The Atlantic song sparrow (Melospiza melodia atlantica) was discovered in the dune and marsh edge habitats of the mid-Atlantic coast 86 years ago.
Its cousin, the widespread eastern song sparrow (Melospiza melodia melodia), occupied a variety of habitats just inland from the Atlantic song sparrow and is the familiar song sparrow in many eastern U.S. backyards today.
It is likely that the differences between the 2 subspecies were caused by adaptations to harsh dune and marsh edge habitats.
The eastern song sparrow is strongly associated with human settlement, but how the more specialized Atlantic song sparrow persists in the face of continued development on the mid-Atlantic coastal plain and coastline has been the focus of recent research.
In 2010, we studied variation in song sparrows from inland to coastal areas to determine if coastal populations are currently distinct. They are!
We also compared measurements from birds captured in the summer of 2010 to museum specimens collected an average of 91 years ago.
We took standard measurements in the field and analyzed color patterns using digital imagery. Digital imagery, not previously used to study geographic variation in birds, allowed us to develop quantitative data on plumage differences.
We found that coastal populations have:
- larger bills
- less rusty plumage
- more distinct black markings on the upperparts
Plumage pattern and bill size differences were found in both the recent and historical samples indicating the differentiation may have remained stable over the past century of coastal development.
The Atlantic song sparrows measured in 2010 had larger bills and less black in their back plumage than the historical specimens, trends that need further investigation with larger samples from more areas of the subspecies' range.
Future research will focus on determining the width of the overlap zone, analyzing microsatellite markers to estimate the pattern of gene flow, studying song characteristics which are used for mate attraction and territory defense, and testing hypotheses for the adaptive significance of the features that distinguish Atlantic song sparrows.