A radio-tracking experiment of P. poliocephalus demonstrated substantial movement by bats between colonies several hundreds of km apart (Spencer et al., 1991). Bats typically foraged 17 km from camps and flew directly to feeding grounds, arriving 1 h after departure. The maximum observed foraging distance was 25 km. Individual bats tend to visit the same feeding trees over an extended period (e.g. for 29 consecutive nights). P. vampyrus is known to travel 50 km nightly from roosts to forage, though their movements have not been studied in detail (Mohd-Azlan et al., 2001). E. spelaea can travel 38 km. Pteropus spp. undertake seasonal migrations in areas with distinct wet and dry seasons and adopt non-seasonal “nomadism” in other areas (Marshall, 1983). P. vampyrus may travel from Karimun and Sumatra, Indonesia, to the southwest coast of peninsular Malaysia (Mohd-Azlan et al., 2001).
Large fruits such as mangoes, papayas and breadfruit tend to be consumed in the tree, but most others are carried away to feeding roosts (Marshall, 1983). Larger bats can carry fruit longer distances than smaller bats, though larger bats are more apt to consume fruit directly on trees (Utzurrum, 1995). P. vampyrus (1.2 kg) carries fruits up to 200 g and C. brachyotis (35 g) up to 75 g. Thus, P. vampyrus can potentially disperse fruit several km away from its foraging area, while C. brachyotis usually drops frass within 200 m (Mohd-Azlan et al., 2001). Tan et al. (1997) report food remains beneath the roosts of C. brachyotis on three university campuses. P. conspicillatus forages in small groups and drops frass directly beneath the trees they feed on. Individual “raiders,” however, often steal fruit and carry it away. Larger fruits like mangoes are still dropped within 100 m of their origin (Richards, 1990). Of C. brachyotis, Tan et al. (1998) wrote, “It was quite common for some fruits to be dropped undamaged under the feeding roosts or day-time roosts. In the Bangi Forest Reserve, uneaten fruits with bat tooth marks were often observed on the forest floor.” Some phyllostomids commonly drop 25% of each fruit. They defecate at approximately the same rate as they assimilate food (Bonaccorso and Gush, 1987).
Mohd-Azlan et al. (2001) suggest that the presence of P. vampyrus in orchards reflects food shortages in forests. Hunters and vendors in peninsular Malaysia describe a “bat season” coincident with local fruiting peaks and the arrival of many pregnant bats and bats carrying newborns (Liat, 1970; Fujita, 1988). In Australia, heaviest attacks on cultivated fruit occur following mass blossoming failures of Eucalyptus spp., e.g. after a very wet winter, which suppresses blossoming and washes away nectar. Blossoming can also be suppressed by drought (Richards, 1995). Sometimes unripe fruit is consumed, and attacks are heaviest when females are lactating and particularly nitrogen deficient (Fleming and Robinson, 1987; Tidemann, 1987). They are forced to overconsume carbohydrates to meet their protein requirements (Thomas, 1984); they may also turn to pollen for protein (Tan et al., 1998). One study on the phyllostomid, Carollia perspicillata, estimated that lactating females require 1.5-2 times as much energy as non-breeding individuals, but lactating females had no significant differences in food preferences. Attacks by P. poliocephalus are also dependent on camps’ proximity to farms (Fleming and Robinson, 1987).
General flowering among dipterocarps in the Malay Peninsula occurs every 2-10 years. A general flowering event occurred in Malaysia and Borneo during the early spring of 1996 after a seven-year interval (Yasuda et al., 1999; Kimura et al., 2001). Yasuda et al. (1999) found that flowering among dipterocarps is preceded for two months by a period of low night-time temperatures, usually in January or February. Low night-time temperatures were induced by radiative cooling during winter dry spells, which often occur during La Niña—but never during El Niño—episodes, and are associated with cloudlessness. The intensity of fruit shedding, which follows flowering by 7-8 months, was correlated with the magnitude and duration of the drop in night-time temperature. Another study on supra-annual masting events found that the influence of ENSO on masting was much stronger in eastern peninsular Malaysia than in western peninsular Malaysia, due largely to the mechanism proposed by Yasuda et al. (1999). In winter, local Hadley cell circulation pushes the northern suptropical ridge southward with a dry air mass into the equatorial region, and La Niña episodes intensify this effect. The mountain range running down peninsular Malaysia buffers the western side.
Kimura et al. (2001) note a fruitless period in Borneo in February-April 1997 following the fruiting peak in October-November 1996. A long and severe El Niño event occurred from May 1997 to May 1998 (Wich and van Schaik, 2000). Rainfall in northern Sumatra was 93% of normal; South Sumatra, 56%; East Borneo, 71%; and West Borneo, 61%. The drought was accompanied by forest fires in Borneo and southeastern Sumatra from August-October 1997. Chua (2002) posits that the combined haze and drought led to widespread fruiting and flowering failure. He presents anecdotal evidence of orchard failure in Malacca and Johore, and a 10% decline in rice yields that extended to Trengannu in northeastern peninsular Malaysia (approximately the same latitude as Perak). Oil palm production also fell dramatically in Malacca.
Author: S. Cobey.