Foraging Behavior of Malaysian Nectar-Feeding Bats

Abstract

Feeding strategies of Malaysian nectarivorous bats include trap-line foraging and territorial defense of resources. A high initial-visit rate with a subsequent leveling off of activity by bat pollinators is related to nectar parceling mechanisms of Oroxylum indicum (Bignoniaceae) flowers. Differing temporal patterns of visitation to Durio, Parkia, and Musa reflect different flowering strategies. Patterns of visitation to flowers may provide a useful comparative measure of bat pollination energetics in the New and Old World tropics. PHENOLOGIES TYPICAL OF TROPICAL FOREST include mass flowering of trees over a period of a few weeks and sparse steady state flowering over a period of several months. These two flowering patterns present strategically opposite resources to nectar feeders, i.e., vs. trap-line foraging, respectively (Janzen 1971). Mass flowering and steady state flowering have been subdivided in relation to several species of Central American Bignoniaceae (Gentry 1974). On the basis of his observations in Ghana, Baker (1972) suggests that pteropids usually employ the opportunistic pattern of flower visitation, and that phyllostomatids employ trap-lining. In Ghana, the climatic contrast between clearly defined wet and dry seasons promotes migratory flocks of bats that follow local flowerings. In Malaysia, where the climate remains virtually unchanged the year around, more sedentary bat populations occur. Observations presented below indicate that and trap-lining strategies have evolved in the Old World as well as the New World. A nectar parceling mechanism in the flowers of Oroxylum indicum can be related to the temporal pattern of bat visitation. Other plants which present flowering patterns strategically opposite to Oroxylum evoke different visitation schedules and, in one case, territoriality. In Malaysia, Start ( 1974) and Start and Marshall (1975) have demonstrated that pollen from mass flowering and steady state flowering species of plants occur in the guano of Eonycteris spelaea, Megachiroptera, in Batu Cave. The combination of pollen representing both flowering strategies implies that Eonycteris use at least two different feeding strategies. Previous studies suggest that most bat flowers accommodate many species of bats; Oroxylum may be an exception. The occurrence of pollen of Oroxylum indicum (Bignoniaceae), a steady state flowering form in the guano, and my knowledge of some floral features of Oroxylum led to the investigation of the degree of specialization with which plant structures are associated with anatomical and behavioral traits of Eonycteris. THE BAT.-There are three species of truly nectarivorous bats in lowland Malaysia, Macroglossus minimus, M. sobrinus, and Eonycteris spelaea, which have little ecological overlap (Start and Marshall 1975). Both Macroglossus species roost alone or in small groups in trees and specialize on Musa and Sonneratia. Two other common species, Pteropus vampyrus and Cynopterus sphinx, feed on fruit and nectar. Eonycteris is a fast-flying, nectar-feeding bat weighing 50-80 grams, which roosts in large colonies on the high ceilings of sparsely distributed caves in Malaysia (Lim 1966, Start 1974, McClure et al. 1967, Medway 1959) in tower karst scenery (Gabbett 1965, Rajah 1970). Based on Soneratia pollen in the guano and on the nearest source of Soinneratia, Start (1974) estimated that many Eonycteris forage more than 38 km from the cave. Typical of the family Pteropidae, Eonycteris has large eyes and does not echolocate (Novick 1958). THE PLANT.-There are at least 31 species of chiropterophilous plants in Malaysia. Many are massflowering species (Durio, Ceiba, and Parkia), but a few species flower in steady state for most of the year (Musa and Oroxylum) or in flushes once or twice a year (Sonneratia) (Start 1974). Oroxylzm is a semi-deciduous tree, up to 26 m tall (fig. 1), with a companulate and bisexual flower. As is typical of the family, the filament bases are densely lined with a collar of hairs (fig. 2). There are 130-226 flower buds arranged axially on a 1 to 2 m flagelliflorous inflorescence. One to four flowers open each night. A tree may produce one to 40 simultaneously flowering inflorescences (x 7.5 inflorescences, Sd 5.2, n 29 trees), which yield 184 BIOTROPICA 10(3): 184-193 1978 This content downloaded from 157.55.39.27 on Wed, 07 Sep 2016 04:37:51 UTC All use subject to http://about.jstor.org/terms an average of 4.3 pods/inflorescence (Sd 2.6; range 1-12 pods on 190 inflorescences of 57 trees). A pod contains ca 230-325 seeds (n=7 pods on 3 trees). Eonycteris occurs throughout the distribution of Oroxylum except India and Ceylon, where it is replaced by Cynopterus sphinx. The coincident distribution of bat and plant includes Thailand, Cambodia, Malaysia, Borneo, Indonesia, the Philippines and the Celebes (Steenis 1927, Walker 1974).