A major landmark of our field season is the GOMSWG Census. GOMSWG stands for Gulf of Maine Seabird Working Group, and is a collection of professionals who pool their knowledge and efforts together to provide greater insight to the condition of our seabird populations. This census, which focuses on nesting Terns, occurs on many islands in the Gulf of Maine, and allows us to detect yearly variation in the density of nesting seabirds. Our census was completed yesterday after being rained out on Friday. We also took a day trip on Monday to Matinicus Rock to assist the Maine Audubon crew complete their census. We had a great time seeing a different island, and the hospitality was unmatched!
To census, a tight line of staff and volunteers progress through the colony and mark each nest with a Popsicle stick. Upon marking the nest, the clutch size (number of eggs) is shouted to the recorder, who shouts the number back in order to confirm that the correct number was recorded. Recording sounds very simple until there are 6 people shouting at the same time in a dense nesting area, and the entire process is being drowned out by the commotion of upset Terns.
Luckily the line stops and waits for the recorder. We don’t know how Charlie’s voice survived the recording process. After the colony is combed, the group walks two transects to count how many nests are marked vs unmarked. From this we can establish a correction factor estimating the number of nests we may have missed, and calculate a final population estimate for the season. Our final corrected population for this year is 498 nests, which is about two thirds of our population last year. Metinicus Rock’s numbers are up though, and they say they have read bands on several birds banded on Metinic. Hopefully this immigration accounts for our loss.
On Metinic we have a 30 meter grid system that covers the entire Tern nesting area. This grid not only keeps us on track as we progress through the colony for census, but by uploading nest numbers into a GIS database, we can monitor shifts in habitat use and nest density over the island. This information is crucial to tracking the effectiveness of management efforts. If a particular grid suffered from uncharacteristic levels of predation, are Terns as likely to nest within the same area the following year? If we manage vegetation by excluding the sheep from one area and instead mow the vegetation, does one provide more productive nesting habitat then the other? Considering these are question that take years to answer, the grid and census are the most viable means of answering them.