Altitudinal Range Shifts of Birds At the Southern Periphery of the Boreal Forest: 40 Years of Change In the Adirondack Mountains

Abstract

Studies of geographic range shifts in response to climate warming that use data from Christmas Bird Counts or repeated state and provincial faunal atlases are better at detecting latitudinal shifts than altitudinal shifts because the coarse geographic scale of most citizen-science survey units masks the substantial elevational variation within their boundaries. To more directly measure altitudinal range shifts of forest-breeding bird species, we repeated an altitudinal transect survey conducted 40 years ago at Whiteface Mountain in the Adirondacks, New York, USA. We conducted roadside bird surveys at dawn and dusk at seven survey stations that ranged in altitude from 500 m to 1,425 m. We found considerable interspecific variation in the movement of altitudinal ranges, but document a preponderance of uphill shifts in both upper and lower boundaries of altitudinal breeding ranges. The shift of abundance-weighted mean altitudes for 42 species detected in both survey periods was +82.8 m. These shifts are correlated with a regional trend toward warmer summers from Adirondack weather station data collected over this same time period. Upper range boundaries have shifted more than lower boundaries, resulting in novel bird communities at some elevations (e.g., we found 13 species at 1,425 m vs 7 species at this altitude in 1974), resulting in a flattening of the altitudinal gradient of species richness. At low elevations we encountered several species that were not recorded on the transect in 1974, a trend we attribute to climate warming and anthropogenic habitat change at low altitudes. Our resurvey shows that there have been substantial upward range shifts in most bird species on Whiteface Mountain in the last four decades, and provides a basis for reassessment of altitudinal range dynamics at the southern edge of the North American boreal forest in the coming decades.

Full text

The Wilson Journal of Ornithology 129(4):742–753, 2017
ALTITUDINAL RANGE SHIFTS OF BIRDS AT THE SOUTHERN PERIPHERY
OF THE BOREAL FOREST: 40 YEARS OF CHANGE IN THE ADIRONDACK
MOUNTAINS
JEREMY J. KIRCHMAN
1,2
AND ALISON E. VAN KEUREN
1
ABSTRACT.—Studies of geographic range shifts in response to climate warming that use data from Christmas Bird
Counts or repeated state and provincial faunal atlases are better at detecting latitudinal shifts than altitudinal shifts because the
coarse geographic scale of most citizen-science survey units masks the substantial elevational variation within their
boundaries. To more directly measure altitudinal range shifts of forest-breeding bird species, we repeated an altitudinal
transect survey conducted 40 years ago at Whiteface Mountain in the Adirondacks, New York, USA. We conducted roadside
bird surveys at dawn and dusk at seven survey stations that ranged in altitude from 500 m to 1,425 m. We found considerable
interspecific variation in the movement of altitudinal ranges, but document a preponderance of uphill shifts in both upper and
lower boundaries of altitudinal breeding ranges. The shift of abundance-weighted mean altitudes for 42 species detected in
both survey periods was þ82.8 m. These shifts are correlated with a regional trend toward warmer summers from Adirondack
weather station data collected over this same time period. Upper range boundaries have shifted more than lower boundaries,
resulting in novel bird communities at some elevations (e.g., we found 13 species at 1,425 m vs 7 species at this altitude in
1974), resulting in a flattening of the altitudinal gradient of species richness. At low elevations we encountered several
species that were not recorded on the transect in 1974, a trend we attribute to climate warming and anthropogenic habitat
change at low altitudes. Our resurvey shows that there have been substantial upward range shifts in most bird species on
Whiteface Mountain in the last four decades, and provides a basis for reassessment of altitudinal range dynamics at the
southern edge of the North American boreal forest in the coming decades. Received 23 September 2016. Accepted 6 April
2017.
Key words: Adirondack Mountains, boreal forest, climate change, elevation gradient, range dynamics, resurvey.
