Bird brain?

Joe is studying a course on Ornithology which is the study of birds. The time comes for his important final exams.

He goes home and spends the whole night memorising all his textbooks and notes.

The following day he goes into the exam hall fully prepared and confident. He sees 10 stuffed birds on the table and each of them has a sack covering its body leaving just its legs showing.

His professor then says,"Now students, i want you all to look carefully at the legs of all the birds on the table and correctly label the common name of each and every one. You may begin now."

Joe looks hard at those legs. But no matter how he looks at them he still cannot figure out what kind of birds they are. He is so frustrated and angry that after 20min he yells, "That's it! This is ridiculous! I am leaving!"

His professor is shocked by his outburst and calls out to him,"Wait! What is your name?"

Joe turns around and angrily lifts up the leg of his trousers and said,"Now YOU tell me!"