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Emperor penguins require stable fast ice, sea ice anchored to land or ice shelves, on which to lay eggs and raise chicks. As the climate warms, changes in sea ice are expected to lead to substantial declines at many emperor penguin colonies. The most southerly colonies have been predicted to remain buffered from the direct impacts of warming for much longer. Here, we report on the unusually early breakup of fast ice at one of the two southernmost emperor penguin colonies, Cape Crozier (77.5°S), in 2018, an event that may have resulted in a substantial loss of chicks from the colony. Fast ice dynamics can be highly variable and dependent on local conditions, but earlier fast ice breakup, influenced by increasing wind speed, as well as higher surface air temperatures, is a likely outcome of climate change. What we observed at Cape Crozier in 2018 highlights the vulnerability of this species to untimely storm events and could be an early sign that even this high-latitude colony is not immune to the effects of warming. Long-term monitoring will be key to understanding this species' response to climate change and altered sea ice dynamics.
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Signicant chick loss after early fast ice breakup at a high-latitude
emperor penguin colony
ANNIE E. SCHMIDT and GRANT BALLARD
Point Blue Conservation Science, 3820 Cypress Drive, #11 Petaluma, CA 94954, USA
aschmidt@pointblue.org
Abstract: Emperor penguins require stable fast ice, sea ice anchored to land or ice shelves, on which to lay
eggs and raise chicks. Asthe climate warms, changes in sea ice are expected to lead to substantial declines
at many emperor penguin colonies. The most southerly colonies have been predicted to remain buffered
from the direct impacts of warming for much longer. Here, we report on the unusually early breakup of
fast ice at one of the two southernmost emperor penguin colonies, Cape Crozier (77.5°S), in 2018, an
event that may have resulted in a substantial loss of chicks from the colony. Fast ice dynamics can be
highly variable and dependent on local conditions, but earlier fast ice breakup, inuenced by
increasing wind speed, as well as higher surface air temperatures, is a likely outcome of climate
change. What we observed at Cape Crozier in 2018 highlights the vulnerability of this species to
untimely storm events and could be an early sign that even this high-latitude colony is not immune to
the effects of warming. Long-term monitoring will be key to understanding this speciesresponse
to climate change and altered sea ice dynamics.
Received 3 April 2019, accepted 19 November 2019
Key words: Cape Crozier, climate change, sea ice
Introduction
Emperor penguins (Aptenodytes forsteri, Gray) depend on
stable fast ice to breed successfully (with a few exceptions
of historically land-based colonies) (Wienecke 2010). As
the climate warms, sea ice thickness and extent are
expected to decrease, negatively impacting many
emperor penguin colonies, particularly those at latitudes
north of 70°S (Barbraud & Weimerskirch 2001,
Jenouvrier et al. 2009,2012,2014, Ainley et al. 2010).
Model predictions indicate that more southerly habitats
should remain suitable for much longer (Ainley et al.
2010, Jenouvrier et al. 2014).
The emperor penguin colony at Cape Crozier is the rst
known breeding location for the species, and was rst
discovered in 1902 (Scott 1905). It is one of the
southernmost emperor penguin colonies, with only one
known colony located at higher latitude (Gould Bay in
the Weddell Sea, 77.7°S) (Fretwell et al. 2012). It is one
of only a few emperor colonies that are regularly
monitored, with chick counts spanning several decades.
We have observed the emperor colony every year since
1996, with formal counts of chicks conducted annually
since 2001, complementing surveys conducted by
Kooyman and colleagues (Barber-Meyer et al.2007,
Kooyman et al. 2007, Kooyman & Ponganis 2016) and
previous counts by W. Sladen and colleagues (Ainley
et al. 1978) and others (Stonehouse 1964) beginning in
1960. Although the exact location of the colony has
varied over the years, it is always dependent on fast
ice between the Ross Ice Shelf (RIS) and Ross Island
(Kooyman et al. 1971, Kooyman 1993). Since the
beginning of this study (1996), the colony has primarily
been located in the fast ice leads that form in the rifts
in the RIS, but it occasionally has moved out of the
cracks onto the ice between land and the shelf. The
fast ice leads are typically very stable, offer shelter
from the wind and retain fast ice longer than
surrounding areas.
In 2018, the unusually early breakup of the fast ice
between Ross Island and the RIS resulted in a
substantial loss of chicks. Although previous breeding
failures have been documented at this colony, they were
attributed to unusual conditions precipitated by the
collision of a large iceberg (B15A) with the RIS that
resulted in no available leads or stable fast ice (Kooyman
et al. 2007, Kooyman & Ponganis 2016). At a time when
sea ice extent and concentration are in steep decline in
many sectors of the polar ocean (Stammerjohn et al.
