Temporal variation in the abundance of two species of thrushes in relation to fruiting phenology in the Atlantic rainforest

Abstract

When fruit resources in tropical forests are scarce, frugivorous birds might track fruiting by expanding their home-ranges or by moving. We tested whether the abundance of the Yellow-legged Thrush (Turdus flavipes) and White-necked Thrush (T. albicollis) is correlated with the fruiting of the dominant palm tree (Juçara Palm, Euterpe edulis) and fruiting within the tree community as a whole in three Atlantic rainforest types (restinga, lowland, and premontane forests) in south-eastern Brazil over 3 years. We monitored abundance of the two species of thrush and their consumption of fruit, and fruiting patterns of Juçara Palms and the tree community as a whole. Juçara Palms accounted for 45 and 28% of the feeding bouts of Yellow-legged Thrush and White-necked Thrush. The abundance of Yellow-legged Thrushes was positively correlated with fruiting of Juçara Palms, but not to fruiting of the tree community, in all forest types. White-necked Thrushes ate a greater diversity of fruits and its abundance was neither correlated with fruiting of Juçara Palms or to fruiting of the tree community. We suggest that fruits of Juçara Palms constitute a paramount food resource for Yellow-legged Thrushes and may influence movement and abundance of the species in different vegetation types and elevations in the Atlantic rainforest, whereas White-necked Thrushes employ other feeding strategies to persist in periods of fruit scarcity.

Additional keywords:

• altitudinal migration
• birds coexistence
• diet
• frugivory
• fruit availability
• resource tracking