Are all patches worth exploring? Foraging desert birds do not rely on environmental indicators of seed abundance at small scales

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

BMC Ecology

Springer

Año: 2019 vol. 19 p. 25 - 35

1472-6785

Background:Consumers should show strong spatial preferences when foraging inenvironments where food availability is highly heterogeneous and predictable. Postdispersalgranivores face this scenario in most arid areas, where soil seed bankabundance and composition associates persistently with vegetation structure atsmall scales (decimetres to metres). Those environmental features should beexploited as useful ´pre-harvest´ information at least to avoid patchespredicted to be poor. However, we did not find the expected spatial associationin the algarrobal of the central Monte desert by observing foraging seed eatingbirds, a field technique influenced by how much they exploit patches. In thiswork we tested if the first stage of foraging by granivorous birds (patchvisit, exploration or encounter) is positively associated with environmentalindicators of patch quality by recording the removal of single seeds from 300 scatteredexperimental devices during seasonal trials. Spatial selectivity was analysedby comparing the structural characteristics of used vs. availablemicrohabitats, and evaluated against bottom-up and top-down hypotheses based onour previous knowledge on local seed bank abundance, composition and dynamics. Theirforaging activity was also explored for autocorrelation and environmental correlatesat bigger scales.Results: Postdispersal granivorous birds were less selective in their use of foragingspace than expected if microhabitat appearance were providing them relevantinformation to guide their search for profitable foraging patches. No kind ofmicrohabitat, as defined by their vegetation and soil structure, remained safefrom bird exploration. Analyses at bigger temporal and spatial scales provedmore important to describe heterogeneity in seed removal. Conclusions: Closeness to tall trees, probably related to bird territoriality andreproduction or to their perception of predation risk, seemed to determine afirst level of habitat selection, constraining explorable space. Then,microhabitat openness exerted some influence on which patches were morefrequently visited among those accessible. Selectivepatterns by birds at small scales were closer to our predictions of a top-downspatial effect, creating or strengthening (and not responding to) the spatialpattern and dynamics of the seed bank.