It is the grassland ecosystem which supports nesting Merlins on the Canadian prairies. This study considered the effects of some factors interfering with processes in operation in the natural functioning of the grassland ecosystem that influences Merlin populations. An important part of this study was the comparison of selected habitat features near Hanna, Alberta, where a segment of the prairie Merlin population continues to nest, and those near Kindersley, Saskatchewan, where Merlins once

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... ed but no longer are present. Additionally, data on nesting ecology of Richardson's Merlins were gathered along the South Saskatchewan River, and near Hanna, in southern Alberta, during the summers of 1968-1974. The absence of nesting merlins near Kindersley appears to be related to changing human land use patterns in that area. Since 1951, 62% of the land near Kindersley has been cultivated, while the comparable figure near Hanna, where Merlins continue to nest, is 26%. Air photo study of territories around Merlin nest sites showed that 52.3% of the area presumed to have been used by Merlins for hunting in the Kindersley area came under cultivation since the 1940's, as compared to 25.5% for the Hanna territories over the same period. Interpretation of 40 Merlin territories in use since 1971 in the Hanna area, has revealed that Merlins were hunting in areas which averaged 78% grassland. Increase in cultivation in both areas since the early 1960's has been about 7%, leaving Kindersley Merlin territories with less than 42% grassland by 1971. Assuming that at least 50%, grassland is required within a Merlin hunting territory in order to provide sufficient small bird prey, it was concluded that the Kindersley area has not been a prime Merlin nesting area since the 1940's, and that increases in cultivation since the early 1960's has probably reduced grassland below the threshold necessary to support nesting Merlins. It is felt that the heavy use of dieldrin in the early 1960's probably had the effect of administering t [...]