For bats, a good sense of smell is invaluable.
01.23.25
By Alyson Brokaw
Spicy oranges. Corn tortilla chips. Mint menthols. A touch of bitter almond. What do all these fragrance notes have in common? They can all be used to describe the unique aromas of bats! While bats are known for their keen sense of hearing, having a good sense of smell is also useful for these nocturnal animals for detecting and discriminating food. Smells also play an important role in facilitating social interactions.
Having a sense of smell is an evolutionarily ancient trait – nearly all vertebrates have the ability to sense at least some odors either in the air or in the water. Inside the nose of mammals is a layer called the olfactory epithelium. When odor molecules enter the nose, they bind to special nerve cells called olfactory receptors, which trigger a cascade of electrical signals that travel to the brain. Different odors bind to different olfactory receptors, allowing animals to distinguish between different types of smells – like the difference between a nice ripe fig or a rotten, fermented one.
Smell Evolution
For frugivorous bats hunting for ripe fruit among the leaves or a hungry nectar-feeding bat searching for an open flower after a long night’s journey, a good sense of smell is invaluable. In many cases, bats, their sense of smell, and the plants they feed on have co-evolved. In Central and South America, many of the flowers pollinated by bats have a distinct, musky aroma with an odor profile dominated by a molecule called dimethyl disulfide. Sulfur-containing odors are highly volatile, meaning they evaporate easily and so can be detected from the air. New World nectar feeding bats like the Pallas’s long-tongued bat (Glossophaga soricina) are innately attracted to this smell. In addition to other floral traits, like bright white colors and shapes easily detected by echolocation, the right smell helps flowers attract their pollinators.
Smell helps bats distinguish ripe fruits among dense leaves and foliage. Bats can’t distinguish many colors so looking for a color change to discriminate ripe from unripe fruit is tricky (and many bat-dispersed plants don’t change color when ripe anyway). Instead, bats are good at using smell for this – even when researchers mashed up ripe and unripe fruits into unrecognizable shapes, bats were able to successfully distinguish between them. Cluttered environments, like the dense branches of a fig tree can also make it more challenging for bats to use echolocation to resolve shapes. Odors may help bats cue in on potential food, especially when other senses are less reliable.
In many cases, bats, their sense of smell, and the plants they feed on have co-evolved.
What is that Smell?
Male greater sac-winged bats (Saccopteryx bilineata) take a DIY approach to perfume blending by mixing urine, saliva, and genital secretions together each day and storing the mixture in small sacs located at their elbows. During courtship, males hover and fan their wings towards females to disperse these scents, which have been described as slightly sweet, with a touch of bitter almond. Each perfume blend is unique to the male producing it, and females use these scents to avoid mating with the wrong species or close relatives. Sac-winged bats aren’t the only ones thought to use scents for mating or territoriality. Male fringe-lipped bats (Trachops cirrhosus) in Panama curate a smelly orange crust on their forearms (which smells faintly minty), while male yellow-shouldered bats (Genus: Sturnira) have patches of dark orange-red hair on their shoulder that give off a spicy, orange blossom scent.
Smells play an important role in facilitating social interactions.
Free-tailed bats have a reputation for being particularly smelly. Males of several species develop scent glands under their chins during mating, which they use to scent mark roost spots and females. The specific scents from different species vary – mastiff bats (Molossus rufus) have been described as having a “flowery” scent, while Mexican free-tailed bats (Tadarida brasiliensis) smell more like a bag of corn chips. Scent also plays a role in maternal care in free-tailed bats. When trying to locate their pups in dense maternity colonies, Mexican free-tailed bat females rely on a combination of vocal and olfactory cues. By recognizing the smell of their own pups, females can make sure they are feeding their own offspring and not giving away a free meal to a stranger.
Odors may help bats cue in on potential food, especially when other senses are less reliable.
Odor cues may be used by bats to recognize roostmates, which can be useful for species that frequently change roosts. Big brown bats (Eptesicus fuscus) and Bechstein’s bats (Myotis bechsteini) have shown preferences for the odors of known roost mates over strangers. Female fishing bats (Noctilio leporinus) form small, stable social groups, and will even forage together. They also produce oily secretions from their subaxillary region (aka their armpits) and will mark each other by rubbing their heads against their roost mate’s armpits. I suppose that’s one way to keep track of your friends!
For when its too dark to see clearly, or when sound can’t help, smell is a sensible sense for bats to respond to the world around them!
