The turning off of the sewer outflow at Pier 17 in St. John's in June 2015 was like turning off the life line for Black-headed Gulls and Common Gulls in Newfoundland. In an average winter 75-100+ Black-headed Gulls over wintered at the Pier 17 sewer outflow. Sometimes counts reached 150 during migration in November. And Pier 17 has always been the best location in North America for Common Gull with 1-3 overwintering with a half dozen or more different birds going through there per year.
We knew the result was not going to be good after turning off the tap, but somehow we hoped the Black-headed Gulls would find away around the loss of the main source of food at Pier 17 and still be around for us in St. John's. NOPE! It didn't happen. It is all about the food. Shut down the only restaurant in town and the costumers will go elsewhere. Where they all went we still don't know. We never really noticed the Black-headed Gulls come into town and leave again. A handful was all we ever saw at once during the fall of 2015 in St. John's. The St. John's CBC tallied a desperate TWO Black-headed Gulls, the lowest total by far since St. John's CBCs started in the 1960s.
Black-headed Gulls depend heavily on sewer outflows in winter in Newfoundland. The stretch of shoreline from Spaniard's Bay to Carbonear used to be as good or better for Black-headed Gulls than St. John's back in the 1980 and early 1990s but then they started their sewer outflow manicures. Mainly they piped the raw sewage out in to deep water where the goodies were inaccessible to Black-headed Gulls but just fine for the goldeneye and scaup. Black-headed Gulls disappeared from this area as well except for Spaniard's Bay where there is a limited tidal mud flat. Here BHGUs can feed in a more natural way - but just a few.
Other locations on the Avalon where Black-headed Gulls can feed in a natural way on tidal mudflats are Bellevue Beach and Arnold's Cove. These areas support fewer than a dozen individuals in winter per location. The occasional Black-headed Gull will try to make a winter living at other locations around the Avalon - Renews,Trepassey, Branch.
The last sewer outflow on the Avalon that is any good for Black-headed Gulls is at Chamblerlains, Conception Bay. This has a small flow and can not support many gulls. I was at the Chamberlains sewer outflow today during lunch break. The 14 Black-headed Gulls was probably the most I've ever seen there in any year. It was good to see them but even better to see a Common Gull. This place is scheduled to shut down in the fairly near future as well. How rare will Black-headed Gull and Common Gull become in Newfoundland!??
Below are photos from today (28 Jan 2016) at Chamberlain's focusing on the Common Gull. Note the mirror on the three outer most primaries. Common Gulls regularly have a mirror on Primary 8.