challenge: What is the migration pattern of the yellow-bellied elaenia population in Veracruz and Oaxaca, Mexico?
  
  A. They migrate south of the Isthmus of Tehuantepec in winter
  B. They migrate to Central America in summer
  C. They migrate north of the Isthmus of Tehuantepec in winter
  D. They are year-round residents and do not migrate
  Answer: 