species we found during sunrise feeding frenzies atop several of the Lower Susquehanna River Watershed’s ridges. Hurry up, because here they come…
A Black-throated Green Warbler.The Black-throated Green Warbler was perhaps the most frequently identified treetop warbler during the most recent four mornings.A Black-throated Green Warbler with a unique variation in the crown plumage.The Blackburnian Warbler was another plentiful species.Cape May Warblers have an affinity for conifers like this Eastern White Pine.But when traveling in mixed flocks with other migrants, Cape May Warblers can also be found feeding in the crown foliage of deciduous trees.This adult Tennessee Warbler appears to be adorned in a very worn set of plumage……and its traveling companion looks like it’s overdue for a new set of feathers as well.Like the Tennessee Warbler, the Nashville Warbler was common among mixed flocks.A Nashville Warbler atop a Black Cherry.This Chestnut-sided Warbler was one of several found among the more common species of migrants.A Chestnut-sided Warbler.We were lucky enough to spot this male Chestnut-sided Warbler sporting his namesake flank feathers.A Black-and-white Warbler uses its nuthatch-like feeding behavior to search the tree bark for edible invertebrates.To see the Common Yellowthroat, one must cease looking upward into the high canopy and instead give the aching neck a rest by peering into the low vegetation at the forest edge.While checking the low growth, keep an eye open for other migrants among the shrubs and tangles. This Magnolia Warbler glows in the rays of a rising sun as it searches for a meal after a long night of travel.Here we found a perky little House Wren.Back in the middle and upper reaches of the trees, we find what has been by far the most numerous of the flycatchers seen during our visits to fallout sunrises. Eastern Wood-Pewees are appearing in very good numbers and can be seen quarreling and battling for hunting perches from which they are ambushing flying insects.An Eastern Wood-Pewee fiercely defending its hunting perch.An Eastern Wood-Pewee.The numbers of migrating Least Flycatchers and other members of the genus Empidonax may be reaching their seasonal peak this week.Scarlet Tanagers are currently a common find following nocturnal flights.A Scarlet Tanager peers down from the top of a Red Maple.Did you hear a loud squeak in the treetops? It could be a southbound Rose-breasted Grosbeak stopping by for the day.A Rose-breasted Grosbeak in a dead tree snag.The Neotropical thrushes are beginning to move south now as well. We found this newly arrived Swainson’s Thrush at Rocky Ridge County Park in York County during sunrise this morning.Not surprisingly, the Red-eyed Vireo is one of the most numerous of the migrants seen feeding in the deciduous canopy following a nocturnal flight event. It’s not at all unusual to see dozens filing the trees around a ridgetop overlook or along a forest edge. Be certain to check these congregations carefully, especially the groups of birds feeding in the lower branches of tall timber or in the tops of smaller trees. This week we found……several hungry Yellow-throated Vireos arriving after nocturnal flights,……and a Philadelphia Vireo (Vireo philadelphicus) at the hawkwatch at Rocky Ridge County Park in York County.Though not a Neotropical migrant, the easier-heard-than-seen Red-breasted Nuthatch is beginning to wander south into the lower Susquehanna region. Most of these birds will eventually continue on to the pine forests of the southern United States for winter, but a few could remain to become seasonal visitors at feeding stations.Ruby-throated Hummingbirds are on the move; their migration to the tropics is well underway and nearing its peak. Ruby-throats are diurnal migrants that do a majority of their flying during the hours of daylight. The notable exception: the nighttime portion of the long southbound flight some of the birds make to cross the Gulf of Mexico.The Red-headed Woodpecker is another diurnal migrant. This denizen of temperate climates is currently beginning to move to its wintering grounds, an area that extends from the latitudes of the lower Susquehanna south to the Gulf of Mexico and central Texas.A juvenile Red-headed Woodpecker during a brief pit stop.The flights of roving bands of masked Cedar Waxwings continue. Their numbers appear to be an improvement over those of 2023.At regional hawk-counting stations, observers are seeing more Broad-winged Hawks and other species beginning to move through.The frequency of Broad-winged Hawks passing the lookouts one at a time is giving way to the occurrence of larger and larger “kettling” groups that search out thermal updrafts to save energy while migrating. By mid-September each of these “kettles” can include one hundred birds or more. On the peak days, the daily Broad-winged Hawk totals can reach one thousand or more.A Broad-winged Hawk soaring to gain lift from a thermal updraft above a hawkwatch lookout.
The migration is by no means over; it has only just begun. So plan to visit a local hawkwatch or other suitable ridgetop in coming weeks. Arrive early (between 7 and 8 AM) to catch a glimpse of a nocturnal migrant fallout, then stay through the day to see the hundreds, maybe even thousands, of Broad-winged Hawks and other diurnal raptors that will pass by. It’s an experience you won’t forget.
A Broad-winged Hawk gliding away to the southwest.
Be certain to click the “Birds” tab at the top of this page for a photo guide to the species you’re likely to see passing south through the lower Susquehanna valley in coming months. And don’t forget to click the “Hawkwatcher’s Helper: Identifying Bald Eagles and other Diurnal Raptors” tab to find a hawk-counting station near you.
More birds are on the way. Here’s a look at this evening’s liftoff of nocturnal migrants detected by National Weather Service Radar in State College, Pennsylvania. (NOAA/National Weather Service Doppler Radar image)
