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The Circle of Life on the Eighth Continent

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Ekipa fanihy, the bat team, at play in Ambakoana, District of Moramanga, Madagascar. In back, from left: Rabetsy’fanihy, Cara Brook, Ando. In front: Christian Ranaivoson. November 2013. (Photo by Amelia Yeo)

My third Thanksgiving has come and gone in Madagascar, and I think about my fiainana sambatra—my blessed life—as I explain the American fety to this month’s ekipa fanihy, the bat team. I’ve purchased a live chicken in honor of the occasion, which our masterful mpahandro, Andry, has turned from squawking feathers into fried deliciousness served over steaming rice. I don’t eat meat in America, but it is clearly not the day for that sort of fady, and I ignore my normal dietary restrictions without the slightest misgiving. Most of our meals out here are pure vegan anyway—I feel like this sets the record even. Besides, I reflect, examining my two lean pieces of akoho meat stretched over bone, this barely counts anyway. It’s amazing to me how little food constitutes a feast in Madagascar.

I’m working again in the District of Moramanga, netting flying fox colonies in the Mangoro River Valley, for the third time in what I hope to be a long future of ecological monitoring in this region. Miora is busy with lab analyses in Tana, and Christian and I work instead with the self-proclaimed Rabetsy’fanihy, which translates roughly to “Mr. Betsileo, man of the bats.” Rabetsy was formerly a part of a foreign-funded community monitoring project for Pteropus rufus in the region, and though funding dried up back in 2009, Rabetsy still proudly carries his old identification card. In addition to Rabetsy, we share our table with the Ra’fanihy of the future—young Ando, a simple Mangoro River fisherman, who with us, dons the title of bat catcher, tree climber, and net-maker.

We rise before 3:00 a.m. every morning, crawling out of our tents in the cold, misty moonlight to net flying foxes on their way home from the night’s feeding. Our day starts so early that we usually finish processing the night’s catches in time for our noontime meal—rice and voa maina, or dry beans. In the afternoon, my mpiara-miasa (co-workers) seek out shade in this parched and sun-burned landscape and nap. I’ve never been much good at sleeping, so I study piles of English-Malagasy flashcards, learning increasingly complex words and sentence structures. I write, too, to pass the time, and I read—fiction, non-fiction, novels, short stories, and piles and piles of scientific papers. It’s only recently in my life that I’ve come to enjoy reading science as much as I have always loved literature, and I relish this boundless time to expand my mental horizons.

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Cara Brook with a Pteropus rufus female. Andaparaty, Madagascar. November 2014. (Photo by Christian Ranaivoson)

At dusk, the cycle begins anew. We cast nets for new bats and release the previous night’s catches after they lap up sugar water from our eye droppers with their long, pink tongues. I netted here in early November a year ago when the birth season was just beginning; this year, the females carry larger young than I remember—up to a full third of their body weight. I watch in admiration as the freed females climb high into the trees, infants clinging to their backs and chests, yellow shoulders and brown torsos muscling powerfully upwards into the night. When they let loose from the tree limbs to fly, they drop for a moment before adjusting to the weight of their too-heavy offspring. I have yet to see it, but sometimes, I am told, they can even carry twins. I don’t take tooth samples from these lactating females—these poor ladies have plenty of challenges to deal with already.

Fruit bats typically give birth in a synchronized annual, or bi-annual birth pulse, which has many implications for infectious disease research. Births cause an influx of susceptible young into a population presumably composed of many pathogen-infected, or already-recovered and now-immune adults. When births occur all at once, there’s a sudden influx of new potential hosts in which a pathogen can reproduce itself, and it’s a time for high transmission rates—and, correspondingly, high spillover risk—for many bat-borne pathogens. By contrast, when these births are staggered, as in species like humans with no definable birth season, it can help a pathogen persist in a host population by continually replenishing susceptibles. However, it usually also means that epidemic spikes in infection are rare. In my Madagascar system, I examine inter-species transmission effects on pathogen persistence: Pteropus rufus and Eidolon dupreanum have corresponding birth pulses that might produce epidemic spikes, while Rousettus madagascariensis appears to give birth later, perhaps enabling pathogen persistence.

This picture is complicated by human perturbations in a country where all three fruit bats are consumed for food. Like births, hunting can take place in seasonal pulses—sometimes constrained by the government-regulated legal hunting season (June for Madagascar), sometimes more a product of heightened trapping ease based on local fruit availability. If significant hunting occurs between the birth and mating season, some animals will respond to these population declines by elevating birth rates dynamically—with further implications for disease dynamics. Because they cannot carry much extra weight in flight, bats have trouble mounting these dynamic responses, and more likely, their numbers are just declining. Locally, though, disease might still demonstrate high transmission rates when susceptible young immigrate into now-vacant niche space in a given roost. These patterns have been observed previously with Marburg virus in Egyptian fruit bats and rabies virus in vampire bats.

My adviser once told me that “You don’t really understand anything unless you can write it in an equation.” There are many an artist who might disagree with that statement, and I doubt Andy himself would really defend those words—more likely, he was just not-so-subtly encouraging his graduate student to learn some math. Indeed, in the past few years at Princeton, I’ve found it empowering to think of these seasonal pulses as square curves multiplied by birth and death rates in a differential equation. But there is something truly breathtaking about these wild creatures and their capacity for survival that no equation can capture. I felt it strongest, perhaps, when I radio-tracked wolves in the icy Great North Woods of Minnesota, but I feel it now, too, watching the moonlight glint in the eyes of a furious Pteropus rufus mother. Surrounded as I am by male coworkers, I feel a sudden feminine kinship and a rush of affection for these wild animals and their too-heavy offspring. It’s incredible what Mother Nature has asked them to do.

Christian notices my silence and worries that something is wrong. “Mbola mety ve?” he asks. You still okay?

“Yes,” I say, smiling. “Just thinking.”

“I see,” he answers, then nods gravely. “Always. It is your fomba.

And I do my best to prove him right.

 

Read More by Cara Brook

Comments

  1. Cara Brook
    September 21, 5:00 am

    Thanks for reading, Brian. 🙂 Couldn’t agree more–beautifully put.

  2. Brian Williams
    Geneva and Joburg
    September 21, 4:48 am

    Seeing Andy’s comment on equations I cannot resist adding this from Richard Feynman:
    What it means to really understand an equation—that is in more than a strictly mathematical sense—was described by Dirac. He said: “I understand what an equation means if I have a way of figuring out the characteristics of its solution without actually solving it.” So if we have a way of knowing what should happen in given circumstances without actually solving the equations, then we ‘understand’ the equations as applied to these circumstances. A physical understanding is a completely unmathematical, imprecise, and inexact thing, but absolutely necessary for a physicist.