It's often stated that birds have no sense of smell, but this probably hasn't been carefully tested. It must be admitted that some birds probably don't; owls eat skunks from time to time, and if someone told me that an owl has no sense of smell, I would have to believe it on this evidence alone.
Behavioral studies on chickens indicate that they identify items as "food" by size and color, not taste or smell. On the other hand some species of buzzards definitely locate their food by means of smell. Pipeline companies use this bit of natural history to locate breaks in gas pipes. They put an odorant into the suspect line that contains cadaverine, a breakdown product produced in the decomposition of flesh. They then wait a day or two and find the spot above the line where the vultures are hovering in greatest numbers, and there is the break!
You pay your money and take your choice in this debate; there are almost certainly species-specific differences.
