Spatial analysis of sap consumption by birds in the Chaco dry forests from Argentina

MACCHI L; BLENDINGER PG; NUÑEZ MONTELLANO MG

EMU

CSIRO PUBLISHING

Año: 2011 vol. 111 p. 212 - 216

0158-4197

Sap is a high energy resource usually inaccessible to birds, except for woodpeckers that have the ability to drill into living trees. Because spatial patterns of resource availability influence bird abundance, we explored how spatial patterns of sap availability determine the spatial distribution of sap-feeding species in the semiarid Chaco of Argentina. We studied the White-fronted Woodpecker (Melanerpes cactorum), which obtains sap by drilling holes in tree trunks, and the Glittering-bellied Emerald (Chlorostilbon aureoventris)to which sap is available only from active woodpecker holes; another 12 bird species exploited the sap holes. The abundance of tree species used for sap feeding did not explain the spatial patterns of woodpecker groups. Moreover, in each territory woodpecker abundance was centred on a single tree, one that was most intensely used for sap feeding. Abundance of hummingbirds was strongly correlated with the availability of trees with active holes. During the dry season sap is a major component in the diet of White-fronted Woodpeckers and hummingbirds. However, the scale of adjustment of consumers’ spatial distribution to sap availability was species-specific. This species-specific response was closely related to the ecology and life history of the species. The abundance of woodpeckers was determined by very local mechanisms, such as the location of a single sap tree in their small territories, whereas non-territorial hummingbirds were able to track sap wells at scales larger than the territory of a woodpecker group. Results demonstrate the importance of spatial analysis in identifying the ecological determinants of species’ habitat selection and niche differentiation.