Date: 7/27/26 11:01 am From: Tristan McKee via groups.io <atmckee...> Subject: [CALBIRDS] Tristram´s Storm-Petrel off Humboldt
This Saturday, 25 July 2026, Sean McAllister, Lucas Stephenson, Aidan
Brubaker and I photographed a Tristram's Storm-Petrel northwest of the Eel
River Canyon at 40.757332 N, -124.81674 W, about 28 miles offshore from the
Humboldt Bay. The bird flew straight at the side of the boat and wheeled
around almost overhead, circled a little more with somewhat bowed wings and
mothy wingbeats, and then headed off far to the east in a low, direct style
with rapid, fairly shallow wingbeats.
Identification criteria between this species and the Markham's Storm-Petrel
are poorly developed, since the two taxa normally are found nowhere near
one another geographically. This bird was somewhat worn in plumage and
likely a subadult; it was less extensively gray and with a darker rump than
in my experience with Tristram's in northwestern Hawaii or the Tristram's
that Lucas and others documented off Marin last July, and this led us to
seriously consider Markham's in the field. It was rather slender-bodied and
very long-tailed. However, after review of the photos and videos and
consultation with Todd McGrath, Logan Kahle, Ryan Terrill, Steve Howell,
Peter Pyle, Rob Fowler, and others, we have a strong consensus that it was
a Tristram's Storm-Petrel.
Key features indicating Tristram's rather than Markham's include a small
amount of pale mottling on the sides of the rump (easily visible in Sean's
photos but not mine), a short bill, and an exceptionally deep tail fork.
The leg length and foot size may be important as well, but I haven't yet
assessed how well this can be determined from photos (there is always the
problem that seabirds hold the hidden knee joint in variable positions,
altering field impressions). The flight style difference between the two
species in calm conditions like ours seems to be quite striking and can be
judged from videos; to my eye, Tristram's is reminiscent of a Lesser
Nighthawk, while Markham's recalls a Common Nighthawk. Howell also pointed
out that the lighter wing-loading of Markham's is characteristic of many
Eastern Tropical Pacific species when compared to North Pacific species
like Tristram's and Fork-tailed.
Compared to a Black Storm-Petrel, the short neck, thin bill, squarish head,
grayish back, carpal bars extending out to the forward edge of the wings,
thin body, and long, swallow-like tail made for a very striking bird. The
legs and feet in the photos also appear considerably smaller.
Tristram's Storm-Petrel is a central and western North Pacific bird that
was first documented in Calfornia at Southeast Farallon Island in 2006, and
since then, accepted records are comprised of another there in 2015, one
near San Nicholas Island in 2018, and one last year off Point Reyes. July
seems to be a good time for it. Markham's is a species of western South
America and the eastern tropical Pacific that has been recorded off western
Mexico.
Eel River Canyon is proving itself to be one of one of the best locations
on the west coast, for storm-petrels with flocks numbering in the
thousands, recalling the old days at Soquel Canyon. Saturday´s bird was a
bit further offshore, in the Leach´s zone, however.
