Date: 7/18/26 9:30 am From: Nick Bolgiano <nickbolgiano...> Subject: PA Breeding Bird Atlas Indicates Some Large Distributional Shifts Northward
The email summarizes personal observations and atlas maps and is the third
of three such summaries that I have been thinking of.
At nearly the halfway point in the six-year third PA Breeding Bird Atlas,
large changes are evident for several species since the second atlas two
decades ago. I discuss here northward shifts in distributions, either
northern species withdrawing to the north or southern species expanding to
the north. The expansion of southern species has been happening for many
decades, but the withdrawals of northern species is newer and especially
noticeable.
My on-the-ground atlas experience is from Sproul State Forest north of Snow
Shoe and the area in and around Black Moshannon State Park. There, I
covered 30 atlas blocks there during the second atlas and to date have 17
atlas blocks in the third atlas. Plus, I have run two Breeding Bird Survey
routes in Sproul State Forest since 2002.
Use the below-linked atlas species map website to view current PA atlas
distributions. For the four species that I concentrate on, I include a
picture of their distribution from the second atlas book.
The two species for which I have seen the most noticeable changes are
Purple Finch and Yellow-rumped Warbler. I have also seen retractions for
Winter Wren and Hermit Thrush. The Hermit Thrush changes may be more
dramatic in Rothrock State Forest, where they have inhabited the highest
elevations and so disappearances are particularly noticeable. I haven’t
seen much change for Magnolia and Blackburnian Warblers, which are more
abundant in the higher elevation areas in Sproul and Black Moshannon and
are closely connected to conifer patches.
*Purple Finch (PUFI)*. During the second atlas, Purple Finch was found
throughout the higher elevations of the Allegheny Plateau, with the point
count densities highest in the northwestern and northcentral parts of PA
(see attached map). There has been a shift in the third atlas, with Purple
Finch being found in more atlas blocks in northeastern PA. I have recorded
it 16 times in Sproul and Black Moshannon during the third atlas, thus not
many, but more frequently in my several blocks in NE PA.
In the last several decades, it has been discovered that Purple Finch is a
spruce budworm finch in the boreal forest, similar to Evening Grosbeaks.
There has been a spruce budworm infestation in eastern Quebec since 2013
and the highest concentrations of Purple Finches during the PA Christmas
Bird Count are in eastern PA, as if they are moving south from an area of
high concentration in boreal Canada. I wonder if someday we will find that
the distribution of breeding Purple Finches in the northeast U.S. is
related to the overall distribution of Purple Finches in boreal Canada.
*Yellow-rumped Warbler (YRWA)*. During the second atlas, Yellow-rumped
Warbler was found at higher elevations of the Allegheny Plateau across the
state (see attached map). But their third atlas distribution has changed
dramatically from the second. There has been a small cluster in Sproul, a
cluster at North Mt where Doug Gross and colleagues have been working, and
a loose cluster in the Poconos. A few have been found at Black Moshannon.
In Sproul, I find them mainly in white pine and tamarack groves, some of
which have been planted by the Bureau of Forestry. I have recorded it 28
times during this atlas at Sproul and Black Moshannon, so some degree of
success. But I have only had moderate success at going back to the same
place and recording again seven or more days apart.
*Hermit Thrush (HETH)*. In the second atlas, Hermit Thrush was also found
across the higher elevations of PA, including in Rothrock and Bald Eagle
SFs (see attached map). I still hear Hermit Thrushes fairly often in Sproul
and Black Moshannon, but less frequently in Rothrock. Andy Wilson and one
of his studies did a study of how more northern PA breeding birds have
changed in the Breeding Bird Survey and they found the largest change in
Hermit Thrushes, as they already tend to be found at the highest elevations
and so that is a logical place for them to vacate, especially where Eastern
hemlocks are affected by hemlock wooly adelgid. This was a topic for a
presentation at the State College Bird Club several years ago. Andy and his
students will also be working to seen how these more northern species
change between atlases.
*Southern Species Expanding Northward*
I have encountered more Red-bellied Woodpeckers and Tufted Titmice in
Sproul during this atlas than during the second atlas, but these trends
have been gradual. Tufted Titmice have been more noticeable in the Beech
Creek drainage; elsewhere I don’t find many in Sproul.
*Hooded Warbler (HOWA)*. During the second atlas, Hooded Warbler was common
much of western PA and in large patches of central and eastern PA (see
attached map). In the third atlas, they have spread into parts of northern
and northeastern PA. The Pennsylvania Game News recently included an
article about Hooded Warbler by Ronald Mumme from Allegheny College in NW
PA, who has studied this species over a long time and is lead author of the
Birds of the World account for Hooded Warblers. In his Game News article,
Ralph thought that the Hooded Warbler expansion in PA was near an end, but
that is not true in Sproul.
This is the one species that I find especially interesting because they
didn’t occur in Sproul during the second atlas except at lower elevations
along the West Branch of the Susquehanna. Now, it is especially noticeable
when I hear one singing. I have recorded it 26 times during the third atlas
in Sproul, mostly finding in or near valleys that logically lead from
places where they have been established at lower elevations. One aspect
that I find interesting is that I only occasionally find them singing at
the same place in Sproul seven or more days apart, as if the male cannot
quickly find a mate and so moves around prospecting. When I first started
birding in the Rothrock area during the 1980s, Hooded Warblers were already
established in areas with lots of mountain laurel and they have multiplied
several-fold since then. Because of abundant mountain laurel, I expect that
Hooded Warbler expansion in Sproul and Black Moshannon will be similar to
what has happened in Rothrock and Bald Eagle SFs over many decades.
