JOHNSTON: CAYMAN ISLAND AVIFAUNA


such an analysis for the three Cayman Islands has been undertaken, a
summary of which appears in Table 18. There appears, first of all, to be
only a weak correlation between feeding ecology and early stages of the
taxon cycle, namely that the presumed recent colonizers (Stage I) are
mainly either frugivores or omnivores. On the other hand, other char-
acteristically frugivorous birds, plus some insectivores, have also been
classified as Stage IV forms. As a rule, specific feeding ecology cannot
be closely correlated with a stage in the taxon cycle, at least for the
Cayman Island avifauna. There is, unfortunately, no available informa-
tion on food habits of Mimocichla ravida and Icterus leucopteryx, the
two recently extinct birds from these islands, although it is certainly true
that if this study had been made 40 or more years ago, both of these
birds would have been in Stage IV using the criteria of Ricklefs (1970).
Both were known, for example, to be quite restricted in habitat prefer-
ences and areal distribution on Grand Cayman.
 Some problems arise in subjectively assigning a given bird species to
 a given stage in the taxon cycle, especially as regards Stage IV. Ricklefs
 (1970: 475) gives this definition: "The last stage of the cycle, before
 going extinct or recycling, is the endemic population. As the cycle pro-
 gresses, populations move from marginal coastal habitats into more
 central and montane habitats." Similarly, Ricklefs and Cox (1972: 195)
 note: "Finally, descendant populations, often subspecifically or specifi-
 cally distinct, are restricted to small refugia." The problems in diagnosing
 taxon cycle stages for the Cayman Island avifauna condense to two major
 points. First, as described previously, these islands have neither montane
 habitats nor discreet small refugia, unless in the latter case one considers
 the mature, more-or-less inland limestone forests. Second, these three
 islands currently have no endemic species of birds, but, according to
 Bond (1956) and Johnston et al. (1971), do contain 13 species with
 endemic subspecies. It is of interest to recall that earlier taxonomists
 (for example, Cory 1886) regarded seven of these as distinct species.
 Based upon the contemporary belief that these (see Table 18) are all
 well-marked, distinct subspecies, endemic to one or more of the three
 islands, I am tentatively assigning the 13 forms to Stage IV in the taxon
 cycle. Their occurrences on the individual islands were outlined earlier
 by Johnston et al. (1971).
 Taxon cycles for the Caymanian avifauna may be compared, albeit
 with some qualification, with those of Jamaican birds (Ricklefs 1970) and
 Solomon Island birds (Greenslade 1968). Although the Cayman Islands
 currently contain no endemic species, Jamaica does have 26 such species,
 many of which (a) occur in the interior montane forests and (b) are in
 Stage IV. Ricklefs (1970) gave 14 as the number of Stage IV endemics,


1975