Luke's Birding Pages
Brown Booby, Sula leucogaster
February 1, 2003
Princeton Harbor, San Mateo County, California
These photos are from about 150 yards away, backlit, and through my scope on a windy day. Photos © 2003 by Luke W. Cole.
Gerry
Weinberger and I tried for the Brown Booby at Princeton Harbor today.
After unsuccessfully searching the jetty for it for some time, and driving
around the far side of the harbor to scope the jetty from the backside, also
without success, we had some lunch. After lunch, we tried again, and this
time had nice looks at the booby's head as it hunched down behind the rocks on
the jetty, and occasionally had full-body looks at the bird when it would hop up
onto the top rocks. Note that the lighting is so poor on the full body
photo that the white belly barely even shows up. We were some ways away
(~150 yards?), viewing through a scope at up to 50x, with the bird badly backlit
but still easy to observe. It preened throughout the 15 minutes we watched
it, after which it appeared to tuck its head and disappeared completely from
view behind the rocks.
Description. From my fieldnotes (see below for original fieldnotes with sketch):
Warm brown head and neck, into breast, sharply demarcated at breast with white belly. Solid yellow sulid bill, yellow facial skin along bill, dark eye, bluish? around [and in front of] eye, feet pinkish when backlit by sun when scratching head.
Additions from memory and photos: Warm brown back with no visible change in color from head and neck.
Diagnosis. This booby is distinguished from other sulids by its brown head (ruling out adult white-phase Red-footed Booby, adult and immature Blue-footed, Masked, and Nazca Booby, and adult and immature Northern Gannet) and its white belly (ruling out immature, and adult dark phase, Red-footed booby). Further distinguished from immatures in the Masked/Nazca complex by the extent of brown into the breast and the lack of a lighter cervical collar; Masked/Nazca I would also expect to have a heavier bill (particularly distally) and black, not blue and yellow, skin around and in front of the eye.
Analysis. By its yellow bill I initially judged it to be an adult; after gentle prodding by several others who have had better looks, and after studying some far better photos on Joe Morlan's webpage (http://fog.ccsf.cc.ca.us/~jmorlan/broboo.htm), I think that the breast color (which I did not see well) makes it a sub-adult. By the bluish patch in front of the eye I would tend to think it a male.
-- Luke Cole, February 1, 2003; revised Feb. 17, 2003.
Original fieldnotes:
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