Results – climatic variables Temperature:

1. Impact of climate warming on whooper swan wintering phenology in Ireland R. L. Stirnemann1, Alison Donnelly 1 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 • Temperature: • 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. • 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. • NAO: • May NAO significantly influenced the peak arrival date Wind: • Wind speed and direction at the wintering ground were not found to be a significant predictor of migration parameters Figure 1. Schematic view of migration route of whooper swans wintering in Ireland and breeding in Iceland 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). 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. 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). 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. 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). Discussion 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. 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. 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). • Methods: • Daily whooper swan counts were taken from 1971- 2009 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. Conclusion: 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. References: Van der Graaf, S.A.J., Stahl, J., Klimkowska, A., Bakker, J. P. & Drent. R. H. 2006. Surfing in a green wave-how 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 Figure 4. Changes in migratory parameters over the study period with fitted linear regressions.