The subterranean fungi known as truffles are best known as human delicacy, often sniffed out with the help of trained pigs or dogs. But it turns out these shrooms are popular outside the mammalian world, too: two common birds in Patagonia are truffle hounds in their own right, according to a new study in Current Biology.
The researchers identified a plethora of fungal DNA in the South American birds’ feces, and found that the spores were likely still viable—in other words, the avian gourmands may help the truffles proliferate. The researchers also noticed that some of the brightly-colored fungi closely resembled local berries, perhaps as a strategy to catch the birds’ interest.
“These are really, really common birds that are really widespread over almost the entire area where you find these southern beech forests—and yet nobody has noticed this interaction before,” says study co-author Matthew E. Smith, a mycologist at the University of Florida and curator of the fungal herbarium at the Florida Museum of Natural History. “That suggests that people should be looking at birds as dispersal agents of fungi in other systems.”
Unlike mushrooms that sprout from the ground and shoot their spores into the air, some fungi form enclosed structures called truffles that sit under the leaf litter or in the top inch or two of soil. “The’re basically in a packet [with] a rind around the outside,” Smith says. “Those fruiting bodies are just jam-packed full with spores, and we think the main way they get around is by animals eating them.”
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As the spores mature, many truffles emit strong odors that attract hungry mammals. The fungi often form symbiotic relationships with tree roots, exchanging nutrients they’ve extracted from organic matter in the soil for sugars produced by the plants.
These relationships are important for the southern beech trees that dominate Patagonia’s forests. However, the sorts of ground-dwelling mammals that would typically spread truffle spores around are sparse. More common are several birds that forage on the ground, including the black-throated huet-huet and chucao tapaculo. These critters aren’t too picky about what they eat; they’ve been documented feasting on worms, slugs, and other invertebrates as well as fruits and seeds, Smith says.
While hunting for truffles for a research project on fungal diversity, Smith and his colleagues started to witness some unexpected behavior. After the researchers finished raking through the leaf litter and moved on, the birds would approach and poke through the disturbed area. One intrepid bird followed Smith around for hours. “It was interested in what I was finding in the soil,” he says. “That was weird; I had never seen anything like that before.”
Smith and his team also realized that several purple and white fruits at these sites looked so much like local truffle species that it was difficult to tell them apart. They suspected that this was no coincidence. Birds often rely on vision rather than their sense of smell to find food; a berry-like appearance could give the truffles a better shot at being consumed.
What’s more, the researchers found what seemed to be the remains of a few fungal feasts. “We sometimes would find truffles with big peck marks in them,” Smith says. “It looked like a chicken had come along and plunged its beak into the truffle several times.”
He and his colleagues decided to investigate. They collected more than 100 fecal samples from across 700 kilometers (435 miles) in Chilean Patagonia—in some cases holding the birds in cloth bags until they pooped—and tested them for fungal DNA. Among the wealth of genetic material were 45 truffle species, including several that haven’t yet been properly described and named.
The researchers also observed that both the black-throated huet-huet and the chucao tapaculo had fungal communities in their feces that differed from those found in the soil where they’d relieved themselves. This supports the idea that the birds help the fungi they eat disperse into new places.
Smith and his team then examined the poop samples under a microscope to get a closer look at the truffle spores within. About 50 percent of the spores were intact after their journey through the birds’ digestive tracts, suggesting that they were still alive and could sprout anew elsewhere.
“Basically everywhere we went where we could find the birds, we found evidence that they were eating fungi,” Smith says. One member of the team even witnessed a chucao tapaculo gobbling up a truffle.
Scientists have often assumed that birds mostly turn to fungi only if their preferred meals aren’t available, Smith says. However, the new findings suggest that, at least for these two Patagonian species, truffles regularly make it onto the menu.
“We don’t know how much this applies to other places until people look,” Smith says. “It could be that Patagonia is quite unique in this way.” However, he says, it’s more likely that birds play an important role in spreading fungal spores in other habitats around the world.
“The first place I’d look is other birds that are on the ground eating all sorts of things,” Smith says. “They’re probably eating truffles in those systems too and it just hasn’t been observed.”
The researchers next plan to explore how much nutritional value different truffle species offer the birds, and whether they actually prefer the fungi over grubs and other common foods.
Bird populations in Patagonia are increasingly threatened by the fragmentation of their forest habitats, Smith and his team noted in the paper. Understanding the connections between birds, fungi, and trees will be vital for future conservation efforts, he says.
