Anthropogenic changes to the landscape have both positively and negatively impacted nesting Bank Swallows. Bank Swallows readily use human-made nest sites, such as sand pits, road cuts, and soil stockpiles, but these gains have been offset by losses of natural habitat along rivers and seacoasts. Additionally, human-made sites tend to be ephemeral, while natural sites provide longer-term habitat. Bank Swallows are adapted to transient habitat, but within limits. For example, a river naturally meanders within its floodplain, eroding some areas, while depositing sediment in other areas. The locations of these areas of erosion and deposition change over time. This is the longer-term habitat to which Bank Swallows are adapted.

 

Many river systems in which Bank Swallows have historically nested are now heavily manipulated for energy production. This changes the erosional characteristics of rivers; to counteract these changes, bank erosion control projects are often undertaken and habitat for Bank Swallows is thereby lost. For example, Bank Swallows are state-listed as Threatened in California, primarily due to erosion control projects along the Sacramento River. Similar trends are occurring in other U.S. states and in Europe.

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Connecticut River Bank Swallow Project: Western MA, 1997-1999, 2018

 

In Western MA we have seen major losses of Bank Swallow nesting habitat in the Turners Falls Power Pool of the Connecticut River over the last 20 years, as a direct result of an erosion control project.  This stretch of river is 34 km in length. The pumped storage facility there, now owned by Eversource Company, commenced operations in the Pool in 1972. These operations increased erosion; as of 1991, approximately one-third of the banks of the pool were actively eroding. This increase in erosion led to a consequent increase in Bank Swallow habitat; in 1999 there were six active colonies in the Pool totaling over 1000 nesting pairs, with 80% of the pairs nesting in one bank (demonstrating how colonial Bank Swallows are) (see Silver and Griffin 2009). However, since 1999, bank stabilization efforts to mitigate erosion have led to the elimination of almost all of these nesting banks. When the pool was surveyed in 2018, we found only one active Bank Swallow colony with approximately 80 pairs (this is a 92% decrease in number of breeding pairs since 1999). The bank stabilization project was carried out using a technique called “bioengineering,” which involves grading a bank and stabilizing it with materials such fabrics, logs, stone, and plantings. This type of treatment can supply habitat for other bird species, but is essentially a desert to nesting Bank Swallows.