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.
