By Stu Mills, CBC News Ottawa, July 25, 2019
Record-setting high water levels on the Ottawa River this spring and a period of unusually hot weather in the final weeks of June — not poisoning — are the likely causes of a die-off of ring-billed gulls in the Britannia neighbourhood.
Ted Cheskey, a bird conservation expert with Nature Canada, said flooding this spring kept most of the traditional nesting areas for a gull colony under the waves of the river.
"Before I jump to a conclusion that there's some pollution-related factor, malfeasance or something, [I would call it] part of the natural cycle in a very unusual year," he said.
https://www.cbc.ca/news/canada/ottawa/ring-billed-gulls-dying-ottawa-river-britannia-1.5223573