By: Bryan Watts
There are few things in life more thrilling than solving a good mystery or finding the answers to long held questions. For the third consecutive winter, CCB biologists have mounted an intensive push to answer a long list of questions as part of a consortium focused on the life cycle of the Ipswich sparrow. The consortium includes the National Park Service, Parks Canada, the U.S. Fish and Wildlife Service, Dalhousie University, Acadia University and The Center for Conservation Biology. The long-term goal of the group is to collect the information needed to build an integrated population model that may be used to better understand the vulnerabilities of this unique population and as a future management tool. Partners to the north have worked for years on fleshing out breeding ecology and more recently on migration pathways. CCB has focused on quantifying parameters from the winter season needed for the population model and questions pertaining to winter distribution.
Ipswich sparrows spend the winter on the wild edge where the Atlantic Ocean meets land. They are the true dune birds and have evolved in this constantly changing environment where their plumage blends in perfectly with the open sand and tones of mid-winter vegetation. Bird watchers have been intrigued by them for generations. Of all the savannah sparrow siblings, Ipswiches are like the peculiar but utterly fascinating uncle who lives isolated in a cabin on the mountain. Most birders get an occasional glimpse of them as they run into vegetation, flush a flock over to the next dune ridge or hear their faint calls from the dune grass. Maybe it is their enduring mysteries or the unique place where they spend the winter that is so engaging to the birding public.
During the 2019-2020 winter season, CCB biologists continued to capture and color-band Ipswiches along mid-Atlantic beaches and resight them to quantify winter survival. They conducted a longitudinal survey from North Carolina through Cape Cod to examine distribution and collected locations from transmittered birds to explore movement patterns, habitat use and the size of winter home ranges. Due to their open habitat, Ipswiches are difficult to capture. Over the past three winters, CCB has captured and color-marked close to 400 individuals within several field areas and conducted surveys to resight them through the winter. The team has also conducted scores of line transect surveys using distance sampling to estimate densities across a range of sites and conditions to explore factors that might contribute to distribution.
After a long pull up a steep grade, we are beginning to crest over the ridgeline with the winter ecology of Ipswiches. Ipswiches prefer pristine dune systems and are significantly impacted by improper coastal development. Ipswiches occupy a disturbance-successional niche that is several years past storm disturbance, likely due to the time it takes to develop enough plant cover to produce an adequate seed crop. Seed production along the coast is both spatially and temporally variable and this variation drives sparrow distribution. The use of beach grass to build and stabilize dunes is an effective management strategy to create winter habitat. Age ratios during the winters we have worked are biased to hatching-year birds. Year to year variation in winter numbers appears to be driven by the hatching-year class, suggesting that cohort strength may drive variation. Overwinter survival has been high during the winters we have worked. The center of abundance along the Atlantic Coast is Assateague Island and densities drop moving both north and south of this location. Rather than moving throughout the winter, most individuals arrive on Assateague Island and establish stable winter home ranges.
Ipswich sparrows are perched precariously on the dunes along the Atlantic coast. They are on the front line of coastal change and subject to all the insults that human expansion and climate change have to offer. Understanding their needs throughout the annual cycle is a first step toward effective management.