Patterns and causes of change in a cliff swallow colony during a 17-year period
The number of cliff swallow (Petrochelidon pyrrhonata) nests at a farmstead in southeastern North Dakota increased at an average annual rate of 87% with house sparrow (Passer domesticus) removal during 1957-60 and 1970-72. Harassment of nesting cliff swallows by house sparrows, adult swallow mortality from cold weather in late May, and collapse of nests were the principal observed factors limiting swallow population growth during a 17-year period.
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