Download Climate change leads to range shift of Willy Wagtails to previously

Cygnus (2012) 1:244-252
DOI 19627551, 20656107, 21152642
RESEARCH ARTICLE__________________________________
Climate change leads to range shift of Willy Wagtails to
previously uncolonised Tasmania
Michelle Fraser• Raynuka Narayanan • Margaret Tu
Received: 22 May 2012 / Accepted: 30 May 2012
Abstract There is growing evidence climate change has affected the breeding cycles and
distribution of species worldwide and the effects of these changes are still largely unknown
for species within Australia. To explore such effects on Australian avifauna, we examined a
recent, citizen-science based dataset of sightings of Willy Wagtails (Rhipidura leucophrys)
across Australia. Our analysis was primarily confined to the comparison of current and
historical data on sightings of breeding and nesting R. leucophrys and researching the impact
of global warming on Australia’s climate. The distribution of R. leucophrys was seen to have
shifted south to Tasmania and South-East Australia, whilst breeding season remained
unchanged. This range shift was attributed to rising temperatures and variable rainfall across
mainland Australia resulting in Tasmania and coastal South-East Australia becoming suitable
habitats for R. leucophrys due to their milder temperatures and steady rainfall. We conclude
that R. leucophrys will extend their range to more temperate climates rather than change the
timing of their breeding season as a result of rising temperatures.
Keywords – Rhipidura leucophrys, climate change, distribution, range shifts, Australian
birds, Tasmania
1 Introduction
Global warming has altered physical and biological systems and there is growing evidence it
has affected the distribution and timing of biological events for many plant and animal
species (Cotton, 2003). However, the implications of global warming for avifauna in
particular are of growing concern, as evidence for ecological effects in birds is rising
(Walther et al. 2002). These implications include the possible onset of earlier breeding
seasons and potential changes in geographic range, movement patterns, abundance,
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phenology, physiology, morphology and community composition (Chambers et al. 2005).
Most studies on the effects of climatic warming have been conducted on birds in the Northern
Hemisphere, which differs greatly ecologically and climatically from the Southern. As a
result of this, knowledge of how climate change has affected Australian avifauna has been
relatively poor until recently. As knowledge of the systems in both hemispheres is crucial in
understanding the full effects of climate change, we focus on the effects of climate change on
Australian birds with particular reference to Willy Wagtails (Rhipidura leucophrys)
(Chambers et al. 2005).
The impact of climate change on a species will be determined by its adaptive ability. Average
continental temperatures in Australia have risen by 0.9 °C since 1900, with most of this rise
occurring after 1950. Temperatures are projected to rise a further 1 degree over the next two
decades (Birds Australia 2007, Hughes, 2003). Recent studies indicate Australian birds have
evolved to cope with high levels of year-to-year variability in climate and are thus able to
adjust life-events accordingly. Observed changes in phenology have not been as drastic as for
some species from the Northern Hemisphere where increases in breeding dates of 2-5 days
per decade since the 1970s have been recorded. However, range expansions, with increasing
species distribution southward as much as 200-300 kilometres over the past two decades have
been noted for Australian birds (Chambers et al. 2005, Hughes, 2003). This evidence
indicates the ability for a species to adapt by moving with its changing climatic zone. Global
warming is predicted to move climatic zones poleward and for Australia this implies climatic
zones moving to the south. From this evidence, changes in geographic regions of mobile
species such as birds can be expected. It can therefore be inferred that ‘adaptable species that
have broad climatic ranges and a strong ability to disperse will most likely be advantaged’,
while ‘species with narrow climatic ranges, small populations and specific habitat
requirements will most likely be disadvantaged’, facing declining numbers and the possibility
of extinction (Birds Australia 2007).
In this study, we explored the effects of climate change on the Willie Wagtail by reviewing a
recent dataset of observations obtained from ClimateWatch of this species. We compared
these observations to known changes in the Australian climate. R. leucophrys are highly
adaptive, insectivorous, passerine birds, native to Australia and have responded well to
human alteration of the landscape. Historically, these birds have been listed as either absent
or as vagrants to Tasmania due to its cooler climate, preferring warmer temperatures for its
breeding conditions (Birds in Backyards: Willie Wagtail, ClimateWatch: Willie Wagtail).
However, recent studies indicate Tasmanian temperatures have risen at an average rate of 0.1
°C per decade since the 1950s and are projected, at most, to rise on average 2.6 to 3.3 °C over
the entire 21st century (Grose et al. 2012). These changes in temperature have coincided with
increased sightings of R. leucophrys in Tasmania. In this paper we report new data that
suggests R. leucophrys have formed new breeding colonies in Tasmania, extending their
distribution south due to global warming and this indicates strong adaptive ability in response
to climate change. We hypothesised that R. leucophrys will extend their range to more
temperate climates rather than change the timing of their breeding season as a result of
elevated temperatures.
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2 Materials and Methods
The first aspect of our research was to determine the changes in the distribution of breeding
and mating R. leucophrys over time. To do so, we examined a recent dataset of 945 sightings
of R. leucophrys nationwide from the online citizen science program, ClimateWatch.
