Nest-site selection and response to habitat manipulation by roseate terns (Sterna dougallii) on Seavey Island, New Hampshire

Burbidge, Susie
Jon Atwood, PhD
Department of Environmental Studies
In the Gulf of Maine, little quantitative research has been conducted on the nesting habitat requirements of Roseate Terns (Sterna dougallii), or responses of this species to differing types of vegetation management. I conducted habitat manipulations aimed at creating suitable Roseate Tern nesting habitat on Seavey Island, Isles of Shoals, New Hampshire, in late Apr - early May 2006. Study plots were located in areas that had previously supported Roseate Terns, but where increased vegetation density was thought to have inhibited their nesting in recent years. Habitat manipulations included (1) weed-whacking and hand-pulling of vegetation (handremoval) around rocks within each plot, or (2) application of an herbicide to remove vegetation from up to 50% of the plot. Roseate Tern nests were located closer to an opening and were surrounded by taller vegetation than associated random points. Nest sites were characterized by: (1) average vegetative cover > 65% within 0.5 m of the nest, (2) openings located < 0.20 m from the nest, (3) presence of a flat rock or boulder within 0.5 m of the nest, and (4) at least 44% of the nest cup obscured from above. In 2006, 10 Common Tern nests were found in plots treated by herbicide and 3 in plots where vegetation was removed by hand. Two Roseate Tern nests were found in the handremoval plots, 1 in the control plot, and none in the herbicide-treated plots. Habitat manipulations resulted in a shift from grass to herbaceous species in all of the study plots; plots treated with herbicide showed the greatest change. Hand-removal of vegetation seemed to provide good Roseate Tern nesting habitat, but was logistically difficult in terms of manpower and appropriate equipment. Herbicide and fire treatments conducted after the 2006 breeding season reduced vegetation cover from 93% in 2006 to 78% in 2007. This more open habitat was attractive to Common Terns, which increased in their overall population size between 2006 and 2007 from 2,463 to 2,539 pairs. The number of Roseate Tern nesting pairs on Seavey Island also increased between 2006 and 2007, suggesting that the habitat manipulation was beneficial. Fire may be a good management tool for a large tern colony, but careful consideration should be given to the timing and frequency of the burn. Continued management of the vegetative cover on Seavey Island is critical to enhance Roseate Tern habitat and increase productivity. These findings may be valuable at other breeding sites in the Gulf of Maine.