Headaches are a common symptom of some rare conditions and diseases. Among the rarer conditions that have headache as a symptom is the virus usually called "bird flu."
Avian influenza is a virus that is usually associated with birds raised on poultry farms or with birds sold live at market. It can occur in any species of bird, but is quite rare among people. Transmission between humans is even rarer.
Unless you live or travel extensively in certain countries, most people are at very low risk of acquiring bird flu. If you have been exposed to avian flu risk factors, and you have headaches or any of the other symptoms of bird flu, contact a doctor.
For more information about bird flu, read up on 12 fast facts about the virus.