Numerical responses of red-winged blackbird populations to changes in regional land-use patterns.

The Agelaius phoeniceus population in SW Quebec more than doubled over 1966-1981, apparently in response to increased corn production. In SW Ontario less pronounced increases in blackbirds and corn production also occurred. Although larger blackbird populations have been responsible for greater crop damage, the increased availability of waste corn during the spring and summer (breeding season) was likely most important in allowing the blackbird population to grow. Although corn production explains much variation in the size of blackbird populations, other factors such as the availability of breeding habitat and the spatial distribution of habitats (landscape heterogeneity) may be responsible for additional variation. -from Authors