Impact of climate warming on whooper swan wintering phenology in Ireland
R. L. Stirnemann
1,
1
Alison Donnelly and John O'Halloran
2
1
Centre for the Environment, Trinity College Dublin, Dublin 2, Ireland; email: stirnemr@tcd.ie
2 Department of Zoology, Ecology and Plant Science, University College Cork, Distillery Fields, North Mall, Cork, Ireland
Results – climatic variables
Figure 1. Schematic view of migration route of
whooper swans wintering in Ireland and breeding in
Iceland
Temperature:
1985
Introduction:
Change in the timing of life cycle events (phenology) of
birds has been linked to climate warming at the breeding
grounds, wintering grounds and/or en-route. Alterations
in migrational phenology have also been correlated with
large scale climatic indices (e.g. North Atlantic
Oscillation), shifts in the frequency of wind speed and
direction (Sparks & Mason 2004, Vähätalo et al. 2004)
and changes in food resources (e.g. grasses).
Figure 3. The peak departure and arrival dates were obtained
by fitting two Gaussian curves to annual data and calculating
the inflection points (indicated by arrows), Daily swan count
(indicated by points).
Though a number of studies show evidence for the
influence of increasing temperature on spring migration
of birds, few studies have considered changes in the
wintering phenology. Research however, indicates
wintering phenology has direct affects on spring arrival
dates and breeding phenology.
 Daily whooper swan counts were taken from 19712009 in Kilcolman Wildfowl Reserve, County Cork,
Ireland (Fig. 1). This dataset was used to determine
first arrival, last departure and the peak departure and
arrival dates. Peak arrival and departure dates, when
the majority of swans arrived and departed, were
determined by fitting a curve to determine the inflection
point dates (Fig.3).
 The relative influence of average monthly local
temperature (from the nearest climate station to the
wintering site), monthly NAO, wind speed and direction
(proportion of days with SW-SE and NE-NW) from the
wintering sites during migrational periods and changes
in the phenology of grass growth (covering 1982-2009)
were analysed against the arrival and departure
parameters.
NAO:
 May NAO significantly influenced the peak arrival date
 Wind speed and direction at the wintering ground were not
found to be a significant predictor of migration parameters
Discussion
Figure 2. Whooper swan (Cygnus cygnus)
commons.wikimedia.org/wiki/File:Whooper_Swan
Results - migrational parameters
 First arrival and departure peak dates
have advanced significantly at a rate of
approximately 5 days per decade (Fig.
4).
 The peak arrival date has also
increased but not significantly.
 Last departure date did not change,
resulting in a longer departure period.
 Total duration of stay has not altered in
comparison to the departure peak.
 Arrival date was found to be a good
predictor of when birds departed.
 The peak departure date significantly
effected the first arrival date of the
following year (Fig. 4).
240
220
Climate driven changes in the peak departure phenology of
whooper swans appear to be mediated through a trophic
cascade driven by increasing February temperatures. This
temperature increase has altered the phenology of early plant
growth. Primary plant growth is particularly nutrient rich and
important for the fat uptake in Arctic water fowl which is required
for fuelling migration and breeding (van der Graaf et al. 2006).
Early plant growth enables whooper swans to fulfil energetic
constraints earlier enabling the departure phenology to alter.
This change in departure could have a carryover effect
influencing the following year’s arrival date, resulting in earlier
migration in subsequent years.
200
Day (1st October=1)
Methods:
 Peak departure date is significantly correlated with the
average maximum temperatures in the first week of February.
With warmer temperatures a significant trend towards earlier
peak departure over the study period is observed. In
conjunction, in February the timing of early spring grass
growth has also increased.
Wind:
Aim:
This study aims to determine (a) if the wintering
migrational phenology of whooper swans (Cygnus
cygnus) (Fig. 1 & 2) has altered in Ireland and (b) if
observed changes in phenology are attributable to (i)
increases in temperature at the wintering site in Ireland,
(ii) changes in the North Atlantic Oscillation (NAO), (iii)
changes in wind speed and wind direction (iv) the timing
of grass growth at the wintering site.
 Local average air temperatures over 1971-2009 have
significantly increased during March, April and May in
Fermoy near the study site. The maximum temperature of the
first week of February has also significantly increased.
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160
140
120
Conclusion:
100
80
60
Climate driven changes in temperature can alter the phenology
of a primary consumer well in advance of migration through
trophic cascades by influencing energetic constraints.
40
20
0
1970
1975
1980
1985
1990
1995
2000
2005
Year of arrival at wintering grounds
First arrival
Maximum arrival point
Maximum departure point
Last departure
Figure 4. Changes in migratory parameters over the study
period with fitted linear regressions.
References:
Van der Graaf, S.A.J., Stahl, J., Klimkowska, A., Bakker, J. P. & Drent. R. H. 2006. Surfing in a green wavehow plant growth drives spring migration in the Barnacle Goose Branta leucopsis. ARDEA. 94(3):567-577
Sparks, T. H., & C. F. Mason. 2004. Can we detect change in the phenology of winter migrant birds in the UK?.
Ibis 146:57-60.
Vähätalo A. V., Rainio K., Lehikoinen A. & E. Lehikoinen. 2004. Spring arrival of birds depends on the North
Atlantic Oscillation. Journal of avian Biology. 35: 210-216