Scent of solidarity

Short-nosed fruit bats have fancy ways of roosting in group sand use odour to identify their buddies

Baheerathan Murugavel became fascinated by fruit bats during his postgraduate studies in Madurai, Tamil Nadu. Unlike the poor-sighted insectivorous bats which echolocate their way through life, the fruit-eaters navigate long distances and orient themselves to landmarks in the dark by sight. But they also rely on their widely spaced nostrils to catch a whiff of the heady aroma of flowers and ripening fruits. The short-nosed fruit bats take their olfactory perception to an extreme.

Since they roost in groups, they use odour to identify their buddies. Weighing as much as two AA batteries, they are one of only two species to build a nuptial chamber that also serves as a maternity ward and nursery.

Several months ahead of the twice-a-year breeding season, the orange-brown male spends up to eight weeks crafting ‘tents’ in palm fronds, mast trees, and creepers. He gnaws the midrib of leaflets or thin branches that collapse to create a bell-shaped abode. Then he marks his ownership by licking the inner walls as thoroughly as a cat cleaning itself. Some enterprising males construct an extra tent. This is especially crucial if one collapses, leaving little time for repairs. Bachelors that don’t have the foresight to work on a backup shelter sleep alone in their retreats or in building eaves should their refuge be damaged.

Mere possession isn’t enough; the tent needs decoration. He chews the peel of wild citrus fruits and leaves of other trees and smears the fragrant paste on the walls of the enclosed space. He is his own real estate agent, and his customers are exclusively females. To advertise his assets to prospective mates, he rapidly fans his wings to diffuse the scent into the air.

Olive-grey females evaluate partner material through his construction and interior decoration skills. Once they signal their approval, he seals the deal by hugging and smearing them with an oily secretion produced by glands in his wings. As many as 15 females marked by the mouth and body odour of their mate may huddle with him in this shelter during the day.

As sunlight wanes, an early riser starts scratching, licking, and moistening itself. Soon, as if grooming were infectious, the whole bevy becomes a tangle of soft furry bodies and naked skin-covered wings, vigorously anointing each other’s fur. “They drench each other in saliva,” says Murugavel. “And the tent shakes with all that activity.” This intimate primping serves more than one purpose. It helps the members recognise each other by smell, and the group huddle may soothe the frayed nerves between housemates which live in cramped quarters. Perfumed and becalmed, they set off to feed not only on flowers and fruits but also on nectar and leaves. The male doesn’t have the luxury of taking his time over dinner. Leaving a coveted home wide open is not a human concern alone. He quickly feeds within a 500-m radius and returns to his abode, where he spends most of the night safeguarding it from rivals. When his consorts return, guided by the tent’s bouquet, they are welcomed with a smelly hug. Should an unfamiliar female enter, the residents send her packing.

At the end of the season, pups fly the roost, but their parents don’t suffer from the empty nest syndrome. Some females continue to spend their days in the tent, with a few bonding with each other and choosing the refuge of the same male year after year. He continues to guard his structure as long as it is undamaged or unmolested by predators such as crows, owls, and snakes. Such protracted tenancy attracts more females when the next breeding season rolls in.