Summary
We compared aspects of eastern kingbird (Tyrannus tyrannus) breeding biology between lakeshore and upland habitats in eastern Ontario. Nests were more closely spaced and eggs were laid earlier at the lakeshore than in the uplands. Within the lakeshore habitat, nests were more likely to be placed on small islands (< 0.2 ha) and eggs were laid earlier there than on large islands or the mainland shore. Kingbirds nesting in lakeshore habitat had some advantages: (i) moderated temperatures for nests placed low over water, (ii) more efficient foraging when feeding nestlings, and (iii) faster growing nestlings, relative to upland nestlings. However, upland nests fledged more young than lakeshore nests. Within lakeshore habitat, small island sites had the highest breeding success. With the exception of nest site location, which differed markedly between habitats, differences in breeding biology and behaviour between the two habitats were small. A lack of substrate specificity in foraging, together with an ability to use a range of nest sites, apparently allow kingbirds to nest successfully in a wide variety of habitats.
Methodology
Study area
The study was conducted at the Queen's University Biological Station (44O32' N, 76O19' W), 50 km north of Kingston, Ontario, during the spring and summer of 1977. The biological station is situated at the southern edge of the Canadian Shield, an area characterized by numerous small lakes, wetlands, and rocky terrain. Studies of kingbirds in lakeshore habitat were confined to Lake Opinicon, a shallow (< 10 m deep) eutrophic lake 9.5 km long and 2.0 km wide. The presence of more than 50 islands and many small bays results in a total shoreline length of approximately 60 km (determined from aerial photographs). A low density of cottages is present around much of the lake but in most cases shoreline trees have been left standing. A few areas near the lake have been cleared for pastures and hayfields.
Much of the area surrounding Lake Opinicon is unsuitable for farming because of the rocky landscape and presence of wetlands. Hayfields, pastures, and abandoned fields constitute most of the upland habitat available to kingbirds. Since most of these upland areas are adjacent to roads, it was possible to obtain a representative sample of nesting kingbirds by driving 50 km of country roads within a 10-km radius of the biological station. Upland areas suitable as nesting habitats were found along all but 10 km of these roads.