JOHNSTON: CAYMAN ISLAND AVIFAUNA


these columbids partition resources so as to permit (1) sympatry on the
island and (2) syntopy in given ecological formations? It is initially
important to admit the paucity of information on their breeding habits,
seasonality of breeding (see Table 13), and feeding behavior. Never-
theless, from the available information summarized in Table 15, it ap-
pears that the columbid species partition resources in two principal
fashions-by habitat selection and by food type. As breeding birds, no
more than three species are found in a given ecological formation (Tables
3-10). All these species are basically frugivorous and, for the syntopic
species, limited stomach analyses (see Appendix III) do not indicate
any marked interspecific differences in food habits.

TABLE 15.-NICHE CHARACTERISTICS OF DOVES AND PIGEONS ON GRAND CAYMAN.

1 Leptotila jamaicensis 1
 BS
2 Columba leucocephala FH 2

 (H),BL BS,BL
3 Zenaida aurita FT FH,FT

 4 ..BL,H (BS) BL,(BS)
4 Zenaida asiatica FT? FT? FT?

 BS,BL BS,BL BS,BL BS,BL
5 Columbina passerina H, FT H,FH FT (H),FH
 FT FT

Key: BS (body size), BL (bill length), H (habitat), FH (feeding height), FT
 (food type). A symbol in parentheses indicates that the difference is poorly
 developed.

 WOODPECKERS (PICIDAE).-The two resident woodpeckers (Colaptes
auratus and Centurus superciliaris) of Grand Cayman were earlier be-
lieved to be ecologically separated, chiefly on the basis of habitat, with
Colaptes supposedly being a bird of the mangrove swamps and Centurus
most common around human habitations (Johnston 1970). Subsequent
intensified study by Alex Cruz and me showed, however, that these species
were not necessarily separated by habitat differences. As seen earlier
in the distribution analyses of birds in the various ecological formations
(Tables 3-10), clearly both woodpeckers occur together in most of these
wooded formations, although Colaptes predominates in mangrove
swamps. Overall, the differences in habitat choice between these two
woodpeckers are only of minor importance (Table 16).
 The principal niche differences between these species are in feeding
methods and food type. Colaptes is essentially a probing and drilling


1975