Licentiate thesis, 2010
Tempo-spatial patterns of foraging by birds in mosaic agricultural landscapesJong, Adriaan de
AbstractMany farmland breeding bird populations decline, while large herbivorous bird species, which forage on farmland outside the breeding period, increase their numbers. Intensification of agriculture causes both processes. Foraging habitat choice was studied in farmland breeding Eurasian Curlews and spring-staging waterfowl, through repeated counts of birds on fields. Foraging Eurasian Curlews shifted from grasslands to tilled, newly sown cereal fields in June, while non-foraging birds did not. The conclusion is that earthworms in dry untilled grassland soils become gradually harder to access for probing birds, while tilled soil remain easy to penetrate. Eurasian Curlews benefit from mosaic landscapes with a mixture of crops, and which offer ample foraging conditions throughout the season. During spring-staging, geese and swans commute between the roost and agricultural fields. Variable selection in hurdle models revealed that field size, distance to the roost and agricultural treatments ley, stubble and unharvested cereal were important for foraging habitat choice, while other agricultural treatments and disturbance were not. Fields with unharvested cereal were, by far, the most attractive. The dataset had high levels of zero-inflation and aggregation, and hurdle models did not fit the data very well. Instead, we created the ADJUN model, which performed better than the hurdle model. ADJUN and hurdle models were used to estimate the coefficients of the important variables. Based on the estimates, we present mathematical formula to calculate the probabilities for presence, and the expected numbers of the four studied waterfowl species on agricultural fields of staging sites similar to the Ume River Delta area. From these studies, I conclude that agricultural treatment is the most important determinant of the quality of a field for foraging birds, and also, that landscape-wide planning of treatment of farmed fields can be an effective tool for bird conservation, and for the reduction of crop damage by birds.
Keywordslic.-avh; charadriiformes; waterfowl; farmland; foraging
Publisher: Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences
Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies
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