Songbirds have long been used to study vocal learning, because, like humans, they learn to imitate the sounds they hear from their parents in order to communicate vocally with others. In our case, we learn to talk, in the case of the birds, they learn to sing. Obviously, having an animal model for vocal learning is a powerful tool for understanding what happens in the brain that can lead to problems such as chronic stuttering or the difficulty associated with vocal learning in diseases like autism and other autistic spectral disorders. The problem with using songbirds to study these disorders is that they are absent, or at least extremely rare, in the songbirds. Animal models for lots of other human diseases have been created by genetically engineering mice, or fish, or frogs, etc. By adding or removing certain genes that are thought to be important for a particular disease, scientists can test how important that gene is, or they can find out what part of the gene may be involved. They can also use these "transgenic" animals to test other factors that may contribute to the disease if the disease is likely caused by both genetic and environmental factors (e.g. Parkinson's disease). Making transgenic animals usually involves injecting DNA into the nucleus of a fertilized egg, or injecting stem cells into the zygote when it is at a stage where it is still a ball of cells. This is obviously difficult to do in songbirds, whose eggs have a hard outer shell, that you can make a small hole in, but larger cracks tend to be fatal to the developing bird. Also, previous attempts to introduce DNA have run into unexplained difficulties. Now, however, it appears that those difficulties have been overcome through the use of a virus that has the capability to introduce genes into the cells it infects (known as a retrovirus). This technique was first used by Carlos Lois and Benjamin Scott at MIT to make transgenic quails (close relatives to the chicken). Now, Fernando Nottebohm and Robert Agate at Rockefeller University have figured out how to make this technique work in zebra finches. Here's the link to the blurb about this on Science Daily.
(Songbirds are awesome. And so is Fernando Nottebohm. The full article is to be in an upcoming edition of the Proceedings of the National Academy of Science, I will link to it when it becomes freely available.)