Girl Bats Feel Colder Than Boy Bats, New Study Shows

Not only women but some female birds and animals also feel colder than males of the species – and it may save their lives, Tel Aviv University discovers

Ruth Schuster
Ruth Schuster
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Two mousetail bats in a cave in Israel. The female is the one talking about how cold it feels.
Two mousetail bats in a cave in Israel. The female is the one talking about how cold it feels. Credit: Eran Levin
Ruth Schuster
Ruth Schuster

Lady bats feel colder than male bats, according to researchers at Tel Aviv University. In fact, this sensory bifurcation appears to exist in many species of aviating mammals, and birds as well. Dear men, it’s real: Women feel colder than you; we’re not just complaining about the air-conditioning because it’s fun.

What’s more, experiencing temperature differently may save the female bats’ lives, and this likely applies to all the many species in which this temperature-experience differential apparently exists, hypothesizes Dr. Eran Levin of Tel Aviv University. He is the co-leader of the study published in the journal Global Ecology and Biogeography, with Dr. Tali Magory Cohen from Tel Aviv University, Yosef Kiat from the University of Haifa, and Dr. Haggai Sharon, a pain specialist at Tel Aviv University’s Sackler Faculty of Medicine and the Tel Aviv Sourasky Medical Center.

A pain specialist sounds apposite given how sore a point the ambient temperature of a room can become, but actually there was another reason for her inclusion. We’ll get to that.

How did this realization that female bats and mice and birds and others prefer warmth, while the male thrives in the cold, dawn on science? No, it isn’t that science decided 4 billion women can’t be wrong. It’s that the researchers looked at bats and birds living in Israel, reviewed the scientific literature, and noticed a pattern that had been observed before but never adequately explained.

In the first week of April, the mousetail bat mates, says Levin, who is, among other things, an expert on bats. This is no coy boy-bat-meets-girl-bat; this is a raging orgy in a specific cave in the Judean Desert. This cave is pretty inaccessible, he adds, so don’t bother looking for it to get for ideas.

After a week or so of sex, the male bats and female bats part ways. The males go to cooler areas, but the females head for warmer climes.

“Entire colonies in caves on the slopes of Mount Hermon are composed of only males during the [post-] breeding season, while in the warmer area of the Sea of Galilee there are mainly females,” Levin says. After four months of gestation, they give birth in July and raise the pups there, the team explains.

Yes, the females bring up the baby bats alone, and then roughly at the same time as the school year starts, all the bats – the females, males and babies – migrate to nice warm caves, where they undergo a sort of Israeli version of hibernation.

Which means what? That the temperature inside the caves is about 20 degrees Celsius (68 degrees Fahrenheit), not exactly like the arctic blasts that have bears and other animals sleeping through the winter in the far north. But the bats spend about five months in those caves without leaving them. They do not drink or eat in this time, Levin says.

Apologies to anyone who doesn't like bats for the nightmares this image will trigger.Credit: Eran Levin

During this hiatus, they are awake in some fashion; they will move around the cave, and never shut their mouths. They chatter nonstop: speech in bats has already been studied separately; but their metabolism measures all-but-dead, Levin explains. And then after five months, the males regrow their testicles, which are absolutely enormous…

What? They do what? What happened to the testicles they had? Wait. Before getting to their gonads, why don’t they eat or drink for five to six months? It’s Israel, the weather outside is great most of the time.

“I think it’s because they can,” Levin suggests. “If for half a year they can fast and not leave the cave, they avoid the risks of being injured or eaten – well, that’s great.”

And the testicles? When the male bats finish mating, their testicles sort of disappear, and this is a good thing for a flying animal with gigantic balls, he explains. And then come mating season, their maleness reappears – and it is indeed an impressive sight.

Before we get down to why all this makes evolutionary sense, how is it that after a year stuck at home with COVID lockdowns and whatnot, we turned into potatoes, but the bat shakes itself after six months of doing nothing but grousing, and flies off – a strenuous effort if ever there was one? How do they maintain muscle condition? How do bears manage it after sleeping through a winter? We don’t know. Science is looking into that, Levin says. Moving on.

All bats do it

While the team has only researched this in mousetail and other Israeli bats, they have observed it in all other bats in Israel and the literature reports sexual segregation in bats around the world, Levin says, including in North Dakota and Italy.

How did they come to realize that the segregation was because the ladies felt cold, or preferred warmth (call it what you will)? “I wondered in mousetails why they split up, and checked tons of parameters and only thing I could find is the temperature difference,” Levin explains. And then he went back to the literature on human beings. “There are thousands of articles about this and nobody could explain it,” he says. Some expected that muscle mass was relevant, but it wasn’t; muscular women are just as sensitive to cold as other women, and weedy men like the cold as much as the bully on the beach.

Mousetail bats in a cave. The male is the one holding the remote for the AC.Credit: Eran Levin

The team also found numerous articles on sex segregation in other animals, which the researchers surmised might be due to food or competition.

At this point, co-lead author Tali Magory Cohen did a spatial model factoring in all the known parameters based on a database of all birds and bats in Israel, and the eureka moment arrived.

The model showed one thing in common: temperature differences.

In mice, for instance, the team observes that captive females cluster in groups, creating great piles of lady mice, and keep one another nice and warm. Male mice are on their own, and it isn’t because they’re creeps or testosterone-mad; castrated male mice do the same.

Which is where the Sourasky pain expert, Dr. Sharon, enters the research. It turns out that males and females experience temperature much like pain: differently.

Why would all this happen? “We claim it has an evolutionary advantage: it causes separation between males and females, and that’s great except when actually breeding,” Levin explains.

Bats, bats, bats.Credit: Eran Levin

It is? Yes, it diminishes the competition over food and resources, which get hogged by males, he says. “It protects the females from male aggression,” he sums up.

In more evidence that males and females feel cold differently, the team points out that in at least some migratory bird species, males spend the winter in colder areas than females – but note that in contrast to the bats, they tend to stick together when breeding.

The male birds in some species help rear the chicks; and, in a final note, the lady birds bask in the sun more than the males do, when given their druthers. The males will live on the mountain peaks and the females in the valleys. Since the lady bats can’t put on a sweater, when they don’t need to breed the sexes tend to stay apart and temperature has been the only parameter shown to be consistent in the species that were examined.

Maybe this information on shivering lady bats will help men accept that the women in their lives suffer from the arctic blast emanating from the air conditioner. At least we on the female continuum have Transportation Minister Merav Michaeli on our side: she announced in July, shortly after taking office, that “women always feel colder than men” and set out to raise the temperature in train cars because it’s great for the guys but freezes the gals. She wants it to be comfortable for everybody, according to Ice.

That may, however, have to involve somebody moving into a cave.

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