By: Chance Hines
Ipswich sparrows make their home in the coastal dunes of the mid-Atlantic where CCB has studied them since the mid-2000s. While the bulk of our efforts have focused on the nearby coastal areas of Virginia, we have also surveyed as far north as the massive wind-swept dunes along Massachusetts’ Cape Cod and as far south as North Carolina’s Outer Banks. These efforts have shown that that the wild dunes along the Atlantic barrier islands of Virginia and southern Maryland appear to support the bulk of the winter population.
Each project undertaken by CCB answers important questions about the sparrow’s ecology, but also leads to new questions. Past research efforts have focused on unveiling the Ipswich sparrows’ migratory pathways to and from their breeding grounds on lonely Sable Island, determining the extent of the species winter range, examining winter mortality through capture and recapture efforts and examining the influence of plant distribution on sparrow densities.
The current subject that the Center’s investigation is the Ipswich sparrow’s diet. Ipswich sparrows, like much of the nominate Savannah sparrow population, depend almost exclusively on seeds during winter. Unlike their nominate Savannah sparrow cousins, Ipswich sparrows are found in a habitat with relatively few plant species. The plant species that Ipswich sparrows depend upon during winter must be hardy enough to tolerate the wind, salt spray, and occasional wash over events associated with life in coastal dunes.
American beach grass has long been thought to be a staple of the species diet. Seminal work by Stobo and McLaren in the early 1970’s identified areas with this plant species as providing adequate forage. American beach grass is also widely planted in beach restoration efforts because it stabilizes dunes and is thought to provide food for a variety of species. However, Ipswich sparrow densities along CCB survey transects are more often positively associated with the occurrence of forb species like seaside goldenrod (Solegado sempervirens), poor joe (Diodea teres), and beach primrose (Oenothera deltoides) rather than American beachgrass. Radiotracking efforts have shown that some birds primarily use areas with abundant beachgrass but others do not. The results of these studies suggest that there may be some habitat segregation occurring within the species. Larger, more dominant individuals seem to occupy areas where both grass and forbs occur, while smaller and less dominant birds were more likely to use areas where either forbs or beach grasses were less available. Despite inhabiting a relatively open environment, their mousy and secretive behavior make it difficult to gather direct observations of their foraging behavior. Fortunately, recent advances in DNA technology allow the analysis of bird diets through the analysis of fecal samples. CCB is currently collecting samples in collaboration with the National Parks Service at Assateague Island National Seashore, hoping to further illuminate what plant species are most important to Ipswich sparrows. The results of this study could inform future management efforts and promote the inclusion of forb species in beach plantings to better provide winter food for Ipswich sparrows and other animals inhabiting the dunes.