2012, Scott 2019), the importance of monitoring the
status of ice-obligate species is heightened. Here, we
extend the previously published (Barber-Meyer et al.
2007, Kooyman & Ponganis 2016) time series of Cape
Antarctic Science page 1 of 6 (2020) © Antarctic Science Ltd 2020. This is an Open
Access article, distributed under the terms of the Creative Commons Attribution licence
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distribution, and reproduction in any medium, provided the original work is properly cited. doi:10.1017/S0954102020000048
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Crozier emperor penguin chicks with data through 2018
and comment on the potential for climate-related
changes to continue to affect this colony.
Methods
Emperor penguin chicks at the Cape Crozier colony
(77.455°S, 169.270°E) were counted annually in late
November to early December, coinciding with the time
of year when most adults were foraging at sea and chicks
were generally alone at the colony but had not yet begun
to leave (edge) (Kooyman et al. 2007). Beginning in
2006, chicks were counted from photographs using
either ArcMap (ESRI 2008) or open-source software
(iTag) (https://sourceforge.net/projects/itagbiology).
Photographs were taken either from the sea ice or from
a higher land-based vantage point on Ross Island and
overlaid manually in ArcMap, or stitched together using
Adobe Photoshop. Photographs in 2018 were
counted by two independent observers and the average
of the two counts was used. The average edging date of
chicks was estimated each year as the date after which
more than 50% of the chicks had left the area of the
colony. Twice-daily weather observations, including low
temperature (°C) and maximum wind gusts (km h
-1
),
were recorded at a weather station established in a
base camp 2.5 km from the emperor penguin colony.
Mean daily low temperature and average maximum
wind gusts were calculated over the rst 2 weeks in
December each year (the critical period just prior to
chick edging).
Results
The Cape Crozieremperor penguin colony was in a period
of growth when the mega-iceberg B15A collided with the
RIS early in 2001 (Kooyman et al. 2007). By March 2001,
one end of B15A had settled between the RIS and Ross
Island at Cape Crozier, breaking off the rifts where
emperor penguins typically breed (Kooyman et al.
2007). The colony went from 1201 chicks in 2000 to 0
chicks in 2001. A small number of chicks were present in
200204, but a second complete failure occurred in 2005
(Kooyman et al. 2007). After the effects of the B15A
iceberg dissipated in 2005, the Cape Crozier emperor
colony experienced another period of rapid growth,
sustained through to the present (Fig. 1). The positive
trend in chick numbers was signicant over this period
(Pearson correlation r= 0.96, P< 0.001), with the colony
adding an average of 96 chicks per year from 2006 to
2018. Annual growth rates averaged 17.7%, but were
punctuated periodically by large growth spurts every
23 years, including a 70% increase from 2006 to 2007,
a 37% increase from 2008 to 2009, a 52% increase from
2011 to 2012 and a 46% increase from 2014 to 2015
(Fig. 2). Since the last growth spurt, chick numbers have
remained high, and the 2018 count on 1 December
(n= 1911) was the highest on record. The chick counts
over the most recent 4 years were all higher than the
previous high of 1325 recorded in 1960 (Fig. 1).
On 4 December 2018, 3 days after the high count, a
majority of the fast ice between the RIS and Ross Island
broke up during a storm (sustained winds of 7593 km h
-1
and gusts of up to 119 km h
-1
recorded by the camp
Fig. 1. Emperor penguin chick counts at
Cape Crozier from 1960 through
2018. Dark grey bars are counts
previously published by Kooyman &
Ponganis (2016) and blue bars are
ground counts recorded by this study.
The light grey shaded area indicates
the years when the colony was
impacted by mega-iceberg B15A.
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weather station). Fast ice remained in the rifts in the ice
shelf, but there was open water at the mouth of the rifts
(Fig. 3). A day after the breakup, on 5 December, we
noted several large groups of emperor penguin chicks that
were on free-oating ice oes near the main colony
(Fig. 3b). The subsequent photographs and count from
6 December revealed that 1051 chicks remained on the
fast ice in the rift, but the oes, bearing 860 chicks (45%
of the chicks in the colony), were gone (Fig. 3c). The
number of adults at or near the colony increased from
321 on 1 December to 814 on 6 December, with most
adults gathered in groups with few or no chicks.
