Hovering flight is metabolically expensive, and a nectar-feeding bat hovers repeatedly through a night at hundreds of flowers. Glossophaga soricina sustains one of the highest mass-specific metabolic rates recorded in a mammal.
Stable-isotope work by Kenneth Welch, Christopher Voigt and colleagues traced the carbon in exhaled breath after a labelled sugar meal. Within minutes, a large share of the carbon dioxide the bat exhaled during hovering came from the sugar it had just drunk, meaning ingested nectar was fuelling flight muscle almost directly rather than being converted to stored fat and drawn on later. Hummingbirds do the same, which makes this a convergence between a bird and a mammal under identical energetic pressure.
The pollination consequence is that the bat must visit a great many flowers each night, and neotropical bat-pollinated plants are correspondingly built for repeat visits: sturdy nocturnal flowers with dilute, copious nectar. What remains debated is how flexibly the bat switches between drinking sugar and drawing on fat as nectar availability changes through the night.