General

Volume 34, Issue 4, Fall 2015

The Bat Approved Diet

By MICHELLE Z. DONAHUE


Gambian epauletted fruit bat
A Gambian epauletted fruit bat (Epomophorus gambianus) eats a fig
on the go, thereby aiding seed dispersal Credit: Merlin D. Tuttle.

Nuts, as we all know, don’t come cheap. But sometimes you just have to have them: All brownies are good, but brownies with walnuts are especially so. And that fun-size Almond Joy from your kid’s Halloween candy stash? It just wouldn’t be the same without its eponymous nut.

In singing the praises of these tasty treats, we’d be remiss not to mention a key contributor that plays a surprising role in getting some of these nuts—and other foods—into your pantry. With all due respect to the honeybee, it’s the bat that deserves our thanks in many cases.

In California’s Central Valley, many nut-producing farms concentrate on a single crop, whether it be almonds, pistachios or walnuts. Sierra Orchards, for example, devotes 95 percent of its 450 acres to walnuts.

But what Sierra has that similar neighboring farms do not are flat, open-bottomed boxes, affixed to barns and tall steel poles. Each of these narrow plywood enclosures houses a group of 100 or so hungry bats, which stream forth every evening to hunt codling moth adults and larvae.

The codling moth is a major pest that feeds on walnuts. Uncontrolled, this same insect that drills holes into apples can destroy as much as 40 percent of a nut crop—a big problem for a state that produces 99 percent of America’s walnuts.

Sierra Orchards
Sierra Orchards, a walnut farm in California’s Central Valley, has
bat houses adjacent to its fields. Each enclosure houses about 100 bats,
which feed on coddling moths and other pests that target the walnuts.
Credit: Merlin D. Tuttle.

Sean McNamara, son of Sierra Orchards founder and owner Craig McNamara, says the farm’s bats are an integral part of the farm’s pest management strategy.

“They consume massive amounts of insects, more than any spray, smoke or mist could ever affect,” McNamara says. “The bats voraciously pursue them.”

Bats in North America are fairly small. At Sierra, the most common are the Mexican free-tailed bat (Tadarida brasiliensis) and the pallid bat (Antrozous pallidus), which weigh about half an ounce and an ounce, respectively. Still, they’re capable of eating up to two-thirds their bodyweight in insects per night; one pallid bat can eat up to 17 grams in one night, about the weight of three nickels.

That adds up fast. If each of the farm’s nine colonies of 120 bats were populated exclusively with pallid bats, they’d mow through four to seven tons of insects annually. That’s the equivalent to the weight of a school bus—in bugs—every single year. And that’s just one crop, on one farm.

The planet’s more than 1,330 known species of bats serve critical roles in bringing all kinds of food to the table, for humans and animals alike.

“Because they’re so secret, we really don’t know the extent of their impact,” says Rachael Long, a University of California cooperative extension advisor who has studied Sierra’s bats. “But encouraging biological control can only add resiliency to any system.”

 

Pollination: Bananas

Gambian epauletted fruit bat
Bats, like this straw-colored fruit bat (Eidolon helvum), have long-
supported the proliferation of wild bananas through both pollination and
seed dispersal. Credit: Christian Ziegler

After you polish off your next ice cream sundae, consider this: Every banana you’ve ever eaten is a hybrid clone. Modern bananas are parthenocarpic, producing fruit without the help of a pollinator. That also makes them genetically stagnant, and thus more easily contaminated.

Having supplanted Gros Michel bananas, which were the standard in the 1950s, Cavendish bananas have dominated the banana landscape for decades. But the ubiquitous Cavendish is succumbing to a deadly fungal disease. Today, scientists and researchers are scouring the tropics for disease-resistant wild bananas that could be crossbred with the Cavendish as a means of saving it.

Unlike modern commercially grown Cavendish bananas, predecessor varieties along with extant wild bananas do require pollination. This important fact explains the conditions under which bats have been romancing bananas for millennia.