The average edging date from 1996 to 2017 was
23 December, 19 days later than the breakup in 2018.
The average overnight low temperature for the rst
2 weeks in December 2018 was -5.62°C, 0.52°C higher
than the 200217 average (-6.14°C), but this was only
the eighth warmest early December in the time series
(Fig. 4a). No trend was evident in the early December
low temperature, but there was a signicant trend
towards increasing maximum wind speed over the course
of the study (Pearson correlation r= 0.48, P= 0.049)
(Fig. 4b). The average daily maximum wind speed for
early December 2018 was 54.4 km h
-1
, the third highest
since 2002 (Fig. 4b).
Discussion
Emperor penguins rely heavily on seasonal fast ice,
making them vulnerable to climate-driven changes in
wind speed, fast ice extent and duration, as well as
Fig. 2. Annual growth rate of chick counts during post-iceberg
recovery, 200618.
Fig. 3. a. Photograph showing fast ice between the Ross Ice Shelf and Ross Island and the location of the emperor penguin colony
on 3 December 2018, the day before the fast ice broke up. b. Close-up photograph from 5 December 2018, the day after the storm,
showing groups of emperor penguin chicks on two separate ice oes that subsequently disappeared. The Ross Ice Shelf is visible
in the background. c. Photograph from 7 December 2018, 3 days after the storm, showing the extent of the fast ice breakout, and
ice oes with emperor penguin chicks missing. Photographs by A.E. Schmidt and G. Ballard.
3EMPEROR PENGUIN CHICK LOSS
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unusual storm events (Fretwell & Trathan 2019, Trathan
et al. 2019). As chicks become more independent during
the crèche stage, they begin to spread out and move
towards the ice edge, where they may become
particularly vulnerable to the storm events that lead to
early fast ice breakup. Although periodic breeding
failures or years of low breeding output at emperor
colonies are not unheard of (Kooyman & Ponganis
2016, Fretwell & Trathan 2019), these events will likely
become more frequent as the climate warms (Trathan
et al. 2019). As the sea ice season and stability decline at
lower latitudes, many emperor penguin colonies are
predicted to decrease in size or disappear (Jenouvrier
et al. 2009, Ainley et al. 2010, Trathan et al. 2011,2019).
The Ross Sea may become a refuge for this and other
ice-obligate species as populations shift south
(Jenouvrier et al. 2009,2014, Ainley et al. 2010). Indeed,
movement between colonies may be a regular and
adaptive occurrence for the species that enables it to
cope with variable fast ice over the long term (LaRue
et al. 2015, Cristofari et al. 2016).
Cape Crozier is one of the southernmost emperor
penguin colonies and also one of the smallest. It has
displayed appreciable variability in chick counts over the
decades, leading to the suggestion that the extreme
periphery of the range also constitutes marginal habitat
(Kooyman 1993, Barber-Meyer et al. 2007). The fast ice
breakup at Cape Crozier in 2018 was the earliest
observed in the past 20 years. While no similar events
were observed over several years of observations during
the 1960s1980s (Ainley et al. 1978, Ainley personal
observation, 198083), the colony at that time was much
more exposed to ocean swells (Kooyman et al. 1971),
which contribute to fast ice breakup (Kim et al. 2018).
Its small size through that period may indicate a more
frequent occurrence of low chick output, perhaps due to
unstable ice. Since then, photographs from Kooyman
et al. (1971), Kooyman (1993) and this study indicate
that the edge of the RIS and the accompanying
sheltering rifts have moved several kilometres further
north (see also Keys et al. 1998). The advancing ice edge
has led to an increase in the suitable fast ice habitat
between the RIS and Ross Island, perhaps contributing
to the recent observed growth at the Cape Crozier colony.
This recent growth may also be partly attributed to
individuals moving to Cape Crozier from the nearby
Beaufort Island colony (65 km north-west, 76.933°S,
166.833°E). Aerial surveys and satellite images suggest
that the colony at Beaufort Island has declined in recent
years, from a high of over 2000 chicks in the year 2000
(Kooyman & Ponganis 2016) to no chicks present in
2011 (Kooyman & Ponganis 2016) and 2016 (Ainley
personal observation, 2016) and only 500 adults in 2018
(LaRue unpublished data, 2018). Early fast ice breakup
at Beaufort Island in 2011 led to a catastrophic loss of
chicks from that colony (Kooyman & Ponganis 2016),
and subsequent years of poor fast ice conditions may
have encouraged penguins to move to Cape Crozier.
Although the chick loss from the early fast ice breakup
may have been severe, we do not know that all of the chicks
perished. Some of the chicks were already large and mostly
feathered when they oated away, and they may have
survived the forced early edging. Depending on how
far the oes drifted, their parents may have found them
and provided one or two more meals. However, these
chicks may have been separated from their parents
19 days ahead of the average edging date for the
colony, suggesting that many would not have been ready
to be independent. The large increase in adults present
near the colony after the breakup indicates that many
adults were still intending to feed the chicks that went
missing and waited around at the colony longer than
usual when they could not locate them.