The evidence for recent geographic range shifts
in response to warming climate continues to grow
as researchers examine long-term data sets col-
lected at a wide range of temporal and geographic
scales. Consistent with theoretical predictions,
animals are generally found to be moving uphill
and toward the poles in correlation with rising
average temperatures (La Sorte and Thompson
2007, Tingley et al. 2009, Freeman and Class
Freeman 2014), although counter examples are
known (Archaux 2004) and many studies find that
a subset of species do not follow the trend (Tingley
et al. 2012, DeLuca and King 2017). In fact, the
magnitude (and indeed, the direction) of responses
to increasing temperatures are known to differ
among taxonomic groups, among communities
found at different latitudes or altitudes (DeLuca
and King 2017), or in different geographic regions
(Roth et al. 2014), and among species with
differing levels of dietary breadth (Auer and King
2014). Much remains to be learned about species’
responses to climate change with respect to
altitudinal distributions, including documenting
the ways that species found in different ecogeo-
graphic regions are responding.
For birds, which are easily surveyed and for
which many citizen-science monitoring projects
exist, poleward range shifts have been documented
for eastern North American birds using data from
the Audubon Society’s Christmas Bird Counts
(CBC; La Sorte and Thompson 2007), the
American Breeding Bird Survey (BBS; Hitch and
Leberg 2007, Auer and King 2014), and repeated
breeding bird atlases (Zuckerberg et al. 2009).
Detecting altitudinal shifts with these data sets is
much harder than detecting latitudinal shifts
because of the large scale of the survey units
(BBS ¼40 km routes, CBC ¼452 km
2
circles, and
most state atlas projects ¼25 km
2
blocks). Studies
that use these data sets typically use the average
elevation of a count unit (although Auer and King
(2014) used 8 km sub-segments of BBS routes)
and miss the sometimes substantial elevational
variation within their boundaries. Studies by
Hickling et al. (2006) and Zuckerburg et al.
(2009) reported average down-hill range shifts of
2.1 m for 22 bird species censused at 20-year
intervals in the UK, and 5.2 m for 129 bird
species censused at 20-year intervals in New York
state, respectively. Both studies tracked altitudinal
1
New York State Museum, Albany, NY, USA.
2
Corresponding author e-mail:
jeremy.kirchman@nysed.gov
742

movement of species by calculating the mean
altitude of the ten highest occupied blocks from
each survey period; the survey of British birds
used a 10 km 310 km grid whereas the New York
study used a 5 km 35 km grid. Surveys conducted
at smaller scales, such as a 1 km
2
grid used by the
Italian bird atlas (Popy et al. 2010, which found a
þ7.6 m mean range shift over 11 years) and the
Swiss Biodiversity Monitoring program (Roth et
al. 2014) may be better at detecting altitudinal
shifts of birds in mountainous regions but still rely
upon averaging the altitude of survey blocks that
may span .600 m elevation (Popy et al. 2010).
The meta-analysis of range shifts conducted by
Chen et al. (2011) using data from these and other
studies found that birds generally track the
latitudinal changes observed in other taxa on
decade time scales, but were the only taxon found
to have moved predominantly down-hill, suggest-
ing that either bird ranges are shifting in latitude
but not in altitude, or that the problem of
interpreting altitudinal shifts with large scale
survey data may be especially acute for birds.
Important details of shifting altitudinal range
boundaries emerge from studies that replicate
surveys conducted at specific points along altitu-
dinal transects decades ago, such as the recent
resurveys of historical transects in the French Alps
(Archaux 2004), the Peruvian Andes (Forero-
Medida et al. 2011), New Guinea (Freeman and
Class Freeman 2014), New Hampshire (DeLuca
and King 2017), and California (Tingley et al.
2009, 2012). These studies found that altitudinal
movements at decade to century time scales varied
widely among ecogeographic regions and among
species. The diversity of responses may be a result
of different species tracking different aspects of
climate, such as temperature versus precipitation
(Tingley et al. 2012), or biotic versus abiotic
aspects of their niche (DeLuca and King 2017).
Clearly more study is needed to document actual
altitudinal movements of bird ranges in the era of
rapid climate warming.
