These are rather interesting birds and I am not so sure after reading about them that I like the idea of having them around. They say cowbirds historically would follow the bison, feeding off the insects that associated with the huge herds. Since their food source was mobile, these birds divised a way of raising a family without having to settle down. They would deposite their eggs in other birds' nests, they found other species would raise their offspring at the deterement of their own eggs. No longer capable of making their own nest, cowbirds rely completely on other birds to raise their young. They prey upon species that had no previous contact with them and thus have added another pressure to songbirds that are struggling to survive(Birds of Coastal British Columbia, by Nancy Baron & John Acorn).