BULLETIN FLORIDA STATE MUSEUM


the two groups, corporately and individually, partition food resources?
To what extent is behavior (territoriality, if it exists, and aggression)
important in these syntopic relationships?
 In the first place, the augmentation of a rather depauperate resident
 population in the mangrove swamps by wintering migrants strongly
 suggests two things: (1) during the breeding season there are probably
 unoccupied feeding niches or limited food resources in mangrove swamps,
 assuming that (2) a reasonably constant annual food supply is available.
 No data have been assembled on food resources; however, it may be
 noted, by way of example, that in mangrove swamps foliage-gleaning
 insectivores are represented in summer by one resident (Dendroica
 petechia), whereas in winter D. caerulescens, Parula americana, Seto-
 phaga ruticilla, and others also occur. (Multispecific warbler flocks in
 winter are well known from other Caribbean islands, such as Puerto Rico
 [see Recher 1970: E-78].) This winter increase of the avifauna at a
 single trophic level strongly suggests an abundant insect food supply dur-
 ing that season. Furthermore, in the mangrove swamps a number of
 feeding niches are filled only in winter-trunk and branch-gleaning for
 small insects (by Mniotilta varia), aerial-feeding small insectivores
 (Setophaga ruticilla, Polioptila caerulea), ground-feeding insectivores
 (Seiurus noveboracensis and S. aurocapillus). Possibly insects are less
 abundant in these swamps in summer than in winter, but I suspect there
 is a high annual insect population that is simply underexploited by the
 resident birds in summer. In other words, some feeding niches are un-
 filled during the summer. Similar arguments might be made, inciden-
 tally, for the other ecological formations.
 Competition for food, at least in the form of overt aggressive pur-
suits, does not appear to be very evident between the residents and mi-
grants. The reason for this is at least partially explained by the fact that
feeding ecologies of residents and migrants are generally dissimilar. The
resident insular birds such as doves, woodpeckers, cuckoos, the parrot,
flycatchers, and the bananaquit, have virtually no competitors among the
wintering migrant birds. When active pursuits were observed, they were
infrequent, of short durations, and appeared to involve intraspecific ac-
tions among the residents (such as two Dendroica petechia) or interspe-
cific and intraspecific actions among the migrant warblers or other species.
(Chases were often so rapid that neither bird could be positively identi-
fied.) Also central, localized feeding (fruiting) trees so characteristic of
other tropical forests are apparently not an important ecological com-
ponent in any of the Cayman Island formations; hence, competition at
such a localized site is virtually nonexistent.
 In summary, it appears that the large number of wintering birds in-


Vol. 19, No. 5