In this study, we repeat a survey of altitudinal
ranges of birds in the Adirondack Mountains
conducted 40 years, ago by Able and Noon (1976),
and assess changes in the upper and lower range
boundaries of forest birds in the context of
regional, long-term climate data. The Adirondacks
comprise an uplifted, highly dissected dome of
Proterozoic continental shield rocks that rises up
out of the surrounding Paleozoic bedrock in
northern New York, USA (Fig. 1). Maximum
elevation of this mountain range is 1,629 m, and
there are 26 peaks with elevations .1,300 m.
Because this region is near the northern boundary
of the temperate deciduous forest biome, the
vegetation changes altitudinally from temperate
hardwoods (,300 m), to mixed conifer-northern
hardwoods (300–850 m), to spruce-fir dominated
boreal forest (850–1,450 m), to alpine tundra
(.1,450 m; Whitehead and Jackson 1990). Thus,
the Adirondacks, at 43–458N latitude, represent
an isolated southern outpost of the boreal forest
ecosystem that, at lower elevations, reaches its
southern periphery at ca. 48–508N (Fig. 1, inset).
The montane spruce-fir forests of New York and
northern New England are the southeastern
periphery of the breeding range for several boreal
forest bird species, and are therefore dispropor-
tionately important in terms of regional biodiver-
sity. Climate niche models of boreal forest bird
breeding ranges predict large shifts to the north
and west in the coming decades, leading to
extirpations in New York and New England as
populations are pinched off the tops of mountains
in the Catskills, Adirondacks, Green Mountains,
and White Mountains (Rodenhouse et al. 2008,
Ralston and Kirchman 2012). Our measurement of
altitudinal range shifts over 40 years in the
Adirondacks provides new data by which to assess
predictions from climate niche models and the
results of monitoring efforts that indicate signifi-
cant population declines for many species of
boreal forest birds (Ralston et al. 2015). We use
our resurvey data to ask the following questions:
1) Do previous assessments of altitudinal shifts
based on broader scale citizen-scientist surveys of
birds in New York reflect the true movement of
bird ranges in the Adirondack Mountains? 2) Are
altitudinal range shifts of birds consistent with
regional temperature changes during the breeding
season? 3) Do changes in the breadth of altitudinal
ranges reflect regional population trend estimates
for boreal forest bird species?
METHODS
Able and Noon (1976) conducted their bird
surveys on the north facing slope of Whiteface
Mountain on 11–12 July 1974. The route follows
743Kirchman and Van Keuren ALTITUDINAL RANGE SHIFTS

the Whiteface Mountain Veterans Memorial High-
way, also called NY State Route 432 (Fig. 1). The
site was chosen because it is a long, easily
accessible elevational gradient (over 1,000 m)
with gradual, uniform slopes in mature second
growth northern hardwood forest and virgin
spruce-fir forest with minimal disturbance. The
transect comprised survey stations at intervals of
ca. 150 m elevation that they determined by
reference to topographic maps, along vegetation
gradients that spanned three major ecotones
recognized by the turnover of tree species: 1)
replacement of sugar maple (Acer saccharum) and
beech (Fagus grandifolia) by red spruce (Picea
rubens) and yellow birch (Betula alleghaniensis),
2) disappearance of deciduous trees and increase in
balsam fir (Abies balsamea), and 3) replacement of
stunted spruce-fir forest with arctic tundra (‘tree
line’). Since the 1970s, the forests on Whiteface
have remained undisturbed except for expansion
of the ski trails on the south facing slopes for the
1980 Winter Olympics and again in the 1990s and
2000s. The width and pathway of the highway has
not changed since it was completed in 1935.
We obtained Able and Noon’s original data
sheets from Kenneth P. Able. These included
descriptions of seven survey stations (at altitudes
of 500 m, 650 m, 825 m, 975 m, 1,125 m, 1,275
m, and 1,425 m a.s.l.), tallies of individuals of each
bird species at each station, and the number of
observer hours at each stop. We resurveyed the
complete transect on 9–10 July 2013, 30 June–2
July 2014, and a subset of the stations on 2–3 June
2015. We were careful to employ the same survey
technique described in Able and Noon (1976):
Birds were censused during the 3–4 hrs of peak
FIG. 1. Topographic map of New York, showing the location of Whiteface Mountain in the Adirondack Mountians.
