BACKGROUND: Frugivorous birds are phenologically linked to the fruits that they eat. When there is less fruit in seasonal environments, frugivorous birds complement their diet by eating invertebrates. The depth of the phenological link between frugivorous birds and their dietary resources has not been studied until now. The objective was to determine the possible phenological synchrony between the Austral thrush (Turdus falcklandii) and its dietary resource, fruits and annelids, found in the fragmented forests in the South of Chile. RESULTS: The numbers of thrushes, annelids, and fruits in fragments of native forest and anthropogenic grassland in Chile's Lake District were estimated annually. Spatial variation (i.e., forest and grassland) and seasonal variation (i.e., the period of greatest fruit growth and least fruit growth) on thrushes, annelids, and fruits were analyzed with a nonparametric Scheirer-Ray-Hare extension for the Kruskal-Wallis test. The graphic representation of the seasonal variation of thrushes, annelids, and fruits was carried out using cubic spline routines. It was found that there are seasonal changes in the dietary resources of these birds. During the period of greatest fruit production, there was a trend towards a higher number of thrushes in the forest where there was a greater availability of ripe fruit in relation to the nearby grasslands. In the grasslands, the annelids demonstrated a trend towards greater quantities in comparison with the forest. There was a positive and significant correlation between the thrushes and the annelids and fruits, indicating phenological synchrony between this bird and its dietary resources. CONCLUSIONS: Therefore, we concluded that the thrush responded numerically and functionally to the variations in its resources. The result of our research underlines the importance of grasslands in maintaining thrush populations, with this bird acting as one of the most important seed dispersers in the temperate southern forests of Chile.