Pettingill (1970) defines a species as a “population, or populations of mutually fertile individuals reproductively isolated from individuals of other populations and possessing in common certain characters which distinguish them from any other similar population, or populations. If cross-breeding of two species occurs, the offspring are often sterile.” Species are distinguished by taxonomic characters not shared with any other groups.
Author: Thomas A. Imhof
Volume Number: 36 Year Published: 1989
Issue Number: 1
Page Number: 10
Link to article: http://birdlife.aosbirds.org/1989/Vol 36 No. 1_1989_p10-12.pdf
Link to the full issue of BirdLife: http://birdlife.aosbirds.org/1989/Vol 36 No. 1_1989.pdf