Inset: The range of white spruce (Picea glauca, from Little 1971) is used to show the approximate extent of the boreal forest
biome in North America.
744 THE WILSON JOURNAL OF ORNITHOLOGY Vol. 129, No. 4, December 2017

singing activity immediately following dawn each
day. At each station, we walked in different
directions counting all birds heard or seen while
moving steadily through the area along the road
and in the adjacent forest for 0.5–0.75 hrs. On 9
July 2013, 30 June and 1 July 2014, and 2 June
2015, we also surveyed subsets of the seven
stations in the 2–3 hrs prior to dusk, resulting in a
total of 5.0–6.5 observer-hours per station. On
successive days, we altered the order in which the
stations were surveyed to minimize bias because of
time of day. As in the original survey, we
opportunistically employed ‘squeaking’ and ‘pish-
ing’ to attract nearby birds, and tallied all
individuals heard and seen for all species of
woodpeckers, hummingbirds, and passerines.
We examined shifts in the altitudinal ranges of
all species detected in both survey periods two
ways. First, we used a presence-absence approach
to determine the upper and lower altitudinal
boundary of each species’ range in each time
period (1974 and 2013–15), treating a species as
present at a given altitude if one or more birds was
detected at that altitude over the course of all
surveys in that time period. We then calculated the
shift of the upper boundary as the difference, in
meters, between the highest observations for that
species in each time period, excluding species
which were found at the top of the transect in both
survey periods. Lower boundary shifts were
calculated the same way with respect to the lowest
observed individuals of each species. Second, we
estimated the abundance of each species at each
elevation as the number of birds recorded per
observer-hour, and used these data to calculate an
abundance-weighted mean elevation for each
species following Forero-Medina et al. (2011).
Range shifts were estimated as the difference in
the abundance-weighted mean elevations between
the two survey periods, excluding species that
were not detected in both survey periods (raw data
and calculations are in Supplemental Table S1).
This method accounts for differences in survey
effort between the two time periods and for shifts
in abundance of each species along its altitudinal
range, weighting more heavily those elevations
where it is found in higher numbers. Significance
of differences in weighted mean altitudes between
the two time periods was assessed with a paired,
two-tailed t-test. To test whether combining data
from more than one year in the resurvey period
biased our comparisons with the data from 1974,
we calculated weighted mean altitudes from data
gathered in 2013 and 2014 separately (years when
all stations were surveyed at least twice).
To investigate the correlation of altitudinal
range shifts with climate change over the 40-year
study period, we obtained daily surface tempera-
ture data for May, June, and July, at the Lake
Placid, NY, weather station from the National
Climate Data Center (www.ncdc.noaa.gov). We
chose the May–July period because it encompass-
es the beginning of the breeding season, when
migrant birds return and establish territories, and
the peak of the breeding season when our surveys
were conducted, but not the late summer when
young of the year have fledged and may have
dispersed beyond natal territories. This weather
station (identified as Lake Placid 2 S NY US,
GHCND:USC00304555) is located 14.5 km SSE
of the summit of Whiteface Mountain at
44.2498N, 073.9858W, 591 m elevation, and is
the closest weather station to Whiteface Mountain
for which summer temperature data were available
for the entire 40-year study period. We estimated
temporal trends in the climate data by calculating
mean daily maximum and minimum temperatures
for each summer (92 days) and the mean minimum
and maximum temperatures of the 5 coldest and
the 5 warmest days, respectively, for each summer.
We used least squares linear regression to fit trend
lines to the data and to calculate the change in
average summer temperatures over the 40-year
study period.
RESULTS
In our surveys, we detected 49 species,
including seven that were not found in 1974,
whereas Able and Noon detected 44 species,
including two that we failed to record (Table 1).
