Mammals
Honduran White Bat
Ectophylla alba · also called Caribbean white tent-making bat
Look closely at the underside of a drooping Heliconia leaf in a Costa Rican rainforest and you may find a row of white puffballs the size of cotton buds. They are Honduran white bats, one of the very few white bats in the world, sheltering in a tent they cut for themselves out of the leaf.
Overview
Ectophylla alba is a tiny fruit bat, about 4 cm long and 5 to 6 grams, with pure white fur and bright yellow-orange ears, nose-leaf, and wing bones. It lives only in the Caribbean lowland rainforest of Honduras, Nicaragua, Costa Rica, and western Panama, below about 700 m, and it feeds almost entirely on the fruit of one fig species, Ficus colubrinae.
The tent
Small groups of these bats build leaf tents. They chew through the side veins of a large leaf so the halves fold down into an inverted V, then roost in a cluster clinging to the midrib underneath, sheltered from rain, sun, and predators. Sunlight through the green leaf casts a greenish light, and the white fur picks up that tint, so from below the huddled bats blend into the leaf instead of showing as pale spots.
Colour from figs
The bat’s vivid yellow skin comes from carotenoid pigments in its fig diet, deposited in the bare skin of the face and wings. A 2016 study identified it as the first mammal known to colour its skin this way — a trick otherwise seen in birds, fish, and reptiles.
Status
The Honduran white bat is Near Threatened and declining. It depends on both its single fig species and a steady supply of suitable large leaves in the forest understorey, so it cannot survive where Caribbean-slope rainforest is cleared for farms and pasture.
Honduran White Bat: common questions
Why is the Honduran white bat white?
Very few bats are white, and this species is one of the most strikingly so, with pure white fur over the whole body. The leading explanation is camouflage in its unusual roost. The bats shelter under living green leaves, and sunlight filtering through the leaf bathes the space beneath in green light. White fur under green light looks greenish, so the huddled bats blend into the underside of the leaf when seen from below by a predator such as a snake or a bird. A dark bat would stand out as a shadow; a white one nearly disappears.
How does the Honduran white bat make a tent?
A group of bats works along a large leaf, usually a Heliconia, and bites through the side veins that run out from the central midrib. Cut in the right places, the leaf loses its rigidity and the two halves fold downward into an upside-down V or a tent shape. The bats then roost in a tight cluster clinging to the midrib on the underside, protected from rain, direct sun, and the eyes of predators. A tent lasts a few weeks until the leaf dies or droops too far, and the group builds or moves to another nearby.
What do Honduran white bats eat?
They are fruit specialists, and unusually narrow ones. Studies in Costa Rica have found that their diet is overwhelmingly the fruit of a single fig species, Ficus colubrinae, which they locate by smell and visit when it is producing ripe figs. Other small figs are eaten rarely. This tight link to one plant is part of why the bat has such a limited distribution and why it is considered vulnerable to habitat change, since losing that fig from an area of forest effectively removes the bat's food supply.
Why do the bat's ears and nose look yellow?
The bare skin of the nose-leaf, ears, and the bones visible through the wing membranes is a vivid yellow-orange, and this comes from carotenoids, the same class of pigments that make carrots and egg yolks orange. The bat takes them in from its fig diet and deposits them in the skin. A 2016 study identified this as the first known case of a mammal accumulating pure carotenoid pigment in the skin to produce visible colour, a trick otherwise associated with birds, fish, and reptiles. The function is not certain but may relate to mate choice or to the skin itself.