Pollen- and nectar-eating bats visit the fragrant, pendulous flowers of wild bananas, transferring pollen as they rub against each new flower. They forage, so the pollen they convey can come from many miles away, ensuring a diverse genetic exchange.

“Many different species of bats are involved in pollination,” says Ivan Buddenhagen, a banana expert who studied bats in Sumatra after retiring from the University of California. “Bananas seem to be adapted to bats by the way the flowers emerge; bats and bananas probably evolved together.”

 Cullen Geiselman, chair of the board of directors of Bat Conservation International, studies bat pollination and seed dispersal in the New World tropics. She notes that bats also genetically strengthen other important species, including baobab, durian and, famously, agave, the plant species from which tequila and mescal is made. 

“Many bats are specialized for moving pollen from plant to plant,” Geiselman says. “There are also probably a lot of plants no one has ever heard of that bats are pollinating. They are maintaining those wild populations.”

 

Seed Dispersal: Fig

Peters dwarf epauletted fruit bat
A Peters’ dwarf epauletted fruit bat(Micropteropus pusilluse) enjoys a piece
of fruit Credit: Merlin D. Tuttle.

But it turns out that these three foods have even more in common: In the New World, all of them rely, in part, on bats to scatter their seed—ensuring their growth in optimal spots and helping to keep forests alive with a diverse mixture of flora.

Figs are particularly important. They’re easy targets for bats, which swoop in, snatch up a plump fruit, then perch elsewhere to devour the pulp. Seeds end up on the ground in one of two ways: spit out as a juiceless nugget, or via airborne defecation. Like birds, bats go on the go, but unlike birds, bats cross open spaces without hesitation. So their guano deposits often land in areas in need of reforesting—sites where species like fig and piper readily colonize.

“Bats are the farmers of the rain forest,” Geiselman notes. “They fly so far, and can be good seed dispersers to help forests regrow. Humans might not notice if we didn’t have bats to disperse certain plants, but on the level of forest regeneration, many animals rely on that, not just people.”

 

 

 

 

 

Pest Control: Cacao

A pallid bat
A pallid bat (Antrozous pallidus) has captured a katydid. Credit: Merlin D. Tuttle.

Deny it all you want, but it’s true: Chocolate is getting expensive. A fussy tree that grows only in a narrow band near the equator, Theobroma cacao seems to be increasingly plagued by a variety of problems—disease and climate change, among others—and supply suffers accordingly. So any additional stress, including crop reduction due to insect pests, drives prices even higher.

In Indonesia, the country that grows a third of the world’s cacao trees, University of Göttingen scientist Bea Maas questioned farmers on what was responsible for controlling insects in their pesticide-free plantations. “Birds” was the unequivocal answer.

Maas suspected bats had a greater role than anyone realized, and that birds received undue credit because of timing. Farmers simply observed more birds because they were active during the day, whereas bats are active at night.

Over a 15-month period, Maas and 46 local helpers set up mesh cages to exclude birds during the day in some areas and bats at night in others. By preventing natural pest control within these cages, insects could devour cacao leaves and buds at will.

Maas found that by excluding birds and bats, cacao yield on the plants in the cages was reduced by 30 percent, with bats accounting for 22 percent of that total. At today’s market cost, that’s a reduction of $520 per hectare; translated to the entire 1.6 million hectares of cacao in Indonesia, that’s a hit of $832 million.

“Bats have a tremendous effect,” Maas says. “Bat conservation is highly important for crop systems all over the world. It’s in the best interests of farmers, but also to people who depend on them for food.”

So the next time you sit down for a meal or dig into your favorite Halloween candy, consider that there’s a very good chance that bats, somewhere in the world, had something to do with how your food got there.

It’s one case where a fly-by-night operation has a very positive—and satisfying—conclusion.

 

To learn more about the Halloween foods bats have a connection with , visit batcon.org/halloween

 

Bats and food

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