Climate-related range shifts in Arctic-breeding
shorebirds
RUNNING HEAD
Range shifts in Arctic-breeding shorebirds
ABSTRACT
Aim: To test whether the occupancy of shorebirds has changed in
the eastern Canadian Arctic, and whether these changes could indicate
that shorebird distributions are shifting in response to long-term
climate change
Location: Foxe Basin and Rasmussen Lowlands, Nunavut, Canada
Methods: We used a unique set of observations, made 25 years
apart, using general linear models to test if there was a relationship
between changes in shorebird species’ occupancy and their Species
Temperature Index, a simple version of a species climate envelope.
Results: Changes in occupancy and density varied widely across
species, with some increasing and some decreasing. This is despite that
overall population trends are known to be negative for all of these
species, based on surveys during migration. The changes in occupancy
that we observed were positively related to the Species Temperature
Index, such that the warmer-breeding species appear to be moving into
these regions, while colder-breeding species appear to be shifting out
of the regions, likely northwards.
Main Conclusions: Our results suggest that we should be
concerned about declining breeding habitat availability for bird species
whose current breeding ranges are centred on higher and colder
latitudes.
KEYWORDS
Avian, Climate tracking, Conservation, Ecology, Global change, Polar,
Poleward shifts, Range dynamics, Re-distribution, Wader
INTRODUCTION
Over the past century, many species have shifted their distributions in
response anthropogenic influences. One increasingly important driver of
distributional shifts is climate change, with species moving towards
higher latitudes and higher elevations in response to a warming climate
(Parmesan and Yohe 2003; Chen et al. 2011). For example, the northern
limit of birds’ ranges measured by the North American Breeding Bird
Survey shifted northward at a rate of 2.35 km/yr between 1967 and 2002
(Hitch and Leberg 2007). Likewise, butterfly and moth ranges have
expanded northward in Finland (Mikkola 1997), Great Britain (Hill et al.
2002) and across Europe (Parmesan et al. 1999). These changes in
species’ range limits are an important measure of how species are
redistributing in response to climate change. Patterns of species
density and community composition are shifting as well, creating novel
ecological communities (Devictor et al. 2012; Kampichler et al. 2012;
Lurgi, López, and Montoya 2012). Estimating the distribution of species
has become a very active field of research, responding to concerns about
how accelerating global environmental change will reshape the world’s
ecosystems (Guisan and Thuiller 2005).
Identifying shifts in distribution in response to climate change
requires long-term and large-scale species data, but the regions where
the climate is changing fastest are often those where such data are
sparse, making it impossible to directly measure shifts in species
distribution (Shirey et al. 2021; Daskalova et al. submitted). The
Arctic is a case in point. Here, temperatures are rising three times
faster than the global average (AMAP 2021). Yet, even for birds, a taxon
comparatively well monitored globally, the Arctic lacks consistent
monitoring that would allow for rigorous analyses of climate effects on
bird abundances and distributions (Smith et al. 2020; Aronsson et al.
2021). Research in remote Arctic locations is logistically complicated
and expensive, costing on average eight times more than similar studies
at a southern location (Mallory et al. 2018). More populated areas can
support citizen science programs such as eBird (Johnston et al. 2021)
and large-scale surveys such as the Christmas Bird Count or various
regional and national Breeding Bird Survey programs offer immense
quantities of distributional data that can be used to directly measure
distribution shifts (Curley, Manne, and Veit 2020; Devictor et al. 2008;
Lindström et al. 2013). However, in the Arctic, no regularly repeated,
range-wide surveys upon which to base assessments of distributional
change in the Arctic have yet been completed.
Despite the challenges, information about species distributions in the
Arctic will be increasingly important for supporting conservation
policies and protected areas being developed to protect northern species
from increasing human presence and a rapidly warming climate. Melting
ice is likely to lead to increases in shipping and resource extraction
(Arbo et al. 2013). Arctic species are also particularly vulnerable to
climate change due to three unique geographic factors that are leading
to an “Arctic squeeze” which has the potential to dramatically limit
the capacity of Arctic species to adaptively shift their ranges (Vincent
2020; Meltofte et al. 2007). First, the surface area of the Earth
decreases as latitude increases towards a fixed end point at the pole,
limiting options for northern expansion of habitats (Gilg et al. 2012).
