. The Canadian field-naturalist. Natural history. 112 The Canadian Field-Naturalist Vol. 117 arrival -?—avAprT - - - tern pi trend arrival trend 31-Mar. Year Figure 3. Trends of the dates of first observed arrival of Tree Swallows at Ellis Bird Farm near Lacombe, Alberta, and average April temperatures. of the trend line for the FOA dates was approximate- ly days/yr. Over the 44 years that TRES dates of arrivals have been recorded, the slope of the trend line for the average April temperature was approxi- mately and the slope of the trend line for the FOA dates was approximat
. The Canadian field-naturalist. Natural history. 112 The Canadian Field-Naturalist Vol. 117 arrival -?—avAprT - - - tern pi trend arrival trend 31-Mar. Year Figure 3. Trends of the dates of first observed arrival of Tree Swallows at Ellis Bird Farm near Lacombe, Alberta, and average April temperatures. of the trend line for the FOA dates was approximate- ly days/yr. Over the 44 years that TRES dates of arrivals have been recorded, the slope of the trend line for the average April temperature was approxi- mately and the slope of the trend line for the FOA dates was approximately days/yr. A conservative interpretation of the FOA and tem- perature data is that the temperature trend reflects a larger geographic trend of increasing average month- ly temperatures, and that the earlier returns appear to reflect a behavioural response to this larger geo- graphic phenomenon. Arrival dates of MOBL and TRES on their breed- ing territory are influenced by many factors, includ- ing weather on their wintering grounds and along their migration routes. For this reason, local meteo- rological conditions might not always be the most significant factor influencing FOA dates. However, given the consistency in trends of average March temperatures, average April temperatures, and in the FOA trends of both species, this correlation warrants further examination. Acknowledgments We thank Winnie Ellis and Ellis Bird Farm Ltd. for supplying FOA records and also acknowledge the Meteorological Service of Canada for providing the climate data, Brenda Dale of the Canadian Wildlife Service, Environment Canada and Bob Kochtubajda of the Meteorological Service, Environment Canada for technical reviews. This research project was sponsored in part by the Red Deer River Naturalists Society through funding sup- port from the Red Deer and District Community Foundation. Literature cited Dunn, P. O., and D. W. Winkler. 1999. Climate change has affected breeding date of tree swallo
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