. The Canadian field-naturalist. 520 The Canadian Field-Naturalist Vol. 101. Figure 1. Location of the study area and the magpie roosts in central Edmonton, Alberta. In Edmonton, magpies are found mostly near the North Saskatchewan River (Figure 1). The adjacent river valley is km wide, 50 m deep, and consists mainly of steep wooded slopes and flat open spaces. White Spruce {Picea glauca) and Trembling Aspen {Populus tremuloides) are the main tree species in the valley. Some Balsam Poplar {Populus balsamifera) and Paper Birch {Betula papyrifera) are also present. The main shrub species
. The Canadian field-naturalist. 520 The Canadian Field-Naturalist Vol. 101. Figure 1. Location of the study area and the magpie roosts in central Edmonton, Alberta. In Edmonton, magpies are found mostly near the North Saskatchewan River (Figure 1). The adjacent river valley is km wide, 50 m deep, and consists mainly of steep wooded slopes and flat open spaces. White Spruce {Picea glauca) and Trembling Aspen {Populus tremuloides) are the main tree species in the valley. Some Balsam Poplar {Populus balsamifera) and Paper Birch {Betula papyrifera) are also present. The main shrub species are Hazelnut {Corylus cornuta), Chokecherry {Prunus virginiand), Pincherry {Prunus pensylvanica), Thinleaf Alder {Alnus tenuifolia), and Wild Rose {Rosa acicularis). The study was restricted to the south side of the river between Whitemud Creek and Mill Creek (Figure 1). From November 1983 to April 1985 I followed magpies from their daytime ranges to their roosting sites. Twelve roosts were found (Figure 1). I noted the behaviour of the magpies as they arrived at the roosts in the evening and departed from them in the morning on numerous occasions throughout the study. Two of the roosts were in well-delimited deciduous thickets (see results). I estimated tree density in these roosts with the point-centered quarter method (Cottam and Curtis 1956), using a total of 21 sampling points along seven equidistant parallel transects (three points at 10-m intervals on each transect line). Only trees over 2 m high were considered. The four trees used at each sampling point were also measured for height and DBH (diameter at breast height). Height was measured with an Abney level. Nine roosts were in well-delimited coniferous stands on the slopes of the river valley or adjacent tributaries (see results). All trees present in the stands and higher than 2 m were counted and measured for (1) height, (2) DBH, (3) number of lateral branches longer than 15 cm in the lowest 6 m, (4) number of nei
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