Two concepts of subspecies: an observation

According to modern rules, subspecies do not overlap in distribution; if they do, the two populations ought to be regarded as different species. In numerous cases, the status of a form has been changed solely because it has been recorded in the area inhabited by another population. This is considered a poor concept, sometimes leading to the paradoxical situation in which two subspecies are morphologically more different than two species. The author points out that, in tropical and subtropical regions, the same bird species might have — and frequently does have — two or more populations with different breeding cycles (spring, autumn, and winter). These populations can belong to the same form or be only subspecifically different. Therefore, it is recommended not to hastily elevate a form from subspecies to species status merely because of general geographic overlap