Bird nests made with a toxic fungus seem to fend off attacking ants

When building a bird nest in ant territory, the best defense may okay be an offensive fungus.

Swollen-thorn acacia trees are aggressively defended by a pair of species of ants. And yet, a few species of birds across Central America and Africa opt to nest in these trees. It seems that fungal fibers all during the nests deter the ants who bump into them and alter their behavior, making them it sounds as if alarmed and intoxicated, researchers report all during the October Animal Behaviour.

“It gave the impression very bizarre to me that the ants did now no longer harm the chicks,” says Rhayza Cortés-Romay, an ecologist at the Universidad Mayor de San Andrés in La Paz, Bolivia. “So I started to think from the bird’s standpoint: How does it accomplish that?”

The relationship between swollen-thorn acacia trees (Vachellia collinsii) and ants is a symbiotic one. The ants collect nectar from the acacia and shelter in its thorns while patrolling the trees like possessive bouncers, biting and stinging invaders and even trimming back or killing encroaching plant life. The ants may provide protection from other predators, nonetheless it indubitably became unclear to researchers how the birds kept them faraway from their young.

Someday of the tropics and subtropics, many birds use fungal organs often is referred to as rhizomorphs to construct their nests. These cordlike structures are formed from millions of densely woven fungal filaments, which the fungi use to try to find for nutrients. In tropical rainforests, rhizomorphs grow all during the woodland canopy, forming complex networks that catch falling litter from above. Previous research suggests the birds may use rhizomorphs for their strong make stronger, antimicrobial features and water repellency.

In Costa Rica’s Palo Verde National Park, two bird species which are living often on swollen-thorn acacias build their nests almost entirely using rhizomorphs of horsehair fungus (Marasmius) — and appear to successfully keep out ants. So Cortés-Romay and behavioral ecologist Sabrina Amador Vargas of the Smithsonian Tropical Research Institute in Balboa, Panama, placed strands of horsehair fungus onto the branches of 30 acacia trees inhabited by one species of symbiotic ant (Pseudomyrmex spinicola), together with fibers of a nonfungal plant of similar thickness and kind that birds also use to construct nests. Then the researchers filmed the ants to record their reactions to the different strands.

Ants who touched the fungus groomed themselves and sped up more often than people who touched only the plant fibers, actions indicating repellence and alarm. The researchers also spotted some extreme behaviors seen almost exclusively after contact with the fungus, including biting other ants, spinning and wandering around aimlessly and unpredictably. This “drunkard’s walk” is harking back to ant workers infected by the zombifying fungus Ophiocordyceps and suggests the ants will have been disoriented or ingested toxins (SN: 2/21/23).

“The primary time we saw the behaviors, we were amazed,” Cortés-Romay says. “These ants are very aggressive. To peer something that affected them in point of fact became a discovery.”

A substantial selection of the consequences offer compelling make stronger to the concept that these fungi are noxious to the ants, says Fran Bonier, a behavioral ecologist at Queen’s University in Kingston, Canada. But birds use the same rhizomorphs on trees which may okay be free of ants besides, she says, suggesting that they'll even benefit nests in alternative routes.

On the very least 176 bird species use fungal rhizomorphs in their nests. On condition that frequency, it’s now no longer surprising the researchers found evidence that the rhizomorphs may provide some chemical defenses, says Todd Elliott, a biologist at the University of New England in Armidale, Australia. “This raises many questions about the chemistry of what's being released, and if it's a prolonged way unique to this ant and this fungus or whether analogous situations are playing out in other ecosystems around the sector.”