Evidence indicates that populations of house sparrows (Passer domesticus) have declined radically throughout western Europe over the past decades. A study is described in which researchers utilized a combination of field experiments, genetic analysis, and demographic information to conclude that a reduction in winter food supply resulting from agricultural intensification is probably the primary reason behind widespread local extinctions of rural house sparrow populations in southern England. Findings from the study indicated that farmland populations are characterized by fine-level genetic structuring. Certain population are unable to sustain themselves (sinks), while other populations serve as sources. Implications of these findings are discussed.