Photos from the Field: Scale-Dependent Spatial Match between Fruits and Fruit-eating Birds

Pedro G. Blendinger et al., (2015). Scale-Dependent Spatial Match between Fruits and Fruit-eating Birds during the Breeding Season in Yungas Andean Forests. Biotropica, 47: 702–711. doi: 10.1111/btp.12247

The multi-scale spatial match between bird and food abundances is a main driver of the structure of fruit-eating bird assemblages. We explored how the activity of fruit-eating birds was influenced by the abundance of fruits at the local and landscape scales in Andean mountain forests during the breeding season, when most birds forage close to their nest. We measured: (1) the spatial scale of variation in the abundance of fruits, (2) the spatial scale of variation in the activity of fruit-eating birds, and (3) the spatial match between both variables. The sampling design consisted of eleven 1.2-ha sites, each subdivided into 30 cells of 20 × 20 m, where we sampled fruits and fruit-eating birds. We found that fruit consumption, and to a lesser extent bird abundance, were associated with local spatial variation in abundance of selected fruit species. However, fruit-eating birds did not modify their spatial distribution in the landscape following changes in availability of these fruits. Our study shows that fruit-eating birds detect local spatial variation in fruit availability in their home breeding ranges, and exploit patches with large clusters of selected fruits. However, it may be unprofitable for breeding birds to stray too far from their nests to exploit fruit-rich patches, accounting for the absence of fruit tracking at larger spatial scales.

Typical landscape of lower montane forest sites located at the bottom of ravines in the Southern Yungas Andean forest. (Photo: Pedro Blendinger).

Typical landscape of lower montane forest sites located at the bottom of ravines in the Southern Yungas Andean forest. (Photo: Pedro Blendinger).

One of the authors (Pedro Blendinger) counting the fruit crop of an epiphytic cactus (Rhipsalis floccosa).

One of the authors (Pedro Blendinger) counting the fruit crop of an epiphytic cactus (Rhipsalis floccosa).

Fruit consumption peaked in small forest patches rich in particular fruit species such us Allophylus edulis, a tree species with large crop size that in addition is selected by fruit-eating birds. (Photo: Pedro Blendinger).

Fruit consumption peaked in small forest patches rich in particular fruit species such us Allophylus edulis, a tree species with large crop size that in addition is selected by fruit-eating birds. (Photo: Pedro Blendinger).

Fruit of Cupania vernalis exposing an arilated seed. The fruits of this species are relatively scarce at the local scale, but still are selected for consumption by birds, even by some with a predominantly insectivorous diet. (Photo: Pedro Blendinger).

Fruit of Cupania vernalis exposing an arilated seed. The fruits of this species are relatively scarce at the local scale, but still are selected for consumption by birds, even by some with a predominantly insectivorous diet. (Photo: Pedro Blendinger).

Turdus nigriceps, one of the main seed-dispersers in the Southern Yungas Andean forest. (Photo: Rodrigo Aráoz).

Turdus nigriceps, one of the main seed-dispersers in the Southern Yungas Andean forest. (Photo: Rodrigo Aráoz).