The Rise and Fall of Ring-Billed Gulls (Larus delawarensis) in Eastern North America
2016
Giroux, Jean-François | Patenaude-Monette, Martin | Lagarde, Florent | Thiériot, Ericka | Brousseau, Pierre | Molina, Pierre
Ring-billed Gulls (Larus delawarensis) were rare at the beginning of the 20th century, possibly because of intensive exploitation. Once they became protected in 1916, their numbers increased throughout eastern North America, reaching a maximum of 875,000 breeding pairs around 1990. Since then, an overall decline of 19% has been recorded in the Great Lakes and the St. Lawrence River while their numbers tripled in Atlantic Canada. The largest concentrations are still found on the Great Lakes with 38% and 42% of the birds breeding in Canada and the USA, respectively. The remaining individuals breed along the St. Lawrence River (15%), on Lake Champlain (2%), and in the Gulf of St. Lawrence including the Atlantic Provinces and Saint-Pierre-et-Miquelon (3%). In 2009, a study was undertaken in the largest colony located on Île Deslauriers near Montreal, Québec, to determine the factors that regulate the number of breeding birds. This colony supported 52,000 pairs in 2000 and 44,000 in 2012. Ring-billed Gulls had a lower reproductive output in 2010–2012 compared to the late 1970s attributed to reduced chick survival. The number of gull-days at the nearest landfill declined from 906,000 in 1995 to 40,000 in 2012 following the implementation of a falconry deterrence program. Limited access to an abundant food supply located near the colony may have reduced chick survival. How this affects annual survival and population size remains to be determined. In the long term, policies that aim to reduce input of organic matter at landfills and discourage citizens from feeding gulls could further contribute to the decline of Ring-billed Gulls in eastern North America.
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