Here are my notes from earlier today.  They were compiled after both sightings had occured.  
 
Martin sp. (Brown-chested?) 10/29/06 Hafner and Holbrook
 
First sighting:
about 9:30am
Seen behind the Maintence Yard flying east of the field to the south, then turned north (so we were looking directly into the sun) and dipped down below the trees along Rt. 611.  Closest viewing distance was ~100 feet when I first spotted it.  Total viewing time ~10 seconds
 
Immediately notices the larger size and different shape from the thousands of Tree Swallows in the area.  The Martin was more elongated, with longer wings, a more forked tail, and a head that was more pointed.  Both wings were molting inner primaries, a feature that I did not see on any of the Tree Swallows.
 
My best view of the underside was when I first saw the bird and the lighting was still not ideal.  It appeared to me that the throat and upper chest were dusky.  There was not a sharp demarcation between the markings and the white underside.  Also, the white underside was not nearly the gleaming white of the Tree Swallows it was much "dirtier."  When I first saw the bird, I was looking for the "Bank Swallow" pattern that I had seen in field guides for Brown-chested Martin (knowing it was a likely candidate), but what I actually saw seemed more like a Rough-winged Swallow underside.  The underwings were dark.
 
After the bird emerged from being backlit and right before it dipped below the trees, we had a great view in good light of the upperparts which were all flat brown.  It lacked the collar of a Purple Martin.  
 
Second sighting:
about 10:15am
First seen from boat ramp parking while bird was flying over Verrazano bridge parking lot, silhouette only.  Immediately called Hans and ran across the street where we both had views in better light.  Unfortunately not better views of underside.  Closest viewing about 50 yards when the bird was flying past the south side of the Visitor Center with the sun behind us.  Total sihouetted viewing ~15 seconds, good light viewing ~10 seconds.
 
First noticed from >200 yards by distinctive shape and molting inner primaries.  When I crossed the street and got the sun behind me, the martin banked giving me another excellent view of the all brown upperside.  As it flew away with a few twists and turns, had obvious markings in upper chest/throat area, but I was unable to discern any pattern or detail.  Again the white underside was not nearly as bright as nearby Tree Swallows.  
 
My main question to those with experience is: Does Brown-chested Martin always have a distinctive Bank Swallow type chest pattern?  Can the chest pattern appear diffuse and have some markings on the throat?  What are the other options for a "brown" Progne?  Are there any inconsistencies with Brown-chested Martin in the description?
 
Any help you can provide would be appreciated.
 
No matter what the answers to the above questions, Jim Stasz and I will be at the visitor center at 7am tomorrow morning hoping it returns.   
 
Matt Hafner
Bel Air, MD
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