There were two or three candidate Townsend’s Storm-Petrels seen at the 30-Mile Bank and The Corner during the 15 July pelagic trip, as well as several very likely dark-rumped “Chapman’s” Leach’s. When the shared eBird lists for the trip went out a couple days later, we thought it most prudent to list them all as Leach’s/Townsend’s at the time but then see what light all the added photos might shed. Several of the birds indeed look good for Chapman’s Leach’s. And a white-rumped bird at the Corner looks good for a Townsend’s. See photos by Marky Mutchler in https://ebird.org/checklist/S145056434 currently listed as storm-petrel sp. but likely soon to be elevated to Townsend’s. Another bird seen that day at the 30-Mile Bank and photo’d by Nick Thorpe, which he currently lists as storm-petrel sp., looks like a potential candidate for a DARK-rumped Townsend’s–a morph which I am still too timid to have claimed in the field myself.
Camera-wielding participants on that boat should re-study their storm-petrel photos from those locations and see if they have any potential matches for inclusion.
The problems I typically have with IDing Townsend’s (vs. Leach’s) Storm-Petrel in the field is that there are 6 or 7 potential characters to use in such an ID, but I typically see birds that fit perhaps four or five of those characters but NOT the other one or two. Those characters favoring Townsend’s are:
–slightly smaller and darker
–clean(er) white rump
–broader white rump feathering, which is wider than the distal dark tail
–slightly shorter and rounder wing
–weaker pale carpal bar
–shallower tail fork
–more direct flight (but storm-petrel flight style is notoriously variable depending on wind and on what the bird is doing)
In fact, several of these features seem to vary somewhat with time, angle, lighting, photo processing, etc., so some views and photos of a particular bird looks good while others of the same bird look less good!
–Paul Lehman, San Diego