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.
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.
Bank Swallow colony, Turners Falls Pool of the Connecticut River, 1998, before bioengineering (stablization of bank).
Former Bank Swallow colony, Turners Falls Pool of the Connecticut River, 2001. Photos show the process of "bioengineering." The bank is no longer habitat for nesting Bank Swallows.
This example indicates the need for long-term planning on projects of this scale. This is especially important at present because of the requirement of the power company to relicense its facilities. We are conducting surveys and supplying data to organizations involved in relicensing so that Bank Swallow habitat conservation can be considered in future management activities.
North Brookfield, MA Solar Project: 2018
As solar energy expands, solar companies seek locations for large projects. We were called on when a solar company sought to install a PV solar array in a sand pit adjacent to an active Bank Swallow colony. The owner of the sand pit had been accommodating the swallows for years by excavating the sand pit to create vertical nesting banks. The local Conservation Commission was concerned about the future of the colony when the solar company proposed building an array in the sand pit. We drew up a management plan that allowed enough space in front of the Bank Swallow colony to provide a buffer between it and the solar array, and to allow access of machinery to continue to excavate the banks to maintain them for the Bank Swallows. We also requested the solar company access road be placed at the end of the bank with the least swallow activity. We will continue to monitor the site.