Jonathan L. Atwood
Figure 1. North American population trends of Barn Swallow, by state and province, based on USGS Breeding Bird Survey data, 1966–2017 <https://www.mbr-pwrc.usgs.gov/>, scale = states; Sauer et al. 2017).
Anticipating field research on important conservation topics may seem far removed from the many challenges of the Covid-19 pandemic. Yet Mass Audubon’s conservation science department is planning a couple of specific projects that may be of particular interest to Bird Observer readers. These projects—on Barn Swallows and American Kestrels—will begin in April 2021, and we hope to have results that can be reported here sometime in the fall or winter.
Barn Swallows (Hirundo rustica) belong to a suite of aerial insectivores that are undergoing serious population declines in northeastern North America. Although a common, widespread species that occurs throughout most of the world, U.S. Geological Survey (USGS) Breeding Bird Survey data (Sauer et al. 2017) indicate that, over a 45-year period (1970–2014), the overall population of this species in the United States and Canada has decreased by an estimated 38% (Rosenberg et al. 2016). The Canadian population has declined approximately 80% since 1970, leading the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) to assess the Barn Swallow as Threatened (COSEWIC 2011).
Population trends within the Barn Swallow’s North American range vary geographically (Figure 1). Numbers are increasing in the southern tier of states from Arizona east to North Carolina. All of the Canadian provinces, California, and northwestern, midwestern, northeastern, and mid-Atlantic states generally show declining populations—with trends that are less pronounced in the Midwest. In Massachusetts, based on 29 Breeding Bird Survey routes, there has been an estimated 1.1% annual decline in abundance of Barn Swallow from 1966–2017 (Sauer et al. 2017). These declines were not reflected by Massachusetts Breeding Bird Atlas data, which showed a stable or increasing state-wide breeding distribution between the two atlas periods (1974–1979 and 2007–2011), although Walsh and Petersen (2013) nonetheless commented that the species merited “further monitoring and conservation action.”
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