BONACCORSO: A PANAMANIAN BAT COMMUNITY


and whipscorpions. Janzen (1973) and Janzen and Schoener (1969)
reported that watersheds are dry season refugia for many insect
groups in tropical forests. Perhaps some individuals or populations of
gleaning carnivores move to riparian habitats off the island during
lean times.
 Micronycteris, Tonatia, and Trachops bear two litters per year. The
first pregnancy of the year for these species occurs during relative food
scarcity, but the birth pulse occurs as large insects are becoming abun-
dant. The first lactation and the entire second reproductive cycle occur
within months of food abundance.
 The peak in pregnancy for Mimon crenulatum, a monestrous
species, occurs about two months after those of the above gleaning car-
nivores. Thus both pregnancy and lactation occur within the year's
peak of insect abundance. Mimon can time its reproductive activity in
this manner because it does not squeeze two reproductive cycles
within the months of large insect abundance as do the polyestrous
species of the guild.
SLOW-FLYING HAWKING INSECTIVORES
 Much less is understood about resource partitioning, foraging
 strategy, and reproductive strategy within this guild than in the
 guilds discussed above. It is possible that each family placed in this
 guild should constitute a distinct guild, but not enough is known to be
 certain. A common denominator among all these species is that they
 capture small aerial insects and eat them while flying. Some guild
 members have individual or group feeding territories. Territorial
 defense of foraging areas may serve as the primary means of decreas-
 ing intraspacific interference over food. Body size, microhabitat, and
 activity cycle differences are likely possibilities as primary
 mechanisms that reduce interspecific competition for food within the
 hawking insectivores.
 Small insects are abundant all year long, although specific insects
 fluctuate in abundance (Smythe 1974). These bats do not undergo
 shifts in diet type as many other species are forced to do. Foraging ac-
 tivity occurs in bimodal periods on nocturnal or crepuscular regimes.
 Hundreds of very small food items must be eaten each night requiring
 very high capture and feeding rates (Gould 1955) compared to other
 bat guilds.


1979