Differences in the species detected between survey
periods were greatest at the lowest two elevations
(650 m), where we found six species that were
not recorded in 1974 (Eastern Wood-Pewee,
Eastern Phoebe, Great Crested Flycatcher, Com-
mon Yellowthroat, Chipping Sparrow, and Song
Sparrow; scientific names for all species are in
Table 1). Despite finding six species at the lowest
elevations that were not detected in the 1974
survey, species richness at 500 m was higher in
745Kirchman and Van Keuren ALTITUDINAL RANGE SHIFTS

1974 (Fig. 2). This is because upward shifts in the
elevational ranges of several species resulted in the
peak of species richness shifting from 500 m in
1974 to 650 m in 2013–14 (Fig. 2). In both survey
periods, the number of species declined with
increasing elevation, but we found many more
species at the highest elevations relative to the first
survey (e.g., 13 vs. 7 at 1,425 m), resulting in a
flattening of the altitudinal gradient of species
richness.
Mean daily breeding season temperatures in the
Adirondack Mountains have increased steadily
over the last 40 years (Fig. 3), with average daily
minimum temperature increasing by 2.46 8C(y¼
0.0616x 114.00, r
2
¼0.516) and average daily
maximum temperature increasing by 1.88 8C(y¼
0.047x 71.66, r
2
¼0.267). Mean minimum and
maximum temperatures of the 5 coldest and 5
warmest days from each breeding season (not
shown) also increased over the last 40 years, but
regression lines had less positive slopes (coldest: y
¼0.0322x 67.06, warmest: y ¼0.0565x 
82.808) and lower r
2
values (coldest: r
2
¼0.121,
warmest: r
2
¼0.187) indicating that the observed
climate change over this period is not driven by
more extreme weather events. Consistent with the
predicted response to these trends toward warmer
summers, we found that bird species predominant-
ly moved up in altitude over the last 40 years at
both their upper and lower range boundaries, and
in their abundance-weighted mean altitudes (Table
1, Fig. 4). Abundance-weighted mean altitudes of
42 species detected in both survey periods were
significantly higher in 2013–15 than in 1974 (P,
0.001). The average shift was þ82.8 m, with 26
species shifting uphill versus only 11 shifting
downhill and 5 showing no shift. We found
significant shifts in the same directions and similar
FIG. 2. Species richness along the Whiteface Mountain altitudinal transect, surveyed in 1974 (gray line) and in 2013–15
(black line).
FIG. 3. Mean daily minimum and maximum breeding season (May–July) temperatures at Lake Placid, NY, over the past
40 years. Solid trend lines are least squares regressions.
746 THE WILSON JOURNAL OF ORNITHOLOGY Vol. 129, No. 4, December 2017

magnitude when the data from 2013 (þ69.6 m; P¼
0.004) and 2014 (þ87.6 m; P,0.001) are
analyzed separately.
We were able to assess the shift in the lower
elevation boundary for 23 species whose lowest
detection was at 650 m or above. Of these, 16
show some movement of the lower boundary,
including 13 that have shifted up by an average of
186.5 m, and three species that have shifted down,
each by 150 m (a single survey station). The
average movement of the lower boundary for all
23 species with lower elevation boundaries within
the altitudinal transect was þ85.9 m. We could
assess movement of the upper elevational bound-
ary in 35 species whose upper elevation boundary
fell within the altitudinal transect. Of these, 14
species showed no movement, 18 species shifted
upwards by an average of 264.3 m, and three
species shifted down in altitude, each by 150 m (a
single survey station). The average movement of
the upper boundary for all 35 species with an
upper boundary within the transect was þ123.06
m.
Only two of the seven species recorded at the
highest elevation in 1974 have up-shifted lower
boundaries (resulting in smaller altitudinal ranges),
and thus might be considered to be losing ground
on Whiteface Mountain: Blackpoll Warbler and
Yellow-rumped Warbler. Of the 42 species record-
ed in both survey periods, 12 have obtained wider
altitudinal ranges within the boundaries of the
transect, 21 have the same altitudinal range
breadth, and 9 have a narrower altitudinal range.
A paired t-test failed to reject the hypothesis that
the elevational breadth of these 42 species
(measured as the number of survey stations where
each species was recorded in each of the two time
periods) has remained the same over the 40-year
study period (P¼0.075).
