Synurbanization of the magpie in the Palearctic

Abstract

Black-billed Magpie (Pica pica) populations in Palearctic towns have grown dramatically in abundance and density over the last 50 years. Human population growth, largely concentrated in urban areas, has increase anthropogenic foods and reduced potential nest predator density. To examine whether these factors facilitated growth of urban magpie populations, I surveyed breeding magpies in 12 urban and two non-urban landscapes in western Poland and studied the breeding ecology of magpies in the largest of the cities, Zielona Gora, between 1982 and 1996. Magpie abundance increased three times faster in urban than rural settings and breeding success was slightly higher for urban pairs, suggesting that urban population growth resulted from changes in urban landscapes rather than emigration. Growth of the urban magpie population was explained by an increase in suitable, natural nesting substrate and a positive net rate of reproduction. Nest predation was a primary source of nest loss and was negatively associated with nest height. The maturation of poplars planted by urban revitalization projects facilitated nesting. Urban birds also took advantage of the ameleoriated climate and anthropogenic food; they built nests and laid eggs earlier in the year and renested more frequently than rural birds, foraged in the presence of humans, and supplemented their diet with material from open trash bins. The population appeared to be regulated by density dependent juvenile mortality, but the Zielona Gora population continues to grow and maximum breeding population density has not been reported in the literature. Magpies have the ecological and behavioral flexibility to succeed in urban environments. In time, the unique selective environment of urban areas may lead to the evolution of urban-adapted traits in this species.