Mushrooms with aboveground fruit bodies such as mushrooms or boviste can simply release their spores into the air. In contrast, other mushrooms such as truffles form underground tubers and rely on animals to spread their spores. Until now, it was thought that only pigs and other mammals would eat truffle mushrooms and thus spread their spores with their feces. But now American biologists have discovered that certain South American passerines also feed on mushroom tubers that grow underground and excrete germinable spores. The researchers working with Matthew Smith from the University of Florida documented their discovery in the journal Current Biology.
During a research stay in Patagonia, the biologists observed black-throated and white-throated tapaculos (Pteroptochos tarnii and Scelorchilus rubecula) – two species of passerine birds that are widespread there – foraging. The animals spent hours every day scratching the forest floor and pecking for something to eat: worms, insects, seeds, berries – and even truffles. The researchers observed that the birds exposed and ate truffle mushrooms. This genus, botanically called real truffles, includes many different mushrooms, including the coveted delicacies.
In order to document the unusual diet of the passerine birds more precisely, the researchers collected 169 samples of the birds’ feces. In fact, they were able to detect DNA from various types of truffles in around 40 percent of the samples analyzed. At least half of these spores were still capable of germination.
The authors do not rule out that birds could also contribute to the spread of fungi in other ecosystems in this way. However, it is unclear how the birds find the tubers hidden in the ground. In North America and Europe, pigs and trained dogs help track down truffles that are used in culinary delights by means of odorous substances. For the South American birds, on the other hand, optical signals could also be important, write the study authors. Some of the truffle mushrooms native to Patagonia hardly produce any odorous substances, but their tubers are similar in shape and color to berries that birds also eat. It is possible that the appearance of truffles in this region has changed in the course of evolution in such a way that birds can better recognize and use the tubers as a source of food.