ClimateWatch was established in 2009 to study the phenological changes in commonly found
species, used as ‘indicator species’, to record the possible effects of climatic warming.
Our paper’s focus is on nesting habits of R. leucophrys and so the sightings we used from the
ClimateWatch dataset were those relating only to breeding, namely those of: 'bird on nest',
'bird on eggs', ‘bird on chicks’, ‘courting’, ‘mating’ and 'bird feeding young'. This data was
manipulated using Microsoft Excel to exclude irrelevant data and generate a spreadsheet of
data relevant to our area of research. After the relevant data was isolated, it was imported on
to The Living Atlas of Australia map. We used the “outline map option” of Australia from
this Atlas to show locations in Australia that R. leucophrys have recently been breeding. We
then compared this to historical data by importing onto the map outline, The Atlas of Living
Australia’s historical data on R. leucophrys which dated back to 1803. Following this, we
used the “species availability function” to find the distribution density of the Wagtails. The
map produced from both sets of data through The Living Atlas of Australia gave us an outline
in the change in breeding locations for R. leucophrys over time, allowing recent data to be
compared with historical data on the same map.
As the ClimateWatch dataset was only based on recent observations (2 years’ worth), this
data alone was not sufficient to fully determine changes in Willie Wagtail breeding
distribution. Due to this reason, we isolated data based on sightings of R. leucophrys in
Tasmania from The Living Atlas of Australia across the past century. We then used this data
to generate a graph using Microsoft Excel, plotting the number of sightings against year from
the period 1913-2012.
We also obtained climate data from the Australian Bureau of Meteorology to determine if any
temperature or rainfall changes had taken place over continental Australia or Tasmania
during the past century and examined the extent of these changes (BOM, 2012). On gathering
this data, we investigated whether the level of rainfall affects the distribution of breeding and
nesting Wagtails by mapping the isolated ClimateWatch data against the “precipitation layer”
function from The Atlas of Living Australia.
3 Results
When climate data were examined, we found that global warming has altered the Australian
climate. There was a clear warming trend in mean annual temperatures in mainland Australia
and Tasmania (Figure 1). In the period 1970-2010 mean annual temperature anomalies above
the mean were more common, while before the 1970s, it was temperature anomalies below
the mean that were more apparent. Climate data obtained also shows the effects of global
warming on particular regions of Australia. Comparatively warmer temperatures are found in
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South-Eastern areas of Australia and Tasmania as the distribution of warmer days than
average is greater in those regions when compared to the rest of Australia (Figure 2). Rainfall
throughout mainland Australia has become highly variable from year-to-year (Figure 3).
Despite this variability, rainfall has remained steady in areas such as South-East Australia and
Tasmania which have continued to experience high levels of rainfall above 600mm per
annum (Figure 4).
A
B
Fig. 1 (a) Anomalies in annual mean temperature from 1910-2010 departing from the 19611990 mean temperature of 10.4 °C in Tasmania. (b) Anomalies in annual mean
temperature from 1910-2012 departing from thr 1960-1990 mean temperature of 10.4
°C in Australia (BOM, 2012).
Fig 2. The the average annual number of heating days across Australia, over the period 1961
to 1990, calculated from a base temperature of 12 °C (BOM, 2012).
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Fig 3. Annual rainfall (mm) from 1900 to 2010 (BOM, 2012).
A
B
Fig 4. (a) The average annual rainfall across 30 years from the period 1911-1940. (b) the
average annual rainfall across 30 years from the period 1976-2005 for Australia. Note
(a) and (b) show heavy rainfall, above 900mm in the majority of Tasmania and southeastern regions of Australia. The regions also correspond to areas of increased heating
days in the heating degree days map. (BOM, 2012)
We found that changes have occurred in the distribution of R. leucophrys. This change in
distribution of can be seen in the Atlas of Living Australia map as shown in Figure 5. Current
distribution (green) has shifted south and is mainly restricted to coastal southern temperate
areas and subtropical southern regions of Australia. Willie Wagtail current distribution also
corresponded to areas that received at least 600 millimetres of rainfall (Figure 7). A sharp
increase in sightings of R. leucophrys in Tasmania from 2007 onwards was also observed
(Figure 6).
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Fig 5. The distribution of R. leucophrys in Australia. Yellow areas represent historical
sightings sourced from The Atlas of Living Australia. The green areas represent the
current distribution of R. leucophrys over the past two years based on recent sightings
recorded in the ClimateWatch dataset (ClimateWatch, 2012, The Atlas of Living
Australia, 2012).
6
Number of sightings
5
4
3
Series1
2
1
0
1900
1920
1940
1960
1980
2000
Year
Fig 6. The number of R. leucophrys sightings in Tasmania for the period 1913-2012 from
Atlas of Living Australia records (The Atlas of Living Australia, 2012).
