Relative role of olfactory cues and certain non-olfactory factors in foraging of fruit-eating bats.

The proportion of captivated Indian short-nosed fruit bats, Cynopterus sphinx, approaching fruits within a specified duration and the fruit-approaching latency were recorded under various test conditions (involving variations in the olfactory and certain aspects of the physical environment, and the time of food presentation). While alterations in the majority of physical features in the immediate environment of bats failed to affect either of the foraging parameters studied, one or both of them were markedly influenced by the presence of light or source of a novel odour, or a delay of 24 h in the regular feeding time. When paper pieces coated with homogenized fruit pulp were provided instead of the fruit pieces during the regular feeding time, bats responded normally; they, however, did not approach water-wetted papers. Initially the bats did not consume grapes. However, following the supply of grapes coated with homogenate of banana fruits, grapes were approached and consumed in considerable quantities. The results underscore that light has a crucial role in the foraging activity of C. sphinx and they rely extensively on olfactory cues to detect the fruits. In another experiment the bats were daily provided simultaneous access to two adjacent fruit-containing cages; fruits in one of the cages were accessible but those in the other cage were not. Cedar wood oil, source of a strong odour, was placed in either of the cages. Observations revealed that the bats can learn to associate the availability of fruits with the presence of an odour within 3 days.