BULLETIN FLORIDA STATE MUSEUM


houses; T. caudifasciatus is common in wooded formations where it
consumes large insects and small vertebrates; Myiarchus is an inter-
mediate-sized woodland and "edge" species that is more generalized in
food habits (insectivorous and frugivorous) than the other species.
 VIREOS (VIHEONIDAE).-The three resident vireos of the Caymans
 proved difficult to analyze for interspecific ecological differences, and the
 present summary should be considered tentative. As is true elsewhere in
 the distribution of the genus Vireo where sympatry and/or syntopy are
 evident, the usual case is the presence of an arboreal member of the
 subgenus Vireosylva and a thicket-inhabiting member of the subgenus
 Vireo (Hamilton 1962). Presumably these stratal and perhaps other
 differences effectively minimize interspecific competition.
 Over the years of observations on Grand Cayman, however, it be-
 came apparent that V. crassirostris, although the only vireo inhabiting
 thickets and shrubby fields, coexisted with V. magister in early logwood
 successional stages. A similar relationship existed between V. crassirostris
 and V. altiloquus on the other two islands. Indeed, through the seral
 stages into a climax limestone forest formation, both forms could be
 found. Frequently both species were observed or collected in the same
 strata between 3 and 5 m. As a rule, V. crassirostris was most frequently
 encountered below about 4 m, whereas both V. magister and V. altiloquus
 tended to prefer foraging positions from 5 to 15 m.
 The relatively large number of stomachs examined (11 for V. crass-
irostris and 9 for V. magister) and taken at the same season revealed
food differences that (1) reinforce feeding strata differences and (2)
provide the key to avoidance of interspecific competition (see Appendix
III). V. crassirostris consumes a higher percentage (77%) of animal
food than V. magister (51% ). Probably the species of Coleoptera or
other taxa mutually eaten by both vireos were in fact different, although
the insect fragments found in their stomachs could not be identified be-
low the family level.
 Thus, the two vireo-pairings on these islands showed closer ecolog-
ical niche characteristics than the other closely related resident avifauna,
and should certainly be subjected to a more detailed scrutiny.
 WOOD WARBLERS (PARULIDAE).-The two resident warblers (Den-
droica petechia and D. vitellina) were initially believed to be habitat
restricted, with D. petechia being a mangrove swamp species and D.
vitellina occurring principally in thickets, shrubland, and early logwood
forests. Further observations showed that habitat separation was not
complete because D. petechia is now known to be more widespread,
occurring as a breeding bird in six of the upland ecological formations
(Tables 3-10). On the other hand, D. vitellina is found in only four of


Vol. 19, No. 5