High urban population density of birds reflects their timing of urbanization

Abstract

Living organisms generally occur at the highest population density in the most suitable habitat. Therefore, invasion of and adaptation to novel habitats imply a gradual increase in population density, from that at or below what was found in the ancestral habitat to a density that may reach higher levels in the novel habitat following adaptation to that habitat. We tested this prediction of invasion biology by analyzing data on population density of breeding birds in their ancestral rural habitats and in matched nearby urban habitats that have been colonized recently across a continental latitudinal gradient. We estimated population density in the two types of habitats using extensive point census bird counts, and we obtained information on the year of urbanization when population density in urban habitats reached levels higher than that of the ancestral rural habitat from published records and estimates by experienced ornithologists. Both the difference in population density between urban and rural habitats and the year of urbanization were significantly repeatable when analyzing multiple populations of the same species across Europe. Population density was on average 30 % higher in urban than in rural habitats, although density reached as much as 100-fold higher in urban habitats in some species. Invasive urban bird species that colonized urban environments over a long period achieved the largest increases in population density compared to their ancestral rural habitats. This was independent of whether species were anciently or recently urbanized, providing a unique cross-validation of timing of urban invasions. These results suggest that successful invasion of urban habitats was associated with gradual adaptation to these habitats as shown by a significant increase in population density in urban habitats over time.

Brain size and urbanization in birds

“…This operational definition is similar to that provided by Klausnitzer (1989), Gliwicz et al (1994) and Stephan (1999). We used two criteria for defining successful urbanization: (1) Higher population density of breeding birds in urban than in nearby rural habitats, and (2) timing of urbanization (Møller et al 2012). …”

Are urban areas suitable for thermophilic and xerothermic bee species (Hymenoptera: Apoidea: Apiformes)?

“…This is a current subject of research, which is confirmed by the regular appearance of studies on urban fauna including pollinating insects (Germanie and Wakeling 2001;McIntyre and Hostetler 2001;Zerbe et al 2003;McFrederick and Le Buhn 2006;Matteson et al 2008;Indykiewicz et al 2011). A general pattern established during the last decades shows differences between urban and surrounding rural areas (Møller et al 2012). Nevertheless, there is still a lack of basic knowledge of the ecology of urban ecosystems.…”

Animal cognition in a human-dominated world

“…Conversion of natural habitats to cities, the fastest form of planet wide environmental change currently (Angel et al 2011), provides animals with overabundant year-round food resources, nesting opportunities and, according to some, seasonally dampened, more homogenous, predictable environmental conditions, along with protection from predators (Shochat et al 2010). Under these conditions, the density of some avian populations has been found to be on average 30% higher in urban than in rural habitats and as much as 100-fold higher for some species (Møller et al 2012). Large-scale land clearing to increase grazing opportunities for cattle, coupled with installation of permanent water holes, has created ideal ecological conditions for large grazing marsupials, such as the Australian eastern grey kangaroo (Macropus eugenii), whose Queensland populations exploded from 11 to 23 mio in just four years prior to the instigation of commercial harvesting in 2004 (Australian Government 2013).…”