Survey of Coastal Nesting Colonies of Cormorants, Gulls, Night-Herons, Egrets, and Ibises in Massachusetts, 2006-08

Melvin, Scott

This report summarizes results of a coastwide survey of colonial waterbirds nestingin Massachusetts that was conducted during May and June, 2006-08. Species surveyedincluded Double-crested Cormorant (Phalacrocorax auritus), Great Egret (Casmerodiusalbus), Snowy Egret (Egretta thula), Little Blue Heron (Egretta caerulea), Cattle Egret(Bubulcus ibis), Black-crowned Night-Heron (Nycticorax nycticorax), Glossy Ibis(Plegadis falcinellus), Laughing Gull (Larus atricilla), Herring Gull (L. argentatus), andGreat Black-backed Gull (L. marinus). A total of 96 known or potential colony sites,including all significant colony sites that were surveyed in the last comprehensive surveyin 1994-1995, were surveyed during May or June in 2006 or 2007. One additionalhistoric site, Clarks Island in Plymouth, was surveyed by boat on 5 June 2008.Additional counts of roof-nesting gulls at selected sites in 2006 and 2007 were reportedpursuant to depredation permits. Surveys at most colonies consisted of total nest countsmade by observers on the ground. At small rocky islands that were too steep for safelandings, counts of nests or nesting adults were made by observers in a small boat thatslowly circled each island. On South Monomoy Island, Chatham, nest counts were madealong systematic transects on all but the northern portion of the island. Mark-recapturenest counts were used to survey gull colonies on Tuckernuck, Muskeget, and Penikeseislands. Surveys at most sites used the same methodologies as in the previousMassachusetts survey in 1994-95 so that results would be directly comparable.Tallied in the 2006-08 survey were 5,963 pairs of Double-crested Cormorants at 31sites, 9,725 pairs of Herring Gulls at 55 sites, 9,054 pairs of Great Black-backed Gulls at49 sites, 1,492 pairs of Laughing Gulls at 1 site, 781 pairs of Black-crowned Night-Herons at 14 sites, 401 pairs of Snowy Egrets at 10 sites, 228 pairs of Great Egrets at 6sites, 144 pairs of Glossy Ibises at 5 sites, 17 pairs of Little Blue Herons at 1 site, and 2pairs of Cattle Egrets at 1 site. Comparisons of results from sites surveyed withcomparable methods in 1994-95 and 2006-08 indicated substantial decreases in numbersof pairs of Double-crested Cormorants (- 19.5 %), Herring Gulls (- 42.2 %), Great BlackbackedGulls (- 40.0%), Black-crowned Night-Herons (- 45.3%) and Snowy Egrets(- 36.0%). Species that had increased in abundance between the 2 survey periods wereLaughing Gull (+ 82.6%), Glossy Ibis (+ 193.0 %), and Great Egret (+ 230.4 %).The substantial declines observed in 5 of these species indicate a need for moreintensive monitoring and conservation-oriented research. Recent coastwide surveys inMaine and New Hampshire have documented similar declines in cormorants and the twolarger gull species (Welch et. al. 2010). Recommended actions include: 1) morefrequent monitoring of breeding populations, i.e., at least every 3 years, 2) research toimprove precision, accuracy, and efficiency of surveys, 3) a more thorough assessment ofthe trends reported in this report in the context of regional trends, and 4) research toidentify factors that are influencing state and regional trends in these species. Improvedmonitoring of breeding cormorant, gull, and wading bird populations is especiallywarranted given the vulnerability of these species to potential threats posed by sea levelrise and climate change.