Washington

Migratory birds in North America have specific needs depending upon the season, and require the flora and fauna they co-evolved with. Breeding for migratory songbirds is dependent upon the explosion of insects in spring and early summer, especially Lepodoptera species, in the northern parts of the continent. The birds migrate from Central and South America to the northern US and Canada to take advantage of that seasonal abundance. Those insects, in turn, are utterly dependent upon the plant species with which they co-evolved. This has been exhaustively researched and is well documented.

Migratory birds need fruit with a high fat content as they prepare for fall migration. In North America, native shrubs and trees produce fruit with a high sugar content in the spring and summer and a high fat content in the all. Many exotic shrubs and trees from Asia and elsewhere produce berries with a high sugar content in the fall. Yes, the birds will eat them, but they are not getting the nutrition they need.

The exotic plants compete with the native plants for resources, and drive the native plants from landscapes because the exotic plants have few or often no natural enemies in North American ecosystems. Birds that eat the berries of those exotic plants then spread the seeds, aggravating the problem.