Second, northern expansion of terrestrial habitats cannot occur in
regions that are bordered to the north by the Arctic Ocean; in many
locations there is no more northerly landmass available for terrestrial
species to expand into (Wauchope et al. 2017). Third, the southern
border of tundra habitat is moving northwards, as shrubs and trees also
shift northwards in response to climate change, encroaching into the
open habitats preferred by many tundra-breeding species (Martin et al.
2017; García Criado et al. 2020).
In this paper, we assess if the regional population trends could
indicate whether the distributions of breeding birds are shifting in the
Canadian Arctic. We focus here on shorebirds, the most abundant and
diverse group of birds in many tundra habitats. These species are likely
to be particularly sensitive to climate change because of their highly
migratory life history, as Arctic-breeding shorebirds undertake long,
energetically expensive migrations, only have a short window available
for breeding in the Arctic, and depend on ecological synchronicities
with their invertebrate prey (Galbraith et al. 2014). Surveys providing
an index of shorebird abundance during their migrations through southern
Canada and the United States suggest that shorebird populations have
experienced pronounced declines in the past 50 years, including all of
the species studied here (Bart et al. 2012, Smith et al. 2020, Smith et
al. submitted). These declines are often attributed to habitat loss and
degradation at migratory stopovers and non-breeding sites (Thomas,
Lanctot, and Szekely 2006), but given that climate change in the Arctic
is expected to be rapid and severe, there is concern that environmental
changes to shorebird breeding habitats may increasingly cause additional
stress in these declining populations (Galbraith et al. 2014). Several
previous studies have improved our understanding of the current
distribution of Arctic-breeding birds. However, there have been no
analyses of long-term, broad-scale monitoring data to address questions
about potential changes in distribution on the Arctic breeding grounds,
as a consequence of climate change.
We used a unique set of observations, made 25 years apart across 50,000
km² of mid-Arctic tundra habitats, to test whether the occupancy of
shorebirds has changed over time, and whether these changes could
indicate that distributions are shifting in response to long-term
climate change. These data were collected as part of the Arctic Program
for Regional and International Shorebird Monitoring (PRISM), an
unprecedented Arctic-wide survey that will eventually track changes in
the population size, trends and distribution of shorebirds (Bart and
Johnston 2012). The observed summer temperature in northern Canada has
increased by 1.6°C between 1948 and 2016 (Zhang et al. 2019). We
therefore predicted that at mid-Arctic latitudes, species associated
with warmer Low Arctic breeding habitats should be moving into the regio
and observed more frequently, and species associated with colder High
Arctic habitats should be moving out of the region and observed less
frequently (Jiguet et al. 2010) (Figure 1). To test this prediction, we
represented species temperature associations using the Species
Temperature Index (STI), a simple version of a species climate envelope.
Given that the population trends for these species are negative, we were
interested to look at overall trends in survey counts in these regions
to give context to any potential distribution shifts.
The STI is the long-term average temperature experienced by individuals
of a species across their breeding range (Devictor et al. 2008). While
species distributions are much more complex than simple climate
relationships, this index has been a useful approach for describing how
population trends and demography of bird populations are responding to
climate change (P. Gaüzère et al. 2020; Princé and Zuckerberg 2015;
Godet, Jaffré, and Devictor 2011). The collective contributions of
individual species responses can give an indication of how the
ecological community is responding to change (Curley et al. 2022; Pierre
Gaüzère et al. 2019). Species with low STI consistently show more
negative population trends in response to high temperatures
(Pearce-Higgins et al. 2015). We thus predicted a positive relationship
between STI and the temporal change in shorebird occupancy, with
occupancy increasing for warmer-breeding species and occupancy
decreasing for colder-breeding species over 25 years. Given that the
large-scale population trends for these species are negative (Bart et
al. 2012, Smith et al. 2020, Smith et al. submitted), for any species
that have positive regional trends, this can be interpreted as
reflecting distributional change, rather than change in population-level
abundance.
METHODS