White-Shielded Coots in North America: a Critical Evaluation
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POPULATION STUDY records of the Caribbean Coot Fu- BOLTElica caribaea(1974)REPORTED in North THEAmerica, FIRST seven white-shielded birds around Fort Lauderdale, Florida, from January 28, to May 9, 1974. Several were photo- White-shielded coots graphed and on April 2 an immature male was collected(National Museum of Natural History 567252). Identifi- in North America: cation was basedupon the broad, high, and bulbous frontal shield that lacked a red, corneous callus; in all other re- a critical evaluation spectsthe birds resembledthe American Coot F. americana. Bolte sketched the shieldsof all sevenbirds. Only two were wholly white. The shieldsof the other five (including the specimen) were marked variouslywith irregular,reddish patches, and three were washed with Don Roberson and various shadesof yellow. These 1974 birds were acceptedas the first records Luis F. Baptista for North America (A.O.U. 1983). Additional white-shielded coots were found in Florida in each succeeding winter, althoughskepticism soon arose. In the winter of 1974-75, Stevenson (1975) reported "a spateof 'Caribbean Coot' records from Florida." This led Figure I. TypeA, TypicalAmerican Coot. June 1978, Palo Alto, California/D. Roberson. Volume42, Number5 1241 some of us to suspectthat most, if not records of white-shielded coots and re- In this paper we follow nomenclature all, of thesewere merely aberrant Am. portedunpublished white-shielded birds of the A.O.U. (1983), which considers Coots showingthe variationsof shield in Texas duringthe winter of 1982, with the Caribbean Coot F. caribaea of the color and shapeknown in that species." photographs.Alan J. Ryff (in littO re- Antilles and northwestern Venezuela a Yet Caribbean Coots continued to be porteda white-shieldedcoot with a tiny separate species from the American reported annually in Florida, all ap- red spoton the high point of the shield Coot F. americana, the breedingbirds pearing during winter. In March 1985, at Reifel Island, Vancouver, British Co- of North America, although some au- a white-shieldedbird paired with a typ- lumbia, on October 6, 1984. Still an- thors already considerthem conspecific ical American Coot and remained to other white-shielded bird was studied (e.g., Roselaar 1980). American Coots nest near Tierra Verde, eventuallyrais- with American Cootsin May-July 1985 occasionallynests as far south as Flor- ing severalbroods (L. Atherton, in litt.). in East Chicago, Indiana, where it ida, and in the Bahamas and Greater Away from Florida, white-shielded eventuallymated with a typical bird. It Antilles. Recently birds showing the coots identified as Caribbean Coots was not thought to have Caribbean or- callus typical of the American Coot were reported from Chattanooga,Ten- igins (Peterjohn 1985). DeSante and have been observednesting with Carib- nessee,from November 1981 to Feb- Pyle (1986) rejectedmore northerlyand bean Coots at St. Maarten, Netherlands ruary 1982(Hall 1982,photo published; westerly records,but accepted records Antilles, and apparent hybrids have acceptedby A.O.U. 1983) and near De- for the Caribbean Coot in Florida. The been produced (Norton 1982). Similar troit, Michigan, in April-May 1982. National Rare Bird Alert (NARBA) re- mixed nesting has been noted in the The latter bird paired with a typical ported "confirmed" reports of Carib- Virgin Islands (R. L. Norton, in litt.). American Coot, nested, and raised at bean Cootsin 1986 from Florida, Texas, Many have suggestedthe two "species" least three young (Payne and Master Illinois, and Arizona (fide J. Mofian). representpolymorphism in the Amer- 1983). Payne and Master suggested,as A review of white-shielded coots in ican Coot (Ripley 1977; Payne and had DeBenedictis (1982) earlier, that North America is therefore warranted. Master 1983; A.O.U. 1983). A similar white-shielded birds in North America In the late 1970s and early 1980s, we situation existsin the Andes, where the simply representedsporadically occur- both independently observed white- two phenotypesare simply confidered ring morphs within northern popula- shielded, yellow-shielded, and inter- morphs of F. americana (Gill 1964) or tions of coots. Payne and Master con- mediate coots in California. We report separate species,F. americana and F. cluded that there was no evidence to here our findingsof variation in win- ardesiaca(Fjeldsa 1983). Likewisethe suggesta Caribbean origin for the tering populationsof coots in coastal Hawaiian population of F. americana Michigan bird. California and comment on their tax- alai has both morphs (Pratt 1978, Clark (1985) summarized published onomic significance. 