Caribbean Coot Fulica caribaea (found sparingly and locally in the West Indies from Hispaniola south and east to the coast of Venezuela) is virtually identical to American Coot except for its all-white frontal shield (Roberson and Baptista, 1988). ((The claim by Brisbin and Mowbray (2002) that American and Caribbean coots can be distinguished by the “shield being continuous with bill in Caribbean Coot, while in American Coot, shield is formed by a callus, which is distinct from bill ” is not true. This may be a misinterpretation of Gullion (1951), who says that the shield of all coots is a continuation of the bill, and is white, and that American Coot and some other species differ in having a red “callus” structurally distinct from the shield and covering the upper part of the shield.)) The fact that some American Coots in North America lack the callus and have all-white shields makes identification of any potential vagrant Caribbean Coot in North America impossible, and calls into question the validity of Caribbean Coot as a species.
Are they from the Caribbean?
Caribbean Coot was first reported in the US in 1974 when Wally George took note of a white-shielded coot in Fort Lauderdale, Florida. Subsequent detailed scrutiny of coots revealed white-shielded birds – six additional birds in southeast Florida within six weeks of the first (Bolte, 1974). In the following years more were found, and soon doubts were raised when ‘Caribbean’ Coots were found in Texas, Tennessee, California, and British Columbia. Singles paired with typical American Coots and raised young in Michigan (Payne and Master, 1983) and Indiana, and one was found wintering in Florida that had been banded in the summer in Wisconsin! Roberson and Baptista (1988) summarize all of these records and conclude that there is no evidence to support a Caribbean origin of any of the white-shielded coots in the US.
Gullion (1951) showed that testosterone levels influence the size and shape of the shield in coots, and that the shield is largest on males from just before spring migration through the early part of nesting activity, shrinking gradually as breeding season winds down. In fact, virtually all reports of white-shielded coots in North America fall between January and July. I have found white-shielded and intermediate coots many times simply by watching a flock for the most aggressive individual, and then focusing on that bird. Based on behavior and other clues most, and possibly all, of the white-shielded coots recorded in North America have been males.
Regional differences (or lack thereof)
Roberson and Baptista (1988) estimated the frequency of occurrence of white-shielded birds in California at about 1.4%, which was slightly higher than the frequency reported in Florida (less than 1%). The difference could be merely the result of different thresholds for classifying a bird as “white-shielded”, or the fact that the California study methodically surveyed coots for this feature and Florida numbers were exact counts of white-shielded birds but post hoc estimates of the total number surveyed. In any case these results show that Florida does not host a higher percentage of white-shielded coots than elsewhere.
In The Sibley Guide to Birds I stated that the enlarged white frontal shield is found “more often in the south”. This was based on my impression that I saw white-shielded coots more often among the relatively small numbers of breeding coots in Florida, southern Texas, southeastern Arizona, and California than I did among the larger numbers breeding in the north. Roberson (in litt.) has questioned that statement, pointing out that most white-shielded coots have been found in the wintering flocks in places like California, Texas, and Florida, and migrate somewhere farther north to nest.
This is certainly true, and there may not be any regional variation in frequency of white shields, but I still have the impression that white shields occur in a significantly higher percentage of the coots nesting in the southernmost US (and maybe also along the Pacific coast) than in the north. A careful survey of breeding coots in those places would be instructive.
Is Caribbean Coot a good species?
Since white-shielded male coots occur throughout North America, the conclusion that these birds are merely variants of American Coot (and not visitors from the Caribbean) is inescapable. Furthermore, since the white shield is the only feature that defines the species known as Caribbean Coot, there is no way to identify a Caribbean Coot with certainty, even in the hand. I’m not aware of any genetic work on these populations, but with no diagnostic differences in appearance it seems doubtful that Caribbean Coot is a distinct species. As Clark (1985) says it is disconcerting to think that “the status of Caribbean Coot as a species should hinge upon so tenuous a characteristic”. Both white- and red-shielded coots and intermediates occur together in the Virgin Islands and elsewhere in the West Indies, apparently interbreeding freely there (see Hayes). Gill (1964) studied a similarly variable group of coots in the Andes and concluded that they were best considered a single species, dimorphic for shield color. It seems likely that the coots of the West Indies represent a similar situation.
Bolte, W. 1974. Caribbean Coot, Fulica caribaea, in Florida. Am. Birds 28:734-735.
Brisbin, Jr., I. Lehr and Thomas B. Mowbray. 2002. American Coot (Fulica americana), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/697a
Clark, C. T. 1985. Caribbean Coot? Birding 17:84-88
Gill, F. B. 1964. The shield color and relationships of certain Andean coots. Condor 66:209–211. http://elibrary.unm.edu/sora/Condor/files/issues/v066n03/p0209-p0211.pdf
Gullion, G. W. 1951. The frontal shield of the American Coot. Wilson Bull. 63:157-166. http://elibrary.unm.edu/sora/Wilson/v063n03/p0157-p0166.pdf
Hayes, F. Identification Essay: American Coot (Fulica americana) and Caribbean Coot (F. caribaea). Internet post accessed Mar 2011. http://secrb.trinidadbirding.com/idamericancaribbeancoot.html
Payne, R. B. and L. L. Master. 1983. Breeding of a mixed pair of white-shielded and red-shielded American Coots in Michigan. Wilson Bull. 95:467-469. http://elibrary.unm.edu/sora/Wilson/v095n03/p0467-p0469.pdf
Roberson, D. and L. F. Baptista. 1988. White-shielded coots in North America: a critical evaluation. Am. Birds 42:1241-1246. http://elibrary.unm.edu/sora/NAB/v042n05/p01241-p01246.pdf
Photos of recent white-shielded coots from Washington can be seen at these websites: