At Conowingo Dam, on the Catwalk, 02/27/99, 8AM-6PM, 3 Species of Gulls Ring-billed Gull ~10,000 Herring Gull ~300 Great Black-backed Gull ~90 Mystery Gull - The first-winter mystery gull(Herring?/Thayer's?) from last weekend is still around. While at first glance this gull resembles a Thayer's, it has many more Herring characteristics. Thayer's Characters: *The primaries, secondaries, and tail band are pale tan much paler than the "average" Smithsonianus Herring. Herring Characters: *Outer and inner webs of primaries are the same color; On Thayer's outer webs should be darker than inner webs. *Outer and inner webs of secondaries are the same color; On Thayer's outer webs should be darker than inner webs. *Primaries on standing gull do not show pale edges. *In flight, tan primaries, secondaries, and tailband seem to be just slightly darker than the mantle; on Thayer's primaries, secondaries, and tailband should be the same color as the mantle. *Head much paler than body; this is very common in Herring; I have not noticed this in the first-winter Thayer's I have seen. Thayer's or Herring Characters: *Rounded head - Thought of more commonly with Thayer's than Herring, but small, probable female Herrings can have rounded-looking heads. *Mostly black bill, slightly pale at base - Thayer's generally are thought to have all-black bills, Herrings generally extensively pale-based bills. Generation Schedule: 0700-0930 no turbines running 0930-1000 7 small 1000-1200 7 small, all large 1200-1725 2 small 1725-1740 6 small 1740-1800 6 small, 4 large (When the 4 large turbines were opened, visible gull numbers jumped from less than 1000 to ~25,000; Unfortunately there was little light left for observations, but it was impressive. There was a report that the Slaty-backed Gull was seen in the afternoon on the river by some observers scoping from the downstream parking lot (near the entrance to the Wildflower Trail). I cannot confirm this. Gene Scarpulla Towson, Maryland gscarp@erols.com