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Fig 7. The annual distribution of rainfall from 2008-10 and the ClimateWatch data (blue
points) on breeding and nesting distribution of R. leucophrys in Australia
(ClimateWatch, 2012, The Atlas of Living Australia, 2012).
4 Discussion
Although citizen science is often questioned for its reliability, other studies have
demonstrated that it is an accurate source of previously unknown information on a species
(Mayer, 2010) and as a result, we are confident that our analysis shows R. leucophrys has
colonised Tasmania due to climate change. However, while we believe that our study offers
valuable insight into climate change related pressures on species and their responses, we feel
that the reliability of citizen science must still be addressed. Increased awareness of the
effects of climate change on Australian species may have led to greater numbers of
participants in such programs and therefore increased observations of R. leucophrys in these
regions. Observations collected by “citizen scientists” may be mistaken sightings of the
species due to the relative lack of knowledge on differentiating characteristics between
similar species. Population increase in Tasmania may have also played a role in these
increased sightings of R. leucophrys as a greater population would undoubtedly lead to more
sightings. Due to these reasons, we believe more research on the effects of climate change on
species is needed to confirm and expand these findings, particularly for Australian species.
Our study shows that recent sightings of R. leucophrys in Tasmania have risen sharply and
this indicates the birds have formed new colonies south of their known species distribution.
This reflects a range shift poleward towards cooler, wetter areas, and more temperate
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climates. As additional research has concluded that R. leucophrys were absent from Tasmania
due to the climate being too temperate for the survival of their young (Sharland, 1950), the
colonisation of Tasmania by Wagtails shows that climatic warming has resulted in Tasmania
becoming a suitable habitat for the species.
The colonisation of Tasmania by R. leucophrys may also be driven by Tasmania’s higher and
more stable rainfall levels. R. leucophrys prefer to live and breed near water (Dyrcz, 1994)
and this is supported by our data where current distribution correlates with high rainfall
regions. When data from the Atlas of Living Australia is examined with this trend in mind,
historical sightings of R. leucophrys in Tasmania coincide with either increased temperature
or decreased rainfall on the Australian mainland. This shows that when the Australian
mainland becomes unsuitable for R. leucophrys as a breeding site, they migrate to Tasmania
for this purpose. As R. leucophrys are also insectivorous, this may contribute to their
preference for high rainfall areas. Moisture has been shown to be an important factor in the
ecology of insects and higher rainfall levels may lead to the greater abundance of prey for the
Wagtails (Tauber et al. 1998). Their diet has been found to be highly adaptable, with the
proportion of each taxon in their diet varying greatly across different locations. This suggests
they feed opportunistically rather than preferentially and may have enabled them to settle
relatively easily in Tasmania (Adriano and Calver 1995). As a greater abundance of resources
is advantageous for the survival of species and their offspring (Walther et al. 2002), these
reasons may partly account for their range shift south to Tasmania for breeding and nesting.
Our findings also suggest that high adaptive ability may present opportunities for species to
gain from climate change. The range shift to Tasmania by R. leucophrys shows high adaptive
ability and has allowed the formation of a new habitat. The formation of new habitats through
range shifts have also been noted for other species in response to climate change. It has been
predicted that a change in the average annual temperature of 1 degree will correspond with a
shift in climatic zone of 100-130 kilometres in temperate areas. This is consistent with the
movement of other Australian, warmer climatic zone birds such as the Roseate Tern (Sterna
bergii) and Red-tailed Tropicbird (Phaethon rubricauda), which formed new breeding
locations south of their historical ranges in the 1950s and 60s. Furthermore, the rate of
growth and establishment of new colonies south of their historical locations appear to have
risen since the early 1980s. These changes reflect the pace of global warming and climate
change. Higher temperatures and variable rainfall distribution have caused these birds to
migrate south in favour of more temperate climates for higher chances of survival of their
offspring and this may allow them to gain from climate change (Birds Australia 2007,
Chambers et al. 2005, Hughes, 2003).
While R. leucophrys have shown high adaptive ability in their colonisation of Tasmania,
climate change is occurring at unprecedented rates and may outweigh species’ adaptation
ability (Birds Australia 2007). Tasmania remains a suitable habitat for the meantime but it is
predicted that future climate change will continue to raise Tasmania’s temperatures and shift
rainfall patterns significantly (Grose et al. 2012). The data analysed showed the birds will
travel to Tasmania when mainland conditions are unfavourable. The colonisation of
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Tasmania therefore demonstrates that the species is not able to return to its previous habitat
(continental Australia) and indicates that unfavourable conditions such as warmer
temperatures and decreased rainfall are not coming to a close in mainland Australia. Once the
colonisation of Tasmania by R. leucophrys is complete and climate change continues to raise
temperatures and disrupt rainfall patterns there, the question to ask is what will happen to R.
leucophrys when their “last resort habitat” is no longer suitable?
Acknowledgements The authors thank sub-editor Sophie Arnall and acknowledge that data sourced in this
paper is from ClimateWatch, The Atlas of Living Australia, and the Australian Bureau of Meteorology.
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