Bats

Bats are mammals of the order Chiroptera  /kaɪˈrɒptərə/; from the Greek χείρ - cheir, "hand"and πτερόν - pteron, "wing) whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly, and can only glide for a short distance. Bats do not flap their entire forelimbs, as birds do, but instead flap their spread-out digits,which are very long and covered with a thin membrane or patagium.
Bats represent about twenty percent of all classified mammal species worldwide, with about 1,240 bat species divided into two suborders: the less specialized and largely fruit-eating megachiroptera, or flying foxes, and the more highly specialized and echolocating microchiroptera^. About seventy percent of bats are insectivores. Most of the rest are frugivores, or fruit eaters. A few species such as the Fish-eating Bat feed from animals other than insects, with the vampire bats being the only parasitic mammalian species. Bats are present throughout most of the world, performing vital ecological roles of pollinating flowers and dispersing fruit seeds. Many tropical plant species depend entirely on bats for the distribution of their seeds. Bats are important in eating insect pests, reducing the need for pesticides. The smallest bat is the Kitti's Hog-nosed Bat, measuring 29–34 mm (1.14–1.34 in) in length, 15 cm (5.91 in) across the wings and 2–2.6 g (0.07–0.09 oz) in mass. It is also arguably the smallest extant species of mammal, with the Etruscan shrew being the other contender.^{[citation needed]} The largest species of bat is the Giant Golden-crowned Flying Fox, which is 336–343 mm (13.23–13.50 in) long, has a wingspan of 1.5 m (4 ft 11 in) and weighs approximately 1.1–1.2 kg (2–3 lb).

Classification and evolution

Giant Golden-crowned Flying Fox, Acerodon jubatus.

Bats are mammals. They are often mistakenly called "flying rodents" or "flying rats". In many languages, the word for "bat" is cognate with the word for "mouse": for example, 'chauve-souris' ("bald-mouse") in French, 'murciélago' ("blind mouse") in Spanish, 'летучая мышь' ("flying mouse") in Russian, 'nahkhiir' ("leather mouse") in Estonian. An older English name for bats is flittermice (singular flittermouse), which matches their name in other Germanic languages (for example German Fledermaus and Swedish fladdermus).They can also be mistaken for birds. However, they are not directly related to rodents, and much less to birds, and do not in fact have any closely related orders (their uniqueness can be demonstrated by the fact their closest living genetic relatives are thought to be carnivorans, certain hoofed animals such as alpacas and hippopotamuses, and sea mammals such as dolphins.)

How Does Rain Mess With Bat Flight—Thermodynamics or Aerodynamics?

What’s the News: Bats have to use twice as much energy to fly when they’re wet as when they’re dry, a new study in Biology Letters found, which may help explain why many bats refrain from flying in heavy rain.
How the Heck:

• The researchers captured ten Sowell’s short-tailed bats in Costa Rica.
• Each of the bats flew around a large outdoor cage in three different circumstances: dry, wet (the researchers dampened their fur and wings with tap water) on an otherwise dry day, and wet on a fairly rainy day.
• By measuring the bat’s metabolism, the researchers found that wet bats expended twice as much energy during a short flight as dry bats did (twenty and ten times their resting rate, respectively).
• The wet bats didn’t weigh more than the dry ones, ruling out the idea that the damp bats simply had to work harder to carry extra water weight. Nor did already wet bats burn more energy flying on a rainy day than a dry one, meaning the problem isn’t that raindrops mess with the bats’ flight mechanics.
• The researchers suggest two other explanations: Being wet might cool the bats down (the same way sweat cools humans down), meaning that they have to boost their metabolisms to stay warm. Or, wet fur might make the bats less aerodynamic, meaning it takes more power to fly.

What’s the Context:

• Another theory about why bats tend not to fly in the rain posits that rain gets in the way of echolocation, the means by which bats find their food. This study doesn’t disprove that theory; bats could have more than one reason for staying out of the rain.
• Of animal groups that fly, only bats are furry; birds, for instance, have feathers to protect them from the rain.