1987),though in that population,white- shielded morphs are the commoner phenotype. Although our paper may have taxonomic implications, we wish primarily to proposean answerto two questions. Has the Caribbean Coot, whatever its taxonomic status, been documented to occur in North Amer- ica?Is there any evidenceto suggestthat white-shieldedbirds anywherein North America have Caribbean origins? In November 1983--January 1984, we surveyedcoots wintering on sdected small pondsin California. For the most part these were ponds where we had found atypical cootsin previousyears, though half were selected without knowing what was present. We rather arbitrarily divided the shieldcharacters observedinto five categories: A = Normal American Coots with typical red callus (Figure 1). B = "Intermediates," with red callus but washedwith yellow on shield below callus(Figure 2), somehav- ing a very reduced callus (Fig- ure 3). C = Bulbous shields strongly washed yellow, sometimes with reddish splotches(Figure 4). D = Bulbous white shields, with ob- Figure 2. TypeB, "Intermediate': November1983, San Francisco,California/K. Hansen. vious reddish spots, streaks, or 1242 American Birds, Winter 1988 splotches,but not a callus (Fig- ure 5). E = Bulbous white shields with little or no reddish staining, limited (if present)to extreme upper edgeof shield (Figures 6, 7). Although there is some subjectivity in assigningbirds to these categories, they provide a convenient means of quantifying the frequencies of the morphsin variouspopulations sampled. Our survey resultsare summarized in Table 1. These surveys indicate a fre- quencyof bulbous-shieldedbirds (types C, D & E) of about 1.4%, and a fre- quencyof atypicalbirds (typesB, C, D & E) of about 3%. Bolte's (1974) seven Caribbean Coots in Florida (out of ap- proximately 800 birds surveyed) fell into categoriesC, D & E, a frequency of 0.8%. Clark (1985) thought the fre- Figure 3. TypeB, "Intermediate".November 1986, Palo Alto, California/J. Morlan. quency of Caribbean-type birds in his surveysof Texas and Florida birds to be about 0.25%, but somewhat greater than 0.5% if "intermediates" (our type B) were included, The Ft. Lauderdale, Florida, Christmas Bird Count has re- portedsix CaribbeanCoots among 6910 coots over the past five years (1981- 1985), a frequencyof only 0.1%. These surveys suggest that Caribbean-type coots occur as frequently in California as in Florida. Apart from our findings, additional white-shielded coots have been reported in California away from the areasof our surveys:McGrath State Beach, Ventura County (completely white-shieldedbird, August 5, 1982; L. Atherton), Oakland (completely white- shielded bird, February 11, 1984; J. Morlan), Fresno (February 1984; K. Hansenflde J. Morlan), Palo Alto (two birds in November 1986; J. Morlan), and Santa Barbara (one white-shielded, one intermediate in November 1986; J. Dunn, R. Abbey,allper& comm.). Given our assumption that all Cali- fornia coastalbirds are American Coots, we questionedwhether any of the Flor- Figure 4. TypeC. December1983, Arcadia, California/D. Roberson. ida birds could claim true Caribbean origin. Florida birds with bulbous Table 1. Frequeucyof occurrenceof coot morphsfrom variousCalifornia localities. shields,like those in California, appear ShieM Type primarily in the wintering population Total from November to May (L. Atherton, Locale N A B C D E in littO and appear to show the same range of variation observedin Califor- Chain-of-Lakes, Golden Gate Park, San Francisco 134 119 9 4 1 1 nia birds. There is no empirical evi- Nearys Lagoon, Santa Cruz 86 85 0 0 0 1 denceto suggesta Caribbeanorigin for Los AngelesArboretum, Arcadia (one pond only) 19 17 1 I 0 0 Crespi Pond, Pacific Grove 121 121 0 0 0 0 any Florida bird, except for Bolte's Lake El Estero, Monterey 216 213 1 0 2 0 (1974) specimen. Therefore we com- Naval Golf Course, Monterey 116 116 0 0 0 0 pared the only North American puta- TOTAL 692 671 11 5 3 2 tive specimen of the Caribbean Coot Volume42, Number 5 1243 Figure 5. TypeD (center).November 1983, San Francisco,California/K. Hansen. Table 2. Measurement (in mm) of two taxa of Fulica: with 20 F. americana (ten males, ten femalesfrom California, Colorado, and Taxon Sex N Range )7 (+s.d.) sig.* Indiana) selectedrandomly from the WING collectionat the California Academyof Sciences,San Francisco, and 19 F. car- F. americana M 10 186-212 199.5 (8.96) F 10 185-209 194.4 (9.80) ibaea(ten males,nine femalesfrom the F. caribaea M 11 171-202 188.73 (9.15) P < .01 LesserAntilles and Haiti) from the col- F 9 164-197 176.89 (10.10) P < .005 lection of the National Museum of Natural History. CULMEN Males averagedlarger than females in all measuresin both taxa (Table 2). F. americana M l0 40.5-52.5 45.27 (3.82) F 10 36.6-54.6 43.58 (4.92) Male F. americana had longer wings F. caribaea M 11 46.6-57.8 52.43 (3.39) P < .01 than F. caribaea(199.50 versus188.73; F 9 42.8-51.3 47.24 (2.99) n.s. p < 0.01). Wings of female F. ameri- cana also were longer than wings of fe- BILL male F. caribaea(194.4 versus176.89; F. americana M l0 13.I - 16.8 14.89 (1.06) p < 0.005). The shorter wings of the F 10 13.7-16.5 14.95 (.95) Caribbean Coot may reflect the rela- F.