The love lives of bats

Hi everyone! This week’s post will cover the sauciest topic of bat science – bat reproduction! This coincidentally coincides with the start of August, which is the beginning of the mating season for the bats in the UK!

Most bat species have a polygynous mating strategy1. This means one male will try and mate with as many females as possible. He then has nothing more to do with his pups1. Usually, with polygynous animals, the females end up being super choosy with who they mate with. So before any of the fun can happen, he has to go ‘on the pull’. Here are some of the wonderful ways male bats can score:

Sexy squeaks

Female Mehely’s horseshoe bats prefer higher-pitched males

Ultrasonic squeaking is not just for finding food, but can also allure females in a charming serenade. If you happen to be a male Mehely’s horseshoe bat (Rhinolophus mehelyi), you’ll get more female attention if your song is higher pitched2*. Or perhaps, if you are a male greater sac-winged bat (Saccopterus bilineata) or a Seba’s short-tailed fruit bat (Carollia perspicillata), your serenade will be long, complex and unique to you3,4. We still don’t know much about batty serenades, and this sort of signalling in nature has loads of awesome avenues to explore such as how a male learns his song, which songs are most successful, and what function does song complexity serve?

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* – The females would be more a fan of the BeeGees of the bat world, than the Barry White’s. Sorry, Barry…

Alluring leks

Male hammerhead fruit bats line up along river banks and honk at females, who then choose who to mate with

Lekking is quite rare in bats, and is more common in birds. A lek is when loads of males come together, in visual or auditory range of one another, and show off to the females*. The result is a plentiful buffet of potential mates laid out for the females to take their pick from. If you are a male Hammerhead fruit bat (Hypsignathus monstrosus), the best way to get a lady bat interested is to line up with other males, usually along a river, making enormous honking noises and flapping your wings5. They are the only species of bat that definitely lek, but a couple more species exhibit some lek-like behaviour that’s sort of lekking but not quite6.

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* – It’s also important that the area where the lek forms does not have many resources on it, either. For something to be officially a lek, there are lots of boxes to tick!

Exciting epaulettes

Male epauletted fruit-bats will flash the females with their charming shoulder tufts in an attempt to woo them

It’s not just male birds who can dazzle the ladies with their colourful bodies, bats can too! Epauletted fruit bats have pale tufts of fur on their shoulders called epaulettes. When the males beat their wings and stretch specific muscles, these tufts become more visible and so are thought to attract females7.

Dirty dancing

Male greater sac-winged bats impress the ladies with agile aerobatic displays

If you’re a female bat with a taste for aero-bat-ics then look no further than the swooping, soaring male greater sac-winged bat (S.bilineata)4,8! Whilst it’s likely more species perform aerial courtship displays (‘dancing’ on the wing to impress the girls), this species in particular has been the most studied. Researchers have also found that the smaller, more symmetrical bats, are more agile in the air and therefore dance the best, winning more females8. This is a nifty example of reverse sexual size dimorphism*, where, unusually for mammals, the females are larger than the males.

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* – Sexual dimorphism is the difference in shape between males and females

Saucy smells

Female greater sac-winged bats will choose a mate based on the bacteria he cultivates in his wing pouch

And once more, we return to the greater sac-winged bat. It’s either that this bat is just the king of flirtation methods, or that it was just quite common and therefore easy to study! That aside, this is one of my favourite bat courtship behaviours: male greater sac-winged bats will fill the small sacs on their wings with “genital and gular secretions”9*. This creates a bacterial soup that is unique to each male bat9, and this is where it gets cool. We think the bacterial soup smell tells the females a lot about a males immune system. For her to have healthy offspring, she wants to find a male with an opposite immune system to hers†. When the male rubs his bacterial soup sacs on her, she can determine if his immune system is a good opposite to hers, and then decide to mate! Besides being a little bit gross, isn’t that just amazing?! Kind of like a more efficient smell-based Tinder for bats! Of course, I’m not sure if this has been confirmed for certain, but something similar to this has been found in humans10 – an excellent experiment to read about if you have time.

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* – I’ll leave you to look up what that means

† – This will mean her babies can fight more illnesses as they have a larger variety of genes. Think of it as a two puzzle pieces fitting together because their edges are opposites of each other – the result is you get a larger piece of puzzle, covering more ‘illness ground’. The official term for mating with someone with an opposite trait to you is ‘disassortative mating’

And… cheating

 If you decide you can’t be bothered wooing the choosy females, you can just cheat. Many bats, like a lot of mammals, hibernate during the winter. As they are getting ready for hibernation, however, they enter a semi-hibernation state which is like a very deep sleep where you get quite cold. This is called torpor, and a few male bats take advantage of this. Some do mate with torpid females1,11. Pretty grim.

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So there is a summary of some of the fancy, unhygienic or damn-right grim ways you can obtain a mate if you’re a male bat. Some bats, unusually for mammals, do practice monogamy (mating with just one partner), such as the lesser sac-winged bat (S.leptura) or the grey-headed flying fox (Pteropus poliocephalus)*. There is even an interesting paper exploring homosexuality in bats12. After mating, bats will usually have one pup a year, although some bats like the Eastern red bat (Lasiurus borealis) will have quadruplets1†!

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* – although, having said that, mating systems are a bit of a spectrum and some individuals will be a bit promiscuous

† – this is crazy when you think that these bats sometimes have to carry their young whilst flying!

So as the bat mating season begins in the UK, I hope this post has provided some useful advice and tips for any male bats out there that might be reading this, provided they don’t cheat!

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  1. Taylor 2019 | ISBN: 978-1-78240-557-3
  2. Puechmaille et al. 2014 | DOI: 10.1371/journal.pone.0103452
  3. Behr & von Helversen 2004 | DOI: 10.1007/s00265-004-0768-7
  4. Knörnschild et al. 2014 | DOI: 10.1163/1568539X-00003171
  5. Bradbury 1977 | DOI: 10.1111/j.1439-0310.1977.tb02120.x
  6. Toth & Parsons 2013 | DOI: 10.1111/jzo.12069
  7. Wickler & Seibt | DOI: 10.1111/j.1439-0310.1976.tb00941.x
  8. Voigt et al. 2005 | DOI: 10.1007/s00265-004-0874-6
  9. Voigt et al. 2005 | DOI: 10.1644/1545-1542(2005)086[0745:BBABSS]2.0.CO;2
  10. Wedekind et al. 1997 | DOI: 10.1098/rspb.1995.0087
  11. Hosken et al. 1997 | DOI: 10.1098/rspb.1997.0055
  12. Riccucci 2011 | DOI: 10.4404/Hystrix-22.1-4478

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