The power requirements (Glossophaginae: Phyllostomidae) in nectar-feeding bats for clinging to flowers

Nectar-feeding bats are the heaviest pollinators exploiting flowers in a hovering foraging mode. As hovering flight is considered to be energetically costly, clinging to flowers would be beneficial from an energetic perspective. I examined the rate of oxygen consumption and carbon dioxide release during clinging flower visitation in two 10-g Glossophaga soricina (Glossophinae: Phyllostomidae) to evaluate the potential energetic benefit of clinging versus hovering. In addition, I measured the duration of flower visits of free-ranging glossophagine bats to Markea neurantha (Solanaceae), a bat-pollinated plant that allows both hovering and clinging flower visitation. After 20 s of clinging to an artificial respiratory mask, the bats' respiratory exchange ratio did not significantly deviate from 1, indicating the combustion of sugar. The average oxygen uptake rate equaled 1.39 ml min(-1) (+/-0.38 SD, STPD) and the carbon dioxide release rate equaled 1.33 ml min(-1) (+/-0.20 SD, STPD) for feeder visits longer than 20 s (n = 79). Converting the oxygen uptake rate into power input yielded 0.49 W, less than a third of the power requirements for hovering for a 10-g bat. Free-ranging 10-g glossophagine bats exploited flowers of M. neurantha for, on average, 0.32 s (+/-0.14 SD, n = 273) during hovering and for 0.39 s (+/-0.18 SD, n = 152) during clinging visitations. A comparison between the power requirements of flower exploitation in differently sized bats indicates that clinging would benefit larger nectar-feeding bats to a greater extent than smaller species.