BONACCORSO: A PANAMANIAN BAT COMMUNITY


night (especially true of pipers) and a given shrub may be stripped of
fruits by other bats before an individual visits it or between return
trips from the feeding roost. When suitable canopy species are fruiting
they are included in the diet. Fruits are picked from the resource plant
and carried to feeding roosts for eating. Most fruits eaten by these
bats are mature only from one to three consecutive months; thus
groundstory frugivores must frequently change food species and
search images. Some insects are eaten, but it is not clear whether these
are taken with fruits or independently hunted.
 The reproductive strategy of the groundstory frugivores on BCI is
similar to that of canopy frugivores.

NECTAR-POLLEN-FRUIT-INSECT OMNIVORES
 Moist and wet tropical forests have few large flowers suitable for
 bat pollination and feeding, and these are primarily available in the
 dry season (late December through March on BCI). Extreme nectar-
 pollen specialists among the Microchiroptera are common only in dry
 tropical forests and deserts (Humphrey and Bonaccorso 1978). Only
 species like Phyllostomus discolor and Glossophaga soricina that
 switch to other types of food in the wet season make prolonged use of
 dry season flowers in moist forest, though some frugivores occasional-
 ly visit flowers.
 The mechanisms of resource partitioning among nectarivorous
 bats are poorly understood. My data and those of Heithaus et al. (1974)
 and Alvarez and Gonzales (1970) indicate almost complete overlap
 among bat species in the use of flowers. Flowers do have activity
 cycles with respect to nectar production, and it is suggested by
 Heithaus et al. that temporal differences in bat activity serve to parti-
 tion nectar and pollen among bats. On BCI the foraging activity of P.
 discolor is compacted into the twilight and first hours of darkness, pro-
 bably as a response to inter- and intraspecific competition over nectar.
 The first bats that arrive at a flower each night receive a maximal sup-
 ply of nectar and successive visitors receive lesser amounts (Heithaus
 et al. 1974).
 Both Glossophaga and Phyllostomus feed primarily on nectar and
 pollen as long as flowers are available. As the wet season begins,
 Phyllostomus switches to fruit and insects, and Cecropia fruits
 become particularly important. In the dry forests of Costa Rica where
 Cecropia is not a common tree, Phyllostomus disappears after the dry
 season flowering and does not reappear until the next flowering season
 (Heithaus et al. 1974). I expect that they migrate to and from habitats
 that have Cecropia fruits available in the wet season and large flowers
 in the dry season.


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