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The textbook example of commensalism was always the interaction between trees and the birds who make nests in those trees – it was always assumed that the birds gain from this relationships, while the trees are not in any way affected by it.

Now, a new study came out, demonstrating (for the first time, as far as I know – is that correct?), that the relationship between at least some trees and some birds is actually mutualism, i.e., both partners profit from the relationship:

Chickadees, nuthatches and warblers foraging their way through forests have been shown to spur the growth of pine trees in the West by as much as one-third, according to a new University of Colorado at Boulder study.

The study showed birds removed various species of beetles, caterpillars, ants and aphids from tree branches, increasing the vigor of the trees, said study author Kailen Mooney. Mooney, who conducted the study as part of his doctoral research in CU-Boulder’s ecology and evolutionary biology department, said it is the first study to demonstrate that birds can affect the growth of conifers.

“In a nutshell, the study shows that the presence of these birds in pine forests increased the growth of the trees by helping to rid them of damaging insects,” said Mooney. “From the standpoint of the trees, it appears that the old adage, ‘the enemy of my enemy is my friend,’ holds true.”

Hat-tip: Pondering Pikaia.