Birds have a reputation as excellent parents. They expend a great deal of effort in building nests in which to lay their eggs. They patiently incubate the eggs, keeping them warm and safe until they hatch. Birds also bring food to their newly hatched offspring until the baby birds are independent. However, some unusual birds, known as brood parasites, don't provide any parental care for their young. Perhaps the most famous brood parasite is the cuckoo. Instead of building a nest, the cuckoo lays her eggs in the nest of another species with similar-looking eggs. The female cuckoo simply removes an egg laid by the host female, lays her own egg, and then leaves, expecting the host bird to care for the imposter. What is the main idea of the passage?