Does urbanization select for weak competitors in house sparrows?

Abstract

How urbanization affects animal populations is in the focus of current ecological research. Existing theory of this topic suggests that the cities' more constant food supplies and lower predation pressure lead to a high proportion of weak competitors in urban populations. To evaluate this hypothesis, we tested whether competitive performance differs between differently urbanized populations of house sparrows Passer domesticus. We previously showed that wild urban sparrows are smaller and leaner than rural conspecifics, and this difference persists for months under identical captive conditions. Here we compared several aspects of their competitiveness (fighting, scrambling and searching for food) in captive mixed flocks of urban and rural birds. We found that sparrows exhibited consistent individual differences in competitiveness, but these differences were not related either to the degree of urbanization of their original habitats or to their body mass. Moreover, the variance in competitive abilities also did not differ between birds from more and less urbanized habitats. Thus our results did not support the hypothesis that urbanization shifts population structure towards an over‐abundance of weak competitors in house sparrows. We discuss possible explanations why sparrow populations may not differ in competitiveness despite the smaller body mass of urban birds.

Urban Great Tits (Parus major) Show Higher Distress Calling and Pecking Rates than Rural Birds across Europe

“…In line with this finding, elevated levels of male territorial aggression have been found in urban song sparrows Melospiza melodia, compared to rural male conspecifics. However, this pattern is not necessarily supported in other species (Newman et al, 2006;Bókony et al, 2010;Atwell et al, 2014;Hasegawa et al, 2014). Furthermore, bird species living in urban landscapes have been shown to peck in lower frequencies in response to handling than those inhabiting rural habitats (Møller and Ibáñez-Álamo, 2012).…”

Habitat urbanization and its effects on birds

“…Likewise, studies of the house sparrow found no evidence of any systematic, urbanization-related differences in stress responses, physiology, coloration, or body condition of adults, although birds of urbanized habitats were found to be proportionally smaller (but not leaner) compared to their rural conspecifics (Liker et al 2008. In another study, urban and rural sparrows neither differed in their competitive performance, nor did the authors found any relation between individuals' body mass, competitive success or in variance of competitive abilities (BÓkony et al 2010). Similarly, a recent study on the song sparrow failed to find detrimental effects of increased habitat urbanization on birds' stress physiology and body condition (Grunst et al 2014).…”

Differences in biometry and body condition of the House Sparrow (Passer domesticus) in urban and rural population during breeding season

“…Also, the competition for resources in large populations has not been confirmed to be the reason behind the weaker condition of the urban House sparrows, which has been proven in an experiment conducted in a mixed flock of sparrows from urban and rural areas. These birds, kept in captivity under the same conditions and under the influence of various factors, showed no differences in their ability to compete (Bókony et al 2010).…”