The challenge I particularly undertook in my research was attempting to present criteria for the identification of boobies of this type in juvenal or subadult plumages. Boobies do not begin molt for the first 6-8 months of life. The booby shown at right is in juvenal plumage -- no primary molt has begin -- and in his chocolate-brown dress looks superficially like an adult Brown Booby S. leucogaster. It is, in fact, a juvenal Nazca Booby. Note it already has a yellow eye (Brown Boobies are dark-eyed). It lacks the broad white cervical collar which is characteristic of most juvenal Masked Boobies, and this individual is already changing bill color. Both species start out with gray bills and both species eventually become yellow at the tip (see the top photo) so the important area is at the base of the bill. In Masked Booby this area gradually changes from gray to greenish-yellow to bright yellow; in Nazca Booby the base of the bill changes from gray to dusty-rose to pinkish-orange to bright orange or reddish-pink. The pale "dusty-rose" or lavender color of Nazca Booby can be seen in this shot (and presents an opportunity for you to determine whether your monitor has good color quality... ahem). [Additional discussion of juvenal Masked v. Nazca Booby identification is on line HERE with special reference to a bird on Monterey Bay in Feb 1999].
Boobies are strictly marine birds, feeding primarily on fish, and they
come ashore only to nest or roost. The three closely-related gannets (genus
breed and summer well beyond the tropics, but I have spent little time
in eastern North America, or southern Australia & New Zealand, or South
Africa, where gannets are common. [There was a gannet in the north Pacific
until the late Pleistocene, but I'm not quite that old.] In the tropics,
the most pelagic of all boobies is the Red-footed Booby (three next
photos, below). They come in a bewildering area of plumages, including
both white morph and dark morph adults (upper two shots below).
Immature birds, like the young Red-footed Booby perched on a dead Ridley's Sea-Turtle far offshore (left), is also extremely variable in pattern. Indeed, separating imm. Red-foots from imm. Brown Booby can be extremely difficult. The literature is devoid of information about the full range of variation, and I consider it one of the least appreciated field problems in North America today (even rarity committees rely on mistaken assumptions).
Identification topics aside, Red-foots are really cool birds because
they rely heavily on flying fish to survive. Often at sea, days away from
any land, we would have a cadre of Red-foots circling the ship, waiting
for us to flush a flying-fish into flight (below). They would then dash
after the glider, trying to snatch it before it resubmerged. Fun for all!
Not only is the identification of boobies a fascinating topic, but boobies
can present exceptional panoramas of abundant bird life. Examples include
islands full of Masked Boobies (below, upper photo of Clipperton Island
by Robert L. Pitman; a few scattered Brown Boobies are also present) or
the flights of foraging Peruvian Boobies (below, lower photo) off
the coast of Peru (along with a few Guanay Cormorants Phalacrocorax
another fun aspect of boobies is their vagrancy to California. Four species
(five species if my theories about Nazca Booby are correct) have reached
the state; indeed, all four (or five) have reached Monterey County, my
home. My first experiences in California were with Blue-footed Boobies
(next two photos). Blue-foots appear in erratic, unpredictable "invasions"
which often begin at the Salton Sea [That's me at 19 years of age, with
Jolee DeLew, at Salton City -- we'd driven all night and most of the next
day to reach here, along with Wally Sumner, in my little red VW bug --
on my first really long "chase" trip in 1971.] There have not been such
wonderful invasions in the last 20 years; a good summary on those earlier
events are in McCaskie (1970).
Another huge invasion occurred five years later in 1976, and one Blue-foot wandered all the way up the Sierran foothills to New Hogan Reservoir, Calaveras County (the photo left is of that bird and me). This lost bird appeared 15 September 1976 and stayed a month; it was found dead in mid-October (Elliott 1976). For many years this was single species for Calaveras County (having failed to write down any common species that day)... a rather fine trivia question.
As a family, the various boobies are closely related. The name "booby" comes from a British seaman's slang for "stupid;" on nesting island the first sailors could walk right up to the birds and hit them over the head. [Indeed, keeping breeding islands free of people and introduced predators is a key to successful nesting in boobies.] Most of the species nest on the ground, as the Clipperton I. shot above shows, but the Red-footed Booby and Abbott's Booby Sula abbotti on Christmas Island in the Indian Ocean nest primarily in short bushes and trees. Birds do not breed until they are 2-6 years old, depending on the species. Boobies lack a brood patch (it would interfere with aerodynamics in flight) but, instead, have highly vascularized feet. Although birds on nesting islands seem to be sitting on their eggs during incubation (as do other types of birds), they are, in fact, warming them with the webs of their feet! A nice summary of booby biology is in Carboneras (1992).
