In the Naruto verse, there were two signers of the bat contract. Rinji and Tonbee.
Rinji had the ability to use ultra sonic sound waves to effectively control the bats to do his biddings. They proved important to counter the crystal release used by Guren. He could also control them to search an area or a perimeter.
Tonbee on the other hand, summoned a bat in the Six tailed unleashed arc that transform into a scroll.
IN REAL LIFE.
Bats are mammals of the order Chiroptera (/kaɪˈrɒptərə/ ; from the Ancient Greek: χείρ - cheir , "hand" and Ancient Greek: 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 , can only glide for short distances. 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 are the second largest order of mammals (after the rodents ), representing about 20% of all classified mammal
species worldwide, with about 1,240 bat species divided into two suborders: the less specialized and largely fruit-eating
megabats , or flying foxes, and the highly specialized and
echolocating microbats. About 70% of bat species 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
hemato****ous, or feeding on blood.