Pennsylvania Game News - January 2021 - 63

50 shrikes in 29 counties. The largest
occurred the winter of 1999-2000, when
there were 137 shrikes reported in 47
counties.
Paul Hess wrote a comprehensive
article for Pennsylvania Birds on the
1999-2000 irruption. It began with the
sighting of two northern shrikes on Oct.
24 in Erie County, which Hess described
as " the state's most regular shrike location,
even in non-invasive years. " By November, after the first strong cold front, shrikes
were being reported statewide. Thirty
were counted on CBCs in December and
early January, and shrike sightings continued until early March. Berks County
posted the highest number of sightings
with 12.
Because there are few accounts of
shrike ecology in North America, Hess
summarized three notable features during
the 1999-2000 irruption.
First, 53 percent of shrikes were
adults. Second, only 20 percent - mostly
adults - held territories; the rest wandered, responding to food and weather
conditions. Third, they primarily hunted
songbirds at birdfeeders, because meadow
voles were scarce that year throughout
the state.
Pennsylvania has had two more irruptions since, according to Greg Grove, who
started the WRS in 2000. In 2007-08, 80
shrikes were reported in 39 counties. That
was followed by a smaller irruption in
2011-12, with 44 shrikes in 27 counties.
Northern shrikes start returning north
from Pennsylvania in late February or
early March. While some might pair up on
winter territories, most courtship chasing
and aggressive displays by males toward
females occurs on their breeding grounds.
Both sexes also sing either two-phrase,
JANUARY 2021	

thrasher-like imitative songs of nearby
bird species or sweet warbles and harsh
screeches.
The male feeds the female during late
courtship, nest-building, laying, incubation and the early-nestling period. The
female chooses the nesting site in late
April or early May in shrubs and trees,
often willows and spruces. She places the
nest in a fork of a branch near the trunk,
usually 8 feet or more from the ground.
She also brings most of the nesting
materials, but is aided by the male. The
nest is a large, deep, bulky cup filled with
ptarmigan feathers, animal hair and dried
moss, and lined with grasses and sedges.
The nest holds four to nine grayish or
greenish-white eggs, spotted heavily with
brown, which the female incubates 14 to
21 days while the male is busy feeding
her and defending a substantial hunting
territory, as well as their nesting territory,
which comprises several acres. The male
hunts mostly for grasshoppers, beetles,
bumblebees, insect larvae and spiders.
The offspring spend 18 to 20 days as
nestlings and another several weeks as
fledglings, being fed by their parents and
taught how to hunt.
By mid-summer, the fledglings are
on their own, and sometimes the siblings
stay together and join other broods of
immatures as they continue to hone their
hunting skills.
By mid-September, these groups disperse and individually move along river
corridors out of the boreal forest into open
country. They also follow ridgelines like
small hawks do, flying just above the
treetops as they head south for the winter.
Because seeing a northern shrike here
in winter is a rare privilege, I don't expect
to see one hovering over our First Field
this winter. But our state is overdue for
another northern shrike irruption.
63
Pennsylvania Game News - January 2021

Table of Contents for the Digital Edition of Pennsylvania Game News - January 2021
