These Storm-Petrels were photographed
on a pelagic off the southern Texas coast on July 16, 2004
by Andy Garcia; the default species in this part of the
Gulf is "Band-rumped" Storm-Petrel - probably of the undescribed form now known as Grant's S-P, while Leach's Storm-Petrel Oceanodroma leucorhoa is much rarer. More images of these same birds can be seen here: http://texaspelagics.com/photo-gallery/BRSP/source/28.htm and then forwards in the gallery.
A note about Moult: according to Steve Howell's Tubenose book, wing molt for Grant's should take place between Feb - Aug with 2CY birds perhaps about 4 - 6 weeks earlier. Off North Carolina in late May and early June 80-90% with P6 - P9 growing, and most with 3-4 old outermost primaries; tail moult Jul-Aug. For Leach's the wing moult starts Aug/Oct and ends Feb/Apr, often with suspension during late Fall; 2CY birds start May/Jul and end Oct/Dec; tail moult May-Oct.
The pics are presented and "numbered" in the sequence
they occurred on Andy's camera - those without comment are ones
I feel unable to make much of!:
B looks to me to be a fairly classic Band-rumped type:
C1 seems to have too much white on the rump/utcs for Band-rumped?:
is D2 a Leach's?:
D3 is quite enigmatic to me: the white rump/utc patch appears
to be huge - much longer than the trailing dark patch formed by
the tail; the white on the rear-underside seems way too extensive
for Leach's (check the reflection) and there is no dark "point"
laterally where the all-dark outer retrices of Leach's normally
cuts into the wrap-around white; the tail does not look forked
enough for Leach's but tail moult/wear may be affecting the appearance; It is possible that the tail is angled downwards relative to the rump, thus artificially shortening the tail length:-
G looks like Leach's to me: extensive wear in the flight feathers;
little white underneath; "U"-shaped white rump patch
with hint of gray central divide; a dark "point" formed
by the black bases to the outer tail feathers, that splits the
white wrap-around; outer tail feathers much longer than inners
- there clearly seems to be two generations of tail feather:
H may the same bird as G?:
J looks like a classic Band-rumped type: narrow white rump patch; extensive
white below, with no dark splitting the wrap-around (Band-rumped
has white bases to the outer tail feathers and this white is on
BOTH sides of the basal shaft on the outermost - unlike Wilson's
which has a black outer edge and extensive white inner edge);
note that this bird does not seem to have badly-worn outer primaries
(see below):
pics K - N are probably the same individual; with 3 old outer Ps the moult would be quite early for a 2CY Leach's yet rather late for an older-age Grant's (which look like this in late May off NC); the extent and pattern of the pale ulna bar favors Leach's while the extensive white on the lateral undertail coverts and the rather shallow tail fork favor Grant's...:
