Ano Nuevo Island
San Mateo County, California
29 June 1998
Large white booby, standing on the marine terrace just below the right hand blind. I judged it to be about 20% larger than nearby Western Gulls and about half the size of nearby Brown Pelicans. The bird was immaculate white with contrasting black remiges, tertials and rectrices. The legs and feet were gray, including the webbed toes. The bill was long and cone shaped and dull yellowish or yellowish-green in color. There was a black patch on the face at the base of the bill encompassing the eye and extending slightly over the top of the bill and down to the chin.
It was a big-headed, big-billed and big-necked bird. The tail was pointed, but rather truncated and not as long as I anticipated. After viewing the bird for about 20 minutes from 8:15 am to 8:35 am, the bird flew off the rock and headed out to sea. I was able to watch the bird flying for about five minutes until it disappeared over the ocean into the distant western horizon. At no time did it plunge, although once it hovered a bit as if intending to plunge. The flight was rather labored, with heavy flapping to gain altitude followed by graceful curved glides down close to the water. It looked a bit like an overgrown Snow Goose as it flew off. I felt the flight style was more gull-like than I expected.
During most of the observation, while the bird was on the island, it was awake and preening actively and standing in an alert manner. I was able to get good views of the spread wing while it preened and later in flight. The wings were all white, except for the black trailing edge which included all remiges and tertials extending inward all the way to the body. I also looked for and did not see any dark wrist markings on the underwing. Red-footed often has such a mark while Masked lacks it.
I made another trip to Ano Nuevo Point in late afternoon, 11 July 1998 and saw the bird again. This time the bird remained on the island, preening only occasionally and eventually it put its head under its left wing and appeared to go to sleep.
This is the third Masked Booby I have seen in California. The first was an adult 22 June 1992 at the Salinas River Mouth, Monterey County and the second was a subadult at the Pt. Mugu Naval Station in January 1997. Photos of the latter may be viewed at http://www.californiabirds.org/photos/mabo.html.
There was some dispute about the age of the Ano Nuevo bird with some thinking it might not be fully adult because of it's gray legs and feet. However gray legs and feet are perfectly normal for adults of Pacific populations.
A Guide to the Birds of Mexico and Northern Central America by Howell and Webb (1995) states that this species has the bill yellow; except in the more southerly S. d. granti in which the bill is pinkish orange in adults orange-yellow by the 2nd winter). These two forms breed together usually mating assortatively at Revillagigedo and Clipperton Islands off Mexico. Thus some taxonomists have suggested that these two forms may deserve to be split into two separate species.
This split was formally proposed by Pitman and Jehl in "Geographic Variation and reassessment of species limits in the 'Masked' Boobies of the Eastern Pacific Ocean" (Wilson Bull. 110(2), 1998 pp. 155-170). These authors recommend the the orange-billed birds be called Nazca Booby (Sula granti) while all other populations remain Masked Booby (Sula dactylatra). Nazca Booby breeds only on the Galapagos, Malpelo, San Benedicto and Clipperton islands. It also tends to range closer to shore than Masked Booby. Nazca Booby is also smaller than Masked Booby with shorter legs, but has longer wings and tail than Masked Booby.
These authors also synonomize the northeastern subspecies of Masked Booby, formerly designated S. d. californica with S. d. personata including other eastern Pacific forms except for Nazca Booby. I believe that all three birds I've seen in California, including the Ano Nuevo bird, can be referred to Masked Booby, S. d. personata because of the generally dull yellow coloration of their bills. A summary of the situation is in the 20th report of the California Bird Records Committee (Western Birds 28:117-141, 1997)
Identification of immatures remains problematic. According to the 15th report of the California Bird Records Committee (Western Birds 25:1-34, 1994) first year birds may be distinguished by the deep chocolate brown color of Masked Booby rather than the decidedly gray coloration of immature Nazca Boobies. Pitman and Jehl (1998) further suggest that first year Nazca Boobies lack the white neck ring of first year Masked Boobies. The validity of these characters require further research.
I'd like to thank Don Roberson, Joseph Jehl and Bert McKee for supplying references, reprints and additional information.
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