Bats: Reproduction

Summary: How do bats make more baby bats? Let us count the ways! Join Kiersten as she discusses the various reproductive techniques bats use to make more bats.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean

 

Show Notes:

“Bats in Question: A Smithsonian Answer Book,” by Don E. Wilson

Music written and performed by Katherine Camp

Transcript

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Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

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Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

I apologize for missing last week, listeners. The holidays snuck up on me and I just didn’t have time to write, record, edit, and post before Christmas was upon me. Let’s get back to bats!

The fourth thing I like about bats is making more bats! Chiroptera reproduction is interesting and diverse. Microbats and Megabats are mammals, so they give live birth and nurse their young with milk, but we’re going to take a closer look at the reproductive cycle of some of the specific species of bats in this episode. 

As my loyal listeners know, I earned my Master’s of Science in Animal Behavior by studying the breeding behavior of the Tri-colored Bat, Perimyotis subflavus. I chose to study the breeding behavior of this particular bat because they are heavily impacted by White-nose Syndrome, a disease that impacts the hibernation behaviors of bats that overwinter in caves that remain around 55 degrees or cooler throughout the year. Many of the caves on the East coast of the United States fit this bill. I will be talking more about this problem in a future episode. The reason I wanted to study the breeding behavior is because we did not have a record of how these bats reproduced. If their numbers fell so low that we needed to intervene to help save the species from extinction, it was essential that we knew how they reproduced so we could offer everything they needed in a captive setting.

So, off I went with my husband in tow to sit for hours at a time in a dark cold cave at 2am to record the behavior of hibernating Tri-colored Bats. What did I learn? We discovered that in this cave, the Tri-colored Bat males will seek out females during their hibernation periods and mate with them. Yes, that’s right these little boogers mate with the females while they are sleeping! We were shocked! But it is the optimal time to mate with females without having to expend excessive amounts of time and energy vying for their attention. 

I agree that it sounds terrible. Not very nice at all. No consent from the females, but it works for this species of bat. The males and females go their separate ways as soon as the winter season passes so the males have no chance to breed later in the year. The female’s body stores the sperm until it is needed. When the time is right, the sperm will fertilize the egg and she will become pregnant. 

Many species that hibernate in caves breed during the fall season as males and females are swarming into the caves. For these species there are two paths to fertilization. One I just talked about, where the female stores the sperm in her reproductive tract until spring. Another path is immediate fertilization. Long-fingered bats from the Old World practice this method. The females and males breed in fall and fertilization happens immediately, but development of the fetus is slowed during hibernation so that the female will be ready to give birth come spring. 

For species that have a long distance migration, such at the Brazilian Free-tailed Bat, breeding occurs most often in the early spring as they are entering their summer roosts. The physical stress placed upon them by a migration from Central America to the Southern United States may prevent them from breeding until they reach their destinations.

Tropical species of bats that are not impacted by temperate weather changes have a greater variety of reproductive patterns. Insectivorous species that rely on invertebrates for food are constrained by the wet and dry seasons and typically have one offspring a year during the height of insect season. 

Species of neotropical fruit-eating bats will often have two reproductive cycles a year. Bats in family Phyllostomidae will breed early in the year, a few months later the young are born, then the females will enter a postpartum estrus and become pregnant again. This allows them to have more young during the flowering and fruiting season of the year before the rainy season begins. The Jamaican Fruit Bat has a slight alternation in that they will breed early in the year and birth young a few months later as we just discussed, but their second cycle will have a lengthened fetal development, so that they are pregnant during the rainy season and birth their second young when the dry season occurs again.

Now, attracting mates is something that many species of bats have to concern themselves with, and they have so many ways to do it!

The Gambian Epauletted Fruit Bat has whit tufts of fur on it’s shoulders that are used to attract a female. With this and an attractive scent release by glands, they attract a female for mating. This is an active form of mating where the female chooses her mate. 

African Hammer-headed Fruit Bats form leks during breeding season. Leks are display grounds where males gather to perform to attract and win a mate. These particularly bat males will call loudly to get a female’s attention as she passes and hopefully win her favor. 

Courtship displays can include wing-flapping, vocalizations, and mutual grooming. Sac-winged bat species will hover in front of a female while opening a glandular sac that is located in front of each wing. We presume that he is wafting a pheromone at her to win her attention. 

In some flying fox colonies where males and females roost together throughout the year, males do very little to attract a female’s attention for mating and often mates with her even when she doesn’t appear to agree. 

When young are born, females will give birth in a roost site. Sometimes that is in a nursery, like the Mexican Free-tailed bats, where many mothers are giving birth in the same place. Sometimes that is in a smaller colony with males and female together such as many flying fox species. And sometimes that is alone, like the red bat species of North America, that are solitary roosters. 

Young are born hairless and helpless. Their eyes are closed and they cannot fly. They will drink milk produced by their mother. During birth, some mothers will hang upside down and the young will instinctively grasp onto the mothers fur, while some Megachiroptera will use their thumb-like hooks to hold onto a branch creating a four pointed position that helps them catch their young as they are born. 

There is evidence that fruit bats that live in the same colonies throughout the year will have helpers at birth. Older females will come to the aid of new mothers, physically helping them birth their young and guiding the pup into their arms, while younger females will roost nearby watching. This has been seen in captive colonies many times, with one or two reports from wild colonies. But, boy oh boy, what an amazing behavior! There is still so much we have to learn about bat social behavior.

Young are born feet first so they can help pull themselves out of the birth canal. Bat young typically weigh up to 40 percent of the mother’s own body weight. That’s like a 115 pound woman, or approximately 40 kilos giving birth to a 40 pound baby, or a 20 kilo baby. Holy smokes! 

Bats that roost in large nursery colonies will leave the young behind, gathered tightly together to conserve body heat, when they hunt and return to nurse the young through the daytime. They find their young without fail every time they come back to the colony.

When young are first born, or in solitary nesting species, mothers will keep the babies on them as they search for food. They will cling to the armpit area holding on with the well developed thumb hooks with their mouths latched onto a nipple. Can you imagine flying around at night looking for insects with a baby attached to you that weights almost half your own body weight?!

Most species of bats will birth only a single pup, yes bat babies are called pups, at a time. A handful of species will birth twins, such as the Hoary Bat and the Red Bat, and will have one pup attached to each nipple. Most bats have only two nipples so producing more than that can be problematic. Not to mention how big each baby is!

The bats in the Lasiurus Genus can have two, three, four, or five pups at a time. They have four nipples so larger litters are doable. 

Bat pups grow quickly and are typically flying on their own at about about thirty days or so. Once they can fly, they are on their own. Or so we think. We are still studying this and some research shows that young my rely on their mothers for a longer period of time. They may learn much more from their mothers than we know. There is no current evidence that males have any role in raising the young past fertilization.

Well, I’ve done it again listeners, I have gone over time. I think you can expect that with every episode in this series about bats. If you can’t tell, I do like them a lot. Thanks for joining me for my fourth favorite thing about these amazing mammals, their reproduction.

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

 

Join me next week for another episode about bats!

 

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This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.