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

Several of the results provide compelling support to the concept that these fungis are harmful to the ants, states Fran Bonier, a behavior ecologist at Queen’s College in Kingston, Canada. Yet birds use the exact same rhizomorphs on trees that are free of ants too, she states, suggesting that they could additionally profit nests in various other methods.

The ants may supply protection from other killers, but it was unclear to scientists just how the birds maintained them away from their young.

At least 176 bird varieties use fungal rhizomorphs in their nests. Given that regularity, it’s not unusual the scientists located evidence that the rhizomorphs might give some chemical defenses, states Todd Elliott, a biologist at the University of New England in Armidale, Australia. “This raises many questions about the chemistry of what is being launched, and if it is special to this ant and this fungus or whether comparable situations are playing out in other ecological communities all over the world.”

“It seemed extremely unusual to me that the ants did not harm the chicks,” says Rhayza Cortés-Romay, an ecologist at the Universidad Mayor de San Andrés in La Paz, Bolivia. “So I started to believe from the bird’s perspective: How does it accomplish this?”

Throughout the tropics and subtropics, many birds use fungal organs known as rhizomorphs to construct their nests. These cordlike frameworks are formed from millions of densely woven fungal filaments, which the fungi make use of to search for nutrients. In tropical jungles, rhizomorphs grow in the woodland cover, developing complicated networks that catch falling litter from above. Previous study recommends the birds may use rhizomorphs for their strong assistance, antimicrobial attributes and water repellency.

In Costa Rica’s Palo Verde National Park, two bird varieties that live often on swollen-thorn acacias develop their nests practically entirely making use of rhizomorphs of horsehair fungi (Marasmius)– and show up to effectively keep out ants. Behavior and cortés-romay environmentalist Sabrina Amador Vargas of the Smithsonian Tropical Research Study Institute in Balboa, Panama, positioned hairs of horsehair fungus onto the branches of 30 acacia trees populated by one varieties of cooperative ant (Pseudomyrmex spinicola), along with fibers of a nonfungal plant of comparable density and type that birds also use to build nests.

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Swollen-thorn acacia trees are aggressively protected by numerous varieties of ants. It seems that fungal fibers in the nests hinder the ants that encounter them and modify their actions, making them obviously distressed and intoxicated, researchers report in the October Animal Practices.

This yellow-olive flycatcher nest sits in a swollen-thorn acacia tree defended by aggressive ants. The nest is constructed mainly from fungal rhizomorphs, which a minimum of 176 bird varieties make use of perhaps for their durability, water repellency and antimicrobial properties.Sabrina Amador Vargas

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Swollen-thorn acacia trees are strongly defended by numerous types of ants. And yet, a number of varieties of birds across Central America and Africa select to nest in these trees. It appears that fungal fibers in the nests hinder the ants that experience them and alter their actions, making them obviously startled and intoxicated, scientists report in the October Pet Behavior.

In Costa Rica’s Palo Verde National forest, 2 bird species that live typically on swollen-thorn acacias develop their nests nearly entirely using rhizomorphs of horsehair fungi (Marasmius)– and show up to successfully stay out ants. So Cortés-Romay and behavioral environmentalist Sabrina Amador Vargas of the Smithsonian Tropical Research Study Institute in Balboa, Panama, positioned hairs of horsehair fungus onto the branches of 30 acacia trees lived in by one varieties of symbiotic ant (Pseudomyrmex spinicola), together with fibers of a nonfungal plant of similar density and type that birds also use to build nests. The researchers shot the ants to videotape their reactions to the different hairs.

The connection between swollen-thorn acacia trees (Vachellia collinsii) and ants is a symbiotic one. The ants accumulate nectar from the acacia and shelter in its thorns while patrolling the trees like controlling bouncers, attacking and stinging invaders and also trimming or killing trespassing plants. The ants might give protection from various other killers, but it was unclear to researchers how the birds kept them away from their young.

Ants that touched the fungi brushed themselves and accelerated more often than those that touched only the plant fibers, actions suggesting repellence and alarm system. The researchers also detected some extreme behaviors seen nearly solely after call with the fungus, including attacking other ants, spinning and straying around aimlessly and unpredictably. This “alcoholic’s stroll” is evocative ant workers infected by the zombifying fungi Ophiocordyceps and recommends the ants may have been disoriented or ingested toxic substances (SN: 2/21/23).