BULLETIN FLORIDA STATE MUSEUM


Cayman Thrush (Mimocichla ravida), although the species was observed
and collected by ornithologists over a span of some 50 years. Contem-
porary data on breeding seasons of birds of the Cayman Islands are
summarized in Table 13, the data having been derived from the scanty
literature, from my own experiences, and those of Donald W. Buden who
spent five continuous months on Grand Cayman in the spring of 1970.
 A number of features in Table 13 merit special mention. Sula leuco-
gaster shows a bimodal breeding season, a characteristic of this species
well-known from several previous reports on other islands (Schreiber and
Ashmole 1970). Tyto alba, although not studied in detail throughout the
year, clearly shows some peak of breeding activity in mid-winter. Mimus
polyglottos, from fragmentary observations and reports, has a protracted
breeding period in the spring. Coereba flaveola apparently breeds in
every month of the year.
 The annual breeding cycles of land birds on the Cayman Islands con-
form generally to Immelmann's description (1971: 348-9): "Most birds
of regions with a regular change between one long dry and one long wet
season per year . breed around the rainy season with only a few spe-
cialists laying during the dry period." In Table 13, it is evident that peak
breeding on the Caymans is in May and June; in each of these months 54
percent of the land birds are breeding and, for June, 55 percent of all
the breeding species. By referring to Table 1, it can be seen that this
peak in breeding activity coincides with the onset of the wet season.
Tentatively, then, it would appear that rainfall is an important proximate
factor in regulating breeding, a conclusion similarly reached by Snow and
Snow (1964) for Trinidad. Obviously, the wet season (May-October)
is the period in which resident birds should reach their highest annual
population densities and should make their greatest demands on food
resources. Quantification of food resources was not made in this study,
but it is quite likely that the wet season is a time of maximum food
availability. The quantitative report by Dingle and Khamala (1972: 220)
at African localities is relevant here: "Most savanna and dry country
birds breed during the long rains; this breeding is correlated with a major
increase in the availability of insect food." (On the other hand, as
discussed later, the dry winter months must also be a season of abundant
foods, especially small insects, to support the influx of North American
migrants, many of which glean insects from leaf surfaces in the mangrove
and limestone forests.)
 The "specialists laying during the dry period" (Immelmann 1971)
 should more properly be called generalists in this sense, especially if they
 breed during both dry and wet seasons. Among the Cayman avifauna in
 this category are Crotophaga ani, Tyto alba, Coereba flaveola, and prob-


Vol. 19, No. 5