The increasing trend in early December wind speeds
that we observed locally at Cape Crozier is consistent
with model predictions (Ainley et al. 2010) for the
Fig. 4. a. Mean 24 h low temperature and b. average daily
maximum wind gusts for the rst 2 weeks of December,
200218, measured at a local weather station located 2.5 km
from the emperor penguin colony. Trend lines represent linear
regression with 95% condence intervals.
4ANNIE E. SCHMIDT & GRANT BALLARD
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region and may have been a contributing factor in the early
breakup that year: higher wind speeds have been
associated with the earlier breakup of fast ice in nearby
McMurdo Sound, as well as other locations (Heil 2006,
Massom et al. 2009,Kimet al. 2018).
The early fast ice breakup at Cape Crozier in 2018
coincided with a year of anomalously quick retreat of
sea ice in the Ross Sea and Antarctica as a whole.
Continent-wide, sea ice extent declined at a rate of
253 000 km
2
per day through December, the highest rate
of loss in the satellite record (Scott 2019). Lower
concentrations of pack ice may also contribute to earlier
fast ice breakup by allowing more ocean swell to directly
impact fast ice edges (Massom et al. 2018). Although
the early breakup at Cape Crozier may just be an
anomaly, it is concerning as it could indicate that the
impacts of rising global temperatures have already
reached the southern limit of the emperor penguins
range. This year offered a glimpse of a scenario that is
likely to occur more often, and at more colonies, as
global temperatures continue to rise.
Acknowledgements
We thank the many biologists who have participated in the
chick counts, especially Viola Toniolo for her 5 year
contribution and David Ainley, who also provided many
useful comments on an earlier draft. We are grateful to
Michelle LaRue and Gerry Kooyman who provided
additional reviews. We also thank the US Antarctic
Program for providing excellent logistical support every
year. This is Point Blue Contribution 2264.
Author contributions
GB designed the study, AES analysed the data and both
authors collected the data and wrote the paper.
Financial support
Funding for eldwork and for preparing this manuscript
was provided by the National Science Foundation Ofce
of Polar Programs grants 0125608, 0439759, 0944141,
1543541 and 1543498.
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Defining reliable demographic models is essential to understand the threats of ongoing environmental change. Yet, in the most remote and threatened areas, models are often based on the survey of a single population, assuming stationarity and independence in population responses. This is the case for the Emperor penguin Aptenodytes forsteri, a flagship Antarctic species that may be at high risk continent-wide before 2100. Here, using genome-wide data from the whole Antarctic continent, we reveal that this top-predator is organized as one single global population with a shared demography since the late Quaternary. We refute the view of the local population as a relevant demographic unit, and highlight that (i) robust extinction risk estimations are only possible by including dispersal rates and (ii) colony-scaled population size is rather indicative of local stochastic events, whereas the species’ response to global environmental change is likely to follow a shared evolutionary trajectory.
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Sea ice conditions in the Antarctic affect the life cycle of the emperor penguin (Aptenodytes forsteri). We present a population projection for the emperor penguin population of Terre Adélie, Antarctica, by linking demographic models (stage-structured, seasonal, nonlinear, two-sex matrix population models) to sea ice forecasts from an ensemble of IPCC climate models. Based on maximum likelihood capture-mark-recapture analysis, we find that seasonal sea ice concentration anomalies (SICa ) affect adult survival and breeding success. Demographic models show that both deterministic and stochastic population growth rates are maximized at intermediate values of annual SICa , because neither the complete absence of sea ice, nor heavy and persistent sea ice, would provide satisfactory conditions for the emperor penguin. We show that under some conditions the stochastic growth rate is positively affected by the variance in SICa . We identify an ensemble of five general circulation climate models whose output closely matches the historical record of sea ice concentration in Terre Adélie. The output of this ensemble is used to produce stochastic forecasts of SICa , which in turn drive the population model. Uncertainty is included by incorporating multiple climate models and by a parametric bootstrap procedure that includes parameter uncertainty due to both model selection and estimation error. The median of these simulations predicts a decline of the Terre Adélie emperor penguin population of 81% by the year 2100. We find a 43% chance of an even greater decline, of 90% or more. The uncertainty in population projections reflects large differences among climate models in their forecasts of future sea ice conditions. One such model predicts population increases over much of the century, but overall, the ensemble of models predicts that population declines are far more likely than population increases. We conclude that climate change is a significant risk for the emperor penguin. Our analytical approach, in which demographic models are linked to IPCC climate models, is powerful and generally applicable to other species and systems.