The American Coot breeds from North America south to northwestern South America and, in recent years, has been documented breeding in the Greater Antilles and northern Lesser Antilles south to Guadeloupe, where it appears to be expanding its range. The Caribbean Coot breeds in the Greater Antilles, Lesser Antilles, Curacao and western Venezuela. The two forms are currently regarded as specifically distinct but reports of mixed pairs and intermediate individuals in the northern Caribbean suggest that they may be conspecific. The degree of clinal variation and assortative mating has not been thoroughly investigated. The variability of these taxa, which has been discussed by Clark (1985) and more thoroughly by Roberson and Baptista (1988), is discussed in this photo essay. Coots possess a 'shield' that represents an extension of the maxilla onto the forehead. The size and shape of the shield vary seasonally and is often swollen in both sexes during the breeding season. In some species a fleshy 'callus' represents an accessory atop the shield. American Coots typically possess a small white shield extending to the eyes or halfway between the eyes and crown, with a large reddish or brownish callus. Caribbean Coots typically possess a large white shield extending to the crown; the shield is sometimes tinged yellow and the callus is absent. Thus, any coot with a red callus can be assumed to represent an American Coot. However, up to 1.5% of American Coot males with high testosterone levels possess a large frontal shield with a reduced callus that may even be absent. Such individuals were intitially thought to represent Caribbean Coots but are now regarded as variants of American Coot (there are no satisfactory North American records of Caribbean Coot) essentially indistinguishable from Caribbean Coot. Thus, identification of white-shielded male coots in the potential range of overlap is problematic. Males of both species average larger than females. American Coots are proportionately longer winged and shorter legged than Caribbean Coots, but much overlap occurs. Intermediate appearing individuals possessing a large white shield with a vestigial callus occur throughout North America, where hybridization obviously does not occur. Whether or not such intermediate birds in the northern Caribbean represent hybrids or variants within either taxon remains uncertain. Such individuals should be documented even though their specific identity may be uncertain. Roberson and Baptista (1988) used the following categories for scoring shield type variation in coots:
A = normal American Coots with typical red callus B = 'intermediates,' with red callus but washed with yellow on shield below callus, some having a very reduced callus C = bulbous shields strongly washed yellow, sometimes with reddish splotches D = bulbous white shields, with obvious reddish spots, streaks, or splotches, but not a callus E = bulbous white shields with little or no reddish staining, limited (if present) to extreme upper edge of shield (i.e., normal Caribbean Coot)
These categories should be adopted by observers of coots in the Caribbean. Seemingly mixed pairs should be studied to determine the sex of each individual, if possible. Males should be larger and mount females. Both sexes participate in nest construction, incubation and parental care.
LITERATURE CITED
Clark, C. T. 1985. Caribbean Coot? Birding 17:84-88. Roberson, D., and L. F. Baptista. 1988. White-shielded coots in North America: a critical evaluation. American Birds 42:1241-1246. |