Change in wing morphology of the European starling during and after colonization of North America

When exposed to a new area and the potential for range expansion, species may quickly evolve morphological traits that allow them to colonize novel habitat. How quickly these changes occur and how long they subsequently persist in the established population has rarely been documented in birds. The European starling has been introduced in a number of areas around the world, including North America where an initially small population was established in 1890 and 1891. Their prolific expansion westward across the continent occurred at a tremendous rate of up to 90km/year. We hypothesized that the individuals leading the expansion wave had longer and pointier wings because these characteristics are associated with greater juvenile dispersal distances. Therefore, we predicted that successive generations of range expanding birds would display increasing wing length and pointedness. Using museum specimens collected in North America since their introduction, we tested this hypothesis and examined temporal patterns to determine if wing shape changed following the establishment of local populations after the initial colonizing phase. Contrary to our expectations, wing length and shape did not change during the colonization wave. However, the pointedness of European starling wings decreased across the continent by more than 3.8% over the last 120 years. This was caused by an increase in the length of the secondary feathers, not by a decrease in the length of primary feathers. We discuss these results in the context of increased afforestation and urbanization during that time, and the potential benefit of rounder wings for foraging and predator avoidance.