. The Canadian field-naturalist. Natural history. 2003 Lane and Pearman: Spring Return dates 111. r = 20-Apr 10-Apr 31-Mar 21-Mar 11-Mar 01-Mar 19-Feb CM °P (D CM CN degC Figure 2. Regression analysis result for first observed arrival of Mountain Bluebirds at Ellis Bird Farm near Lacombe, Alberta, versus average March temperatures. area were kept by Winnie Ellis of Lacombe, from 1958 (TRES) and 1961 (MOBL) until 1981. After 1981, FOA dates were recorded for both species by a biologist hired by Ellis Bird Farm Ltd., the non-prof- it company charged with the responsibility of carry- ing on
. The Canadian field-naturalist. Natural history. 2003 Lane and Pearman: Spring Return dates 111. r = 20-Apr 10-Apr 31-Mar 21-Mar 11-Mar 01-Mar 19-Feb CM °P (D CM CN degC Figure 2. Regression analysis result for first observed arrival of Mountain Bluebirds at Ellis Bird Farm near Lacombe, Alberta, versus average March temperatures. area were kept by Winnie Ellis of Lacombe, from 1958 (TRES) and 1961 (MOBL) until 1981. After 1981, FOA dates were recorded for both species by a biologist hired by Ellis Bird Farm Ltd., the non-prof- it company charged with the responsibility of carry- ing on the bluebird conservation efforts of Winnie and her brother, Charlie Ellis. Although FOA dates are not necessarily a true record of first spring arrival times, they do represent the last possible date that the birds returned, even if the observed arrivals did not remain in the area. There is no evidence that either species over-winters in this area. Furthermore, Charlie and Winnie Ellis and the employed biolo- gists actively searched for MOBL each spring, as did many of the Ellis' neighbours. Temperature data have been collected since 1907 at a federal agricultural research facility now known as the Agriculture and Agri-food Canada Lacombe Research Centre, located approximately 8 km north- west of the Ellis farm. The bird return observations are from an area of approximately 250 km2 sur- rounding the Ellis farm, known as the Ellis Bird Farm Management Area (so named because it is the area in which Ellis Bird Farm Ltd. continues to oper- ate a bluebird trail). Trends for MOBL FOA data and average March daily temperatures for the period of record are illus- trated in Figure 1. The trends show increasing aver- age monthly temperature values and earlier obsei \ ed arrival dates over the period of record. A regression plot of these data (Figure 2) produced r = Using a standard baseline date of 30 January, B. Fairfield-Carter (personal communication) conduct- ed a parametric a
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