Dr. Martin suggests that not only do invasive species have unique traits, but that individuals at the leading edge of an invasion have special traits that make them different from individuals of the same species living in areas that have been settled for a longer time. House sparrows (Passer domesticus) invaded New Jersey 150 years ago and invaded Panama only 30 years ago. How is the feeding behavior of the Panamanian birds different from that of the New Jersey birds?.