DISCUSSION
Our resurvey of the altitudinal transect up
Whiteface Mountain established by Able and
Noon (1976) paints a detailed picture of changes
in the altitudinal distribution of bird species over
the past 40 years at the southern periphery of the
boreal forest biome. Boreal forest birds are poorly
monitored relative to temperate species (Ralston et
al. 2015), and North America’s best long-term
monitoring projects, the Christmas Bird Counts
and the Breeding Bird Survey, barely reach the
broad swath of the boreal forest biome that
comprises 25%of the world’s forest habitat (Wells
and Blancher 2011). None of the BBS routes in the
Adirondacks can be considered altitudinal tran-
sects, as they all follow major roads along river
valleys, and many of the routes, including those
closest to Whiteface Mountain are currently
inactive. Contrary to the finding by Zuckerburg
et al. (2009) based on data from the two New York
State Breeding Bird Atlas surveys (Anderle and
Carroll 1988, McGowan and Corwin 2008), we
find evidence for uphill movement of breeding
ranges in the majority of bird species surveyed.
The discrepancy between our results and those of
Zuckerburg et al. (2009) is likely a result of the
longer interval covered by our study (40 rather
than 20 years) and of the differing geographic
scales at which the studies were conducted; the 5 3
5 km Breeding Bird Atlas survey block that
includes the peak of Whiteface Mountain includes
terrain that spans over 1,100 m of elevation. Chen
et al.’s (2011) conclusion that birds are moving
predominantly downhill on decade time scales,
unlike every other taxon they surveyed, is
undermined by the fact that three out of the four
bird studies included in their analysis are based on
the average altitude of large survey blocks which
mask substantial altitudinal variation.
Resurveys of altitudinal transects, including
ours, reveal substantial variation among bird
species in responses to climate change (Freeman
and Class Freeman 2014, Tingley et al. 2012,
DeLuca and King 2017). Our data indicate that the
predominant pattern in the Adirondacks is one of
uphill movement of breeding ranges at all
altitudes. In contrast, DeLuca and King (2017)
found that, among bird species surveyed by 5-min
point counts at 768 locations in New Hampshire’s
White Mountains, low-elevation species have
moved predominantly upslope between 1993 and
2009 while nearly all high-elevation species have
moved downslope. The variation in inferred
altitudinal movements of birds among these
studies may be because of real geographic
variation in the degree of climate change,
geographic variation in species’ responses to
climate, or it may reflect the differences in the
survey methods employed or the spatial and
temporal scale of the analyses.
747Kirchman and Van Keuren ALTITUDINAL RANGE SHIFTS

TABLE 1. Altitudinal ranges of bird species surveyed on Whiteface Mountain, Essex Co., NY, in 1974 (upper, light
shading) and 2013–14 (lower, dark shading). Shifts, in meters (m), over the 40-year interval are reported for the upper
boundary and lower boundary of altitudinal ranges and for the abundance-weighted mean elevation, except for species that
were encountered in only one survey period (denoted with ‘na’). Species whose range boundaries in both survey periods
included the lowest or highest survey points, which precluded detecting boundary shifts, are denoted with —.
748 THE WILSON JOURNAL OF ORNITHOLOGY Vol. 129, No. 4, December 2017

The diversity of inferred altitudinal movements
of birds over the past few decades is mirrored by
the range of findings with respect to forest ecotone
movements. The magnitude and direction of the
movement that we found of lower (þ85.90 m) and
upper (þ123.06 m) altitudinal boundaries and of
abundance-weighted mean altitudes (þ82.8 m)
closely matches the movement of the ecotone
between northern hardwood forest and boreal
forest (þ91 to þ119 m) in the Green Mountains
of Vermont from 1964 to 2004 (Beckage et al.
2008). But whereas Beckage et al. (2008)
TABLE 1. Continued.
749Kirchman and Van Keuren ALTITUDINAL RANGE SHIFTS

documented uphill movement of northern hard-
wood tree species into the former boreal zone in
their forest plots, Foster and D’Amato (2015)
found that ecotones on most mountains in Vermont
and New Hampshire remained stable or moved
downslope between 1991 and 2010. It seems that
when it comes to documenting the effect of climate
change on biotic communities, studies conducted
at small spatial scales over long periods of time are
often contradicted by studies conducted at larger
spatial scales over shorter periods.