Photos: The photo of an adult Nazca Booby Sula granti next to an adult Masked Booby Sula dactylatra was taken by Robert L. Pitman on Clipperton I. in May 1987; the few Nazcas among the thousands of Maskeds here usually mate assortative here, and it was unclear if these birds were paired [of course since the Pitman/Jehl paper appeared in 1998, the AOU (1998) had not yet split the taxa]. Three shots of Red-footed Booby Sula sula: the white-morph adult at sea at 19°N, 114°W, on 2 Aug 1989; the dark-morph adult hovering over its nest site at Kiluea Lighthouse, Kauai, Hawaii, on 28 Aug 1989; and an immature riding a dead Ridley's Turtle was at 9°12'N, 87°03'W, on 9 Nov 1989. The flying-fish was at 17°N, 112°W, in Aug 1989. Robert L. Pitman took the panorama view of nesting Masked Boobies Sula dactylatra in May 1987. The flight of Peruvian Boobies Sula variegata were in Paracas Bay, Peru, on 12 June 1987. The two vagrant Blue-footed Boobies Sula nebouxii in California were: Salton City on 6 Nov 1971 (with Jolee DeLew; photo shot by Wally Sumner with my camera) and New Hogan Reservoir 24 Sep 1976 (photo snapped by Donna Dittmann with my camera). Photos © 2000 Don Roberson except the two attributed to Robert L. Pitman who holds those copyrights (used with permission); all rights reserved, and none may be republished in any form without written permission of the photographer.
Family Book: III rating (out
of 5 possible)
Nelson, J. Bryan. 1978. The Sulidae: Gannets and Boobies. Aberdeen Univ. Stud. Ser. 154. Oxford Univ. Press, Oxford.
At 1012 pages, this is the thickest book I own! It was an attempt to set out, in leisurely detail, everything that was then-known about the boobies of the world. It is totally unlike any other family book -- it is intended to be and is a major research tool. Every species has a complete account of every nesting island, with long dissertations of breeding biology and ecology, and extensive details on behaviors (esp. breeding displays). A few color plates (photos) and many black-and-white photos are scattered throughout. It is an indispensable book for those studying this family.Literature cited:
And yet it is strangely unfulfilling. Although the plumage and soft part details are lengthy, there is no real attempt to get at questions of field identification. It does very little good to have a long list of bill or foot colors from the various populations around the world unless those details are tied down to specifics: at what age and in what population are the feet yellow versus green, etc., etc. Nelson seems to regurgitate everything that anyone has ever said about boobies without trying to sift the wheat from the chaff. In doing so, he overlooks those details that Pitman & Jehl (1998) would later use to show that the "Masked" Boobies on the Galapagos are a different species. The photos in Nelson's own book sometimes show important and definitive characters that are overlooked in the text (such as the lack of cervical collars on Galapagos juvenal boobies). And despite the huge length, there really is not nearly enough about the breeding phenology of each individual island population, details which could lead to new understanding of vagrancy. And their are no color plates aimed at side-by-side identification of species.
In its own way it is a wonderful book, and yet so much is lacking... one must turn to something like Carboneras (1992) for a field guide approach to the worldwide boobies (and then that text is rather weak on inter island populations, and totally overlooks the orange-billed boobies on the Galapagos).
American Ornithologists' Union. 1998. Check-list of North American Birds. 7th ed. A.O.U., Washington, D.C.TOP
Carboneras, C. 1992. Family Sulidae (Gannets and Boobies) in del Hoyo, J., Elliott, A., & Sargatal, J., eds. Handbook of the Birds of the World. Vol. 1. Lynx Edicions, Barcelona.
Elliott, B. G. 1976. Blue-footed Booby in northern California. W. Birds 7: 155-157.
McCaskie, G. 1970. The occurrence of four species of Pelecaniformes in the southwestern United States. Calif. Birds 1: 117-142.
Pitman, R. L., and J. R. Jehl, Jr. 1998. Geographic variation and reassessment of species limits in the "Masked" Boobies of the eastern Pacific Ocean. Wilson Bull. 110: 155-170.
Roberson, D. 1998. Sulids Unmasked: which large booby reaches California. Field Notes 52: 276-287.
(I wanted to call this "Boobies unmasked: the story of big boobies on California beaches" -- but the editors nixed that idea.)
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