Selection of foraging sites by desert granivorous birds: vegetation structure, seed availability, species-specific foraging tactics, and spatial scale

MILESI, F.A.; LOPEZ DE CASENAVE, J.; CUETO, V.R.

AUK

AMER ORNITHOLOGISTS UNION

Año: 2008 vol. 125 p. 473 - 484

0004-8038

Seed availability in the algarrobal of the Monte desert, as in other deserts, is highly heterogeneous at small scales and associated with vegetation structure. Granivores are expected to show a selective use of space (within the capacities of their foraging techniques), resulting in a heterogeneous impact on the seed bank. First, this paper describes the foraging repertoire of granivorous birds in the algarrobal to develop predictions for their expected use of space. Although the granivory guild as a whole tracked the temporal availability of seeds, species within the guild differed in foraging behavior and seasonal changes. Then, selection of space by foraging birds was assessed through a two-scale bird-centered analysis, comparing the distributions of used and available sites. The guild of granivorous birds used the whole range of available micro-sites, though aggregating contrasting partial patterns. Micro-sites with more cover of shrubs, grasses and litter were preferred for pre-dispersal consumption, consistent with the frequent technique of attacking grasses from low woody perches. In contrast, micro-sites used for post-dispersal consumption did not differ from random, suggesting no safe micro-sites for seeds. At a bigger scale not particularly related to heterogeneity in food availability, a selective pattern was clearer: birds avoided meso-sites with low shrub and litter covers, far from trees. In conclusion, patterns are not straightforward and depend on considerations of spatio-temporal scale and species-specific characteristics. Even when predictions seemed clear-cut and were tested with proper scale and target-group, granivorous birds did not select space according to environmental clues of food abundance.