Non-maternal allogrooming of pups

We have four new vampire bats. The bats here at the field station have been breeding in captivity, which is a good sign that they are doing well, and it ensures we have some highly related dyads for our experiments. My first intern, Jana, just took this neat video of a mother and her new pup being groomed by another female. I don’t know yet if this is a relative of the mom, but I will after I genotype everyone. This non-maternal (even non-kin) allogrooming of young pups is not uncommon in vampire bats, and I wonder if there’s an analogy to the common phenomenon of infant handling in primates.  I sped up the video except for some of the allogrooming.

The pups are born with open eyes and the ability to scramble around pretty well. The gestation period is about 7 months–pretty long! Pups grow quickly from about ~6 grams at birth to ~12 g in about 3 weeks, and ~24 g in 3 months. But the pups start out with big, almost fully-grown, feet! Adorable.

Pups also depend on their mothers for a longer period than other bat species. And for female pups, maternal care extends into an enduring mother-daughter relationship that can last many years.

In captivity, the mothers will carry their pups around while nursing them for 2 months, when the pups weigh roughly half their mother’s weight. At 4 months, the pups are flying around and drinking blood, and I’ve seen a 5-month-old juvenile regurgitate food to her mother!

Mothers stop providing milk to pups at about 10 months, after they have gradually switched them from milk to regurgitated blood. Wilkinson observed a mother regurgitating blood to her pup within minutes of its birth, which may inoculate the pup’s intestinal microbiome.  Pups are fed with regurgitated blood primarily by their mother, but increasingly also by other groupmates, especially maternal kin. Both Uwe Schmidt and I have even seen vampire bats fed by related males, such as a father or older half-brother.

Allonursing happens in captivity, although Jerry Wilkinson never observed it during his 400 hours of observation in the wild. Uwe Schmidt’s lab observed an orphaned vampire pup that was adopted by a non-lactating female. After a few days, the foster-mother began lactating and raised the adopted bat successfully [1]!

Female bats become sexually mature after their first year [2], and there is no strict reproductive season. A female can produce a new offspring about every 10 months, and individuals can live to be more than 30 years old in captivity [3]. In the wild, there are records of bats surviving at least 15-17 years [4-5]. This suggests that a female vampire bat could have have more than 20 descendants in her lifetime despite such an extreme life history strategy of high investment and slow reproduction.

Interestingly, at the captive colony I studied at Organization for Bat Conservation in Michigan, several females had very high reproductive success, while other females had no pups at all during the same 4-year-span. Given the huge geographic range of vampire bats, and given that these low-fitness females tend to come from different source populations, one explanation is that the males and females may have been sourced from wild populations that are too genetically distant.

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References

1. Schmidt, Christel. 1988. Reproduction. In: Natural History of Vampire Bats, edited by Greenhall, AM and Schmidt U. CRC Press. (And refs therein)
2. Wilkinson, G. 1985. The social organization of vampire bats I and II. Behavioral Ecology and Sociobiology.
3. Me. 2012. the oldest vampire bat. socialbat.org https://socialbat.org/2012/08/22/the-oldest-vampire-bat/ (and refs therein)
4. Tschapka, M., Wilkinson, G.S. 1999. Free-ranging vampire bats (Desmodus rotundus, Phyllostomidae) survive 15 years in the wild. Z. Säugetierkunde, 64, 239-240.
5. Delpietro, H. A., Russo, R. G., Carter, G. G., Lord, R. D., & Delpietro, G. L. 2017. Reproductive seasonality, sex ratio and philopatry in Argentina’s common vampire bats. Royal Society Open Science, 4(4), 160959.