The ingestion of fruits by birds may represent a mutualistic relationship in which they use fruit as nutrient sources keeping intact the seeds. This interaction is described as networks and can present patterns or occurs at random. This
study was designed to determine the network structure and the nestedness of interactions between understory bird assemblies and plants from primary and
secondary forests at Gunma Ecological Park (PEG), located in the Amazonian region. From March to December of 2007, a total of ten expeditions were
conducted for bird capture using mist nets and collection of feces samples for seeds identification. The results were used to determine the connectance,
importance index and the nestedness of the mutualistic system. The nestedness in secondary forest was higher than in the primary forest, and the
net interaction at Gunma Ecological Park was comprised by 37 species (birds and plants) with connectance of 18% and nestedness of 95%. Birds potentially seed dispersers were represented by 20 species, mainly by the families
Pipridae, Tyrannidae, Turdidae and Thaurapidae. Dixiphia pipra was the most important seed disperser species in primary and secondary forest followed by
Lipaugus vociferans in primary forest and Cyanerpes caerulens in secondary forest. A total of 17 plants species were found in the diet of birds. Miconia
ciliata showed the highest importance index because it interacted with 16 bird species,followed by Phthirusa micrantha in primary forest and Euterpe Oleracea
in secondary forest.
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