We found daily minimum temperature increased
more than daily maximum temperature over the
last 40 years in the Adirondacks, a pattern that is
consistent with trends globally (Alexander et al.
2006) and that is predicted to continue in the 21
st
century (Sillmann et al. 2013). Average minimum
temperatures are known to be an important
limitation of bird ranges (Zuckerberg et al.
2011), and may especially affect upper elevational
limits (DeLuca and King 2017). The peak in
species richness (Fig. 2) has shifted uphill at
Whiteface Mountain because the lower elevational
boundary for many species has shifted uphill,
resulting in fewer species at lower elevations and
enriched communities at higher elevations. We
also find that the average movement of the upper
boundary has outdistanced that of the lower
boundary, resulting in more bird species that have
expanded the breadth of their altitudinal ranges
than have lost ground, and in a significant change
in elevational extents when considering all species
together. Our results indicate that predictions based
on climate niche models (Lambert et al. 2005,
Rodenhouse et al. 2008, Ralston and Kirchman
2013) of birds being pushed off the tops of
mountains at the southern periphery of the boreal
forest are not yet being realized. Some studies
have used the adiabatic lapse rate of 0.58 8C per
100 m elevation to make simple predictions of
altitudinal shifts in the face of warming tempera-
tures (e.g., Chen et al. 2008). The weighted mean
altitude shift we observed (þ82.8 m) is far less than
the adiabatic lapse rate would predict based on the
warming in the Adirondacks between 1974 and
2014 (þ324 m for the 1.88 8C increase in maximum
daily temperature, þ424 m for the 2.46 8C increase
in daily minimum temperature), but we caution that
such predictions ignore the many complexities of
niche tracking, assume a simple linear response to
temperature increase, and do not account for the
many ways one could calculate temperature change
from 40 years of weather station data or calculate
the combined altitudinal range shifts of many
species.
The heterogeneity of altitudinal movement
among species has created novel bird communities
on Whiteface Mountain, especially at the highest
elevations, and it is unknown how these shifts are
affecting species interactions. Several species,
including Yellow-bellied Flycatcher, Ruby-
crowned Kinglet, Swainson’s Thrush, American
Robin, and Purple Finch, have expanded or shifted
their ranges to the highest survey station, creating
a bird community above 1,400 m that is now
roughly twice as diverse as it was 40 years ago.
Evidence from song playback experiments indi-
cates that the Swainson’s Thrush is more aggres-
FIG. 4. Abundance-weighted mean altitudes, in meters above sea-level, of 42 bird species encountered on Whiteface
Mountain, NY, in 1974 and in 2013–2015. The diagonal line indicates equal elevation in both survey periods such that points
above the line represent upslope shifts and points below the line represent downslope shift.
750 THE WILSON JOURNAL OF ORNITHOLOGY Vol. 129, No. 4, December 2017

sive than the Bicknell’s Thrush in areas where they
co-exist (Freeman and Montgomery 2016), a result
that is worrisome for the threatened Bicknell’s
Thrush in light of our finding that the altitudinal
range of Swainson’s Thrush now completely
overlaps that of Bicknell’s Thrush on Whiteface
Mountain. Ralston et al.’s (2015) analysis of point
count data for 14 species of spruce-fir forest
obligates or associates found significant population
declines over shorter time periods (up to 24 years)
in four species that were detected in our surveys,
including Bicknell’s Thrush. With respect to the
other significant decliners, we found that Yellow-
bellied Flycatcher has shifted its upper boundary,
expanding its altitudinal range breadth to include
the top of the transect, whereas Magnolia Warbler
and Blackpoll Warbler have shifted their lower but
not their upper boundaries and appear to have lost
ground. The plot of weighted mean elevations
from the two survey periods (Fig. 4) reveals two
clusters of species, above and below 800 m, which
correspond to the boreal forest avifauna and the
northern hardwoods avifauna, respectively. We
note that in each cluster there is a similar ratio of
species moving uphill versus downhill (13 up
versus 4 down for boreal birds, 13 versus 5, with 4
showing no movement for northern hardwoods
species). We interpret this to indicate that rising
temperatures are not disproportionately affecting
the altitudinal ranges of boreal forest specialists,
but rather species whose abundance is centered on
either side of the forest ecotone are equally likely
to be moving uphill.
