Conowingo Dam: 02/27/99

Eugene J. Scarpulla (gscarp@erols.com)
Sun, 28 Feb 1999 00:16:57 -0500 

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