Thanks to the generous cooperation of David Willard and the Field Museum of Natural History, Chicago in late February 2009, I was able to examine the Chaetura specimens in their collection. While doing some comparative study I examined a tray of 139 pelagica, looking at each specimen individually. I noticed a dramatically darker skin that seemed out of place, but the collection data (Chicago window kill, June 2001) strongly indicated that it was indeed a pelagica, and no basic measurement was outside the range for that taxon, so at this point the presumption is that this is a dark-form pelagica - possibly melanistic:-
Here is at the top of the middle row of skins:
here at the right end:
here at the bottom of the left row:
