BULLETIN FLORIDA STATE MUSEUM


adapted Stage IV species such as the Centurus woodpecker, Amazona
parrot, and vireos? At the time that each form invaded these islands,
did each undergo a taxon cycle beginning in a marginal habitat and
ultimately become associated with the mature limestone forest? Con-
temporary data do not support such a possibility. Rather David Lack
(in litt.) appears to have a more plausible explanation to the effect that
potential colonists on nearby islands would have to be best adapted to
conditions on the Cayman Islands. For example, the Amazona parrot
on the Caymans is especially characteristic of limestone forests (Table
8); on Cuba its conspecific is found in remote woodlands from mountains
to sea level. Elaenia martinica, so widespread and abundant in the
Caymans, is adapted to arid lowland woodlands elsewhere in the Carib-
bean region. Mimocichla plumbea of Cayman Brac, Cuba, and Hispani-
ola is a bird of forested regions, plantations, and gardens. These and
other examples strongly support the contention that colonization of new
islands is not necessarily restricted to Stage I species but could be suc-
cessful for species in any taxon cycle stage, provided they were pre-
adapted to and could find suitable ecological conditions on a new island.

 HABITAT DISTRIBUTIONS OF INSULAR AND MAINLAND
 BIRD POPULATIONS
 The extent to which breeding bird species occupy all habitats avail-
 able to them has been discussed at least in part by MacArthur and
 Wilson (1967, Chap. 5). Clearly, some combination of competition,
 predators, immigration, vegetational complexity, and other factors play
 significant roles in restricting bird species to given habitats. In some
 insular avifaunas that have been investigated intensively (e.g., those of
 Puerto Rico) individual bird species have undergone an ecological ex-
 pansion into many habitats, whereas species in the Panamanian tropical
 forests are much more restricted to a small number of habitats. As a rule,
 if an avifauna can specifically occupy all or most of the habitats avail-
 able, it can be described as eurytypic or "generalized;" if the species
 occupies only a small number of available habitats, it can be considered
 stenotypic or "specialized."
 Some interesting figures emerge from the habitat distribution of the
Grand Cayman avifauna. Considering seven upland terrestrial forma-
tions (Tables 3-10), the distributions of the 24 species occurring therein
(exclusive of the wide-ranging Barn Owl and Nighthawk) are as follows:

 1 species, in only 1 formation
 5 species, in only 2 formations
 5 species, in only 3 formations
 5 species, in only 4 formations


Vol. 19, No. 5