Effects of farmland heterogeneity at multiple spatial and temporal scales on house sparrow (Passer domesticus) population ecology
Sammanfattning: Strong declines of European farmland birds in recent decades are assumed to be caused by decreased food availability resulting from agricultural intensification and concomitant loss of farmland heterogeneity. One of the species suffering particularly strong declines in NW European countries is the house sparrow. In this thesis I investigated the importance of farmland land-use on house sparrow ecology in Sweden, to determine possible detrimental effects from agricultural intensification and loss of farmland heterogeneity at multiple spatial scales. Because the resident house sparrow depends on food resources being available within a small spatial scale, it may be negatively affected by farm specialisation. Specialisation towards crop production may have reduced insect food available to breeding birds and specialisation towards animal husbandry may have reduced seed availability during winter. I found that house sparrow population declines during 1977-2011 coincided with time periods with strong agricultural intensification, with particularly detrimental effects from farming specialisation. Furthermore, the present day occurrence of house sparrows was negatively linked to farming specialisation towards either crop or live-stock farming compared to mixed farming. Habitat quality during breeding was found to be lower on farms in landscapes dominated by annual crops, compared to those in mixed and live-stock dominated landscapes. House sparrow populations on farms in landscapes dominated by annual crops and mixed farming did not respond to winter supplemental feeding, indicating that they are not mainly food-limited during this time of the year. Intra annual demographic patterns of house sparrow populations situated on farms in agricultural landscapes with differences in intensification and specialization showed patterns concomitant with suggested differences in limiting mechanism, with stronger winter losses on farms in landscapes dominated by live-stock farming, most likely reflecting the lower seed availability in these landscapes. Populations on farms in landscapes dominated by annual crops showed slightly lower population increase during summer, possibly as a consequence of lower insect availability needed during breeding. In conclusion the studies in this thesis indicate that rural house sparrow populations in Sweden suffer from effects of resource separation resulting from agricultural intensification, in particular effects of farm specialisation. Structural change resulting in farm specialisation is very much an ongoing process. To mitigate future declines of house sparrow populations, mixed farming should therefore be promoted.
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