Although the erodibility of these banks leads to the loss of some nests, the advantage is that this is a hard place for raccoons and other predators to get a meal. Once hatched, the nestlings are fattened on insects and, early August the parents and offspring gather by the thousands to begin a long migration back to South America where they overwinter. Eventually the river bank it will either collapse and form another steep bank for next year's colony, or if the river stops cutting here, it will become covered with vegetation. Bank swallows evolved the flexibility to shift from one nesting area to another. Typically the new nesting ground is found in the same stretch of river, but can be several miles away.
Banks erode, beaches form, floodplain forests develop, only to be eroded again centuries later.
This beautiful and dynamic system of shifting habitats is critical to the survival of many of our specialized plants and animals. Make a map that shows the shoreline of Glacial Lake Hitchcock in your community. The Northampton Oxbow is a famous historic example of a river loop that was cut off. Other birds nest in river banks. At first glance it may seem that stabilizing an eroding bank with rock or other debris would always be a good idea.