Although we found evidence of both increasing
summer temperatures and a preponderance of
uphill movement of species ranges, we caution
that some of the changes to the Adirondack
avifauna that we have documented may not be
responses to climate warming. Our detection of the
Common Raven, a species not recorded in 1974, is
likely because of its range-wide increase in
abundance and repopulation of its historic geo-
graphic range in recent decades, especially since
the 1990s (Boarman and Heinrich 1999). The
Common Raven was nearly extirpated from
eastern North America in the early and mid-20
th
Century, and began to recover in the late 1970s
(McGowan 2008). The Common Raven certainly
occurred in the Adirondacks in 1974, but even in
this historic stronghold the species has become
much more abundant and widespread in the last
few decades, increasing by 175%between 1985
and 2005 (McGowan and Corwin 2008). A second
case is our detection at the two lowest survey
stations of six species that are common at low
elevations in New York but were not found by
Able and Noon. It is tempting to attribute this
observation to movement uphill into the lowest
portion of the transect. However, changes in land
use may be a contributing factor, as these species
(Eastern Wood-Pewee, Eastern Phoebe, Great
Crested Flycatcher, Common Yellowthroat, Chip-
ping Sparrow, and Song Sparrow) tolerate human
disturbance well and favor open habitats or forest
edges, and the forest surrounding the survey
stations at 500 m and 650 m occur below the toll
gate on the Whiteface Mountain Veterans’ Memo-
rial Highway, where the land is privately owned
and the forest is fragmented with low-density
residential and commercial development. Historic
satellite images of the transect area from Google
Earth reveal the addition of two houses and the
clear-cutting of a 250 m 3250 m forest plot along
this stretch of road sometime between 1995 and
2006. However, above the toll gate the forest has
remained undisturbed and land-use has not
changed over the 40-year period of our resurvey
study. This increases our confidence that the
altitudinal range shifts we document above 650
m elevation are not likely to be because of changes
in land use, but are responses to warming
temperatures or some other natural changes such
as forest succession or demographic expansion of
bird populations.
Our resurvey of Whiteface Mountain shows that
altitudinal range shifts of montane bird species are
observable on decade time scales at the southern
periphery of the boreal forest, and that these
changes are correlated with a regional breeding
season temperature increase over the same time
period. Resurveys of additional field sites, includ-
ing the other mountains in New York and Vermont
surveyed by Able and Noon (1976), would be
valuable in addressing the variety of responses we
found among species, as well as resolving the
discrepancies among studies of altitudinal range
shifts of birds in eastern North America. One area
of consensus among studies is the pervasive
reshuffling of bird communities that results from
the heterogeneity of altitudinal range shifting
among species. This discovery may have impor-
751Kirchman and Van Keuren ALTITUDINAL RANGE SHIFTS

tant conservation implications and demands fur-
ther study.
ACKNOWLEDGMENTS
We are indebted to Dr. Kenneth P. Able for saving his
original data sheets for 40 years and sending them to us as
we planned to replicate the surveys he conducted with Barry
Noon in 1973 and 1974. We thank Aaron Kellett from
Whiteface Lake Placid Ski Center, and Paul Casson from the
State University of New York Atmospheric Sciences
Research Center, Whiteface Mountain Field Station, for
permission to conduct this research and for access to the toll
road up Whiteface Mountain in the pre-dawn hours. Field
work was funded by the New York State Museum, Division
of Research and Collections. For helpful discussions that
improved the study we thank Ken Able, Joan Collins,
Alyssa FitzGerald, and Joel Ralston. We thank Brian Bird
for making the maps in Figure 1. We thank two anonymous
reviewers for helpful comments that improved the paper.
Author contributions: JJK conceived the idea and designed
the study. JJK and AEV collected and summarized the data.
JJK analyzed the data and wrote the paper.
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