A Tiny Bat That Can Fit In Your Palm - BBC Travel

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In 2015, severe flooding wiped out La Isla. Though, by the look of it now, I wouldn't have known. Enormous cecropia and balsa trees had already grown taller than the bridge, and dense vegetation obscured the island floor. The tiny bats, however, haven't yet returned. Scientists speculate that the understory is too crowded with new growth, making it hard for them to easily leave their tents.

But we were lucky that day. Inside the reserve, just a few hundred meters after the bridge, Rojas Valerio pointed out fraying empty tents along our trail, then led me into marshy woods with mud up to our ankles. In the middle was a neatly folded leaf with a brown ridge on top. Underneath, the bats looked like a handful of fuzzy green seeds, a surprisingly effective form of camouflage. When Rojas Valerio turned on his torch, they transformed into white cotton balls with yellow-orange noses and ears. A shiver ran through the upside-down colony of five females, one male and a baby. One opened its eyes and stared at us, dewy black slits embedded in snowy fur.

It was impossible not to coo. One of the smallest fruit-eating bats in the world, the tent-making bat has an average wingspan of just 10cm and weighs roughly 6g – about a teaspoon-and-a-half of sugar. According to Bernal Rodriguez, bat biologist and professor at the University of Costa Rica, these diminutive creatures are the only known mammals with an accumulation of carotenoid pigment, the chemical that accounts for the bright yellow of their ears and nose. The carotenoid comes from peels of the bats' food: cranberry-like figs from a particular tree, Ficus columbrinae, that grow near rivers. Recent studies by Rodriguez and his team suggest that the colouring is a trait of sexual selection. Males that are larger and well fed have brighter colours, a feature that attracts females.

Emmanuel Rojas Valerio