Ants have a reputation for ruining picnics. Well, being a bird in an ant-infested tree is no picnic, either.
Scientists watched birds foraging in trees in shade coffee plantations in Mexico. The Azteca instabilis ant lives in certain trees in the canopy where it forages for insects.
Birds did not avoid the trees, but when the ants were active they did not stay very long. The ants can be quite aggressive and may have been protecting themselves or access to their insect prey.
This article summarizes the information in this scientific paper:
Philpott, S. M., Greenberg, Russell S. and Bichier, Peter 2005. The influence of ants on the foraging behavior of birds in an agroforest. Biotropica, 37: 467-470.
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