The paper in Nature Ecology & Evolution is here: http://go.nature.com/2xMa4FP
Indeed, when we started working in the dry inter-Andean valleys of Bolivia our experience in observing foraging parrots was very small and this lack of experience became our best ally in this study. I think the first time we saw foraging parrots was that of about 60 foraging individuals of Tectocercus acuticaudata apparently preying on Celtis erembergiana fruits. The parrots ate so fast that it was very difficult for us to know if they all ate the same thing and what parts they ate from the fruit.
When they finished, without saying anything, three of us agreed to go and see what remains had left the parrots under the plants. And, truthfully, our complex of ignoramuses was strengthened. Based on our observations we had pointed out that the parrots were predating on Celtis fruits. Underneath the tree, however, there were green fruits predated, ripe fruits in which they had only eaten the pulp, leaving intact the seeds that in very few cases had been predated. There were also many green fruits and some mature whole and with clear signs of being cut by parrots and thrown without eating. From that moment we decided to look under the tree or bush where we observed parrots eating.
The effects of parrots on plant performance can be considerable, as many individuals of Enicognthus ferrugineus in this case, can be observed interacting with a given plant (Ovidia andina).
Weeks later we knew we could trust what we saw on very few occasions. This generally apply when parrots ate pods of some Fabacea and large fruits of several Euforbiaceas or Capparidaceas, but never when they ate medium or small fleshy fruits of species like Ziziphus mistol, Celtis spp, Capparicordis tweendiana and many others with fleshy or dry fruits.
So we decided to overcome the punctures of the spiky scrubs, transform the fear of the stings of pip vipers (Bothros spp) prudently and look for the fresh remains under any tree where the parrots had just eaten. Only thanks to this decision, motivated by our inexperience and the consequent insecurity, allowed us to abandon our initial idea of considering the parrots as exclusively predatory antagonists of the plants from which they fed, to transform it into a more real and complex one that placed them at a variable point in the continuous antagonism / mutualism.
In this picture we see the antagonism-mutualism continum, as the effects of parrots on a given plant can be a mix of seed predation and pulp removal, enhancing germination
This continuum between positive and negative effects on partners can be widely expanded to almost all biotic interactions, and we show that considering this complexity can change our perception about the vulnerability of communities to the loss of their biotic interactions.