Foraging habitat selection in the last Ortolan Bunting Emberiza hortulana population in Switzerland : final lessons before extinction

The Ortolan Bunting Emberiza hortulana has suffered a general decline acrossmuch of Western Europe in recent decades. In Switzerland, only one populationremains in sub-Mediterranean shrub-steppe on the south-facing slopes ofthe Rhône Valley (Valais). We aimed to collect data on foraging ecology of thelast Swiss Ortolan Buntings during reproduction. However, this populationunderwent a considerable decline, with no breeding confirmed in Switzerland in2007. We investigated foraging habitat selection of four unpaired males at thehabitat and microhabitat scales, and compared patterns of foraging habitat usewith patterns of terrestrial invertebrate abundance. All radio-tracked birds foragedexclusively on the plain. The adjacent slope, which harboured the formerbreeding grounds, was used only for territorial song displays. All males showeda disproportionate use of conventional maize fields that had been treated withherbicides, while also exhibiting an avoidance of meadows and riparian vegetation.These observed patterns of habitat use may be driven by unavailability ofoptimal foraging habitat, with birds being forced to use the best of a poor set ofoptions. Structurally, it was shown that birds foraged in areas with a high proportionof bare ground, as well as moderately dense overhead vegetation.These areas did not support higher arthropod abundance, suggesting that foodaccessibility (and/or cover) rather than food abundance dictated habitat selection.It remains to be seen whether these patterns of microhabitat use alsoapply to breeding Ortolan Buntings. Further work in southern European breedinggrounds should be envisioned to gain crucial information about the ecologicalrequirements of Ortolan Buntings in Mediterranean and sub-Mediterraneanhabitats. Additionally, effort needs to be focused on identifying factors affectingthe species on the wintering grounds, which may assist in explaining theobserved declines in the breeding areas.