Bat Pups

07.03.24

By Paul Hormick

Back in February, we blogged about bat sex and the ways bats go about their “lovemaking.” Well, bat sex leads to bat offspring, so today we look at bat moms, bat babies, and even put in a word for the bat dads.

Most smaller animals have shorter gestation periods. Bats buck this trend, having fairly long pregnancies. While insectivorous bats in temperate climates gestate for around three months, tropical fruit bats may take as long as five months to go from conception to birth. Vampire bats are pregnant almost as long as humans, seven months. Comparatively, bat babies are really big. For some species, newborns can weigh 43 percent of the mother’s bodyweight.

Most bat mothers give birth to a single pup, but some species have multiple births, two, three, even four offspring. Twins are common in some species. As raising twins means twice the nursing and care as raising a single pup, expectant mothers of the common noctule, a bat found in Europe, Asia, and North Africa, can assess their success of raising twins, using their bodyweight as a guide. These expectant mothers then have the remarkable ability to choose whether or not to give birth to twins or a single pup.

Roosting as usual, mama bats give birth upside-down, licking and grooming their pups as they emerge from the birth canal, and protecting them with their wings. Born hairless and with their eyes closed, bat infants then crawl to their mother’s nipples, attach themselves, and feed.

In many bat species, females gather in large colonies to give birth. Those who study bats believe group nurseries keep the pups warm and enable bats to ward off predators. Giving birth in groups may help in other ways, as there is at least one observation of a bat helping another bat give birth. In this instance, the “midwife” bat groomed the newborn and helped it find the mother’s nipple. For species that live in smaller groups, bat fathers also care for their young.

In their large maternal colonies, Mexican free-tailed bats sometimes inadvertently serve as wet-nurses for each other. Although mothers recognize their babies by the sounds they produce and their scents, a little more than 15 percent of the time they will nurse the pups of other bats. It seems the babies can get quite aggressive when it comes time to nurse, and if mom is not around, another mommy bat will do just fine.

In the initial stages of infancy, babies ride along with their mothers while they hunt or forage for food. During flight, bat babies hold on with everything they’ve got, sharp claws, even their teeth. Once pups start roosting on their own, mothers fly off to feed but may return several times during the night to nurse or feed.

Looking at the greater sac-winged bat, a species native to Central and South America that has a larger vocal repertoire, researchers discovered baby bats babble as they learn to communicate, uttering the bat equivalence of the goo-goos and ga-gas we hear coming from a baby’s crib. And as far as we now know, bats are the only other mammal to share this quality with humans. Even more surprising, baby bat vocalizing has the same eight characteristics, such as repetition and rhythm, as human baby babbling.

            Bat parents are also similar to human parents in this regard. Just as we pick up a slower, exaggerated, sing-songy, manner when we talk to infants and toddlers, bat mothers speak a similar “motherese,” changing the timbre and pitch of their vocalizations when they “talk” to junior. And as they learn bat communication, pups pick up the local bat dialects of their parents.

Imagine learning your surroundings and how to get around while flying upside down and in the dark. But that is exactly how mothers carry their young and how bat pups learn to navigate. Scientists used GPS tracking of both mothers and offspring to see how youngsters developed the ability to forage on their own. Mothers repeatedly flew their little ones to the same trees, over and over. Once the pups were able to fly independently, they followed similar routes their mothers had taken and returned to the same sites where their mothers had repeatedly dropped them off. As they grew up, they ventured to additional sites to feed and explore.

Apparently, bats born in and around cities can be more metropolitan than their country- dwelling cousins. Researchers recently found that urban Egyptian fruit bat pups learned about their environment faster than pups raised in rural settings. The city bats were also more likely to take risks than their country cousins.

In most species, pups learn to fly within three to six weeks after birth but remain dependent on mother for four to five months for nursing and feeding. It is then their turn to fly off, mature, mate, and have bat offspring of their own. And at BCI we want to ensure that all bats continue this reproductive cycle, especially the 200 species threatened with extinction.

BONUS CONTENT

Watch baby Mexican free-tailed bats in Bracken Cave July-August.