Homogenizing effects of cities on North American winter bird diversity

Adeline C. Murthy, Trevor S. Fristoe, Joseph R. Burger

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


Urbanization is widespread throughout the United States and Canada. Studies at different scales have shown mixed consequences of urban areas for ecological communities and biodiversity. Here, we use geographic data on urban extent and survey data from the Christmas Bird Count to investigate the influence of urbanization on winter bird diversity over a continental scale. We compared the alpha (local richness) and beta diversity (turnover with distance) of 42 urban bird communities to nearby non-urban communities. We investigated the processes underlying beta diversity between non-urban and urban sites by comparing the frequency of occurrence in species and variability in relative abundances across sites. Alpha diversity was statistically indistinguishable between urban and non-urban sites when controlling for latitude. Community similarity decreased less rapidly over distance in urban compared to non-urban sites, indicating that spatial homogenization from urbanization results in lower beta diversity. Eighteen species of non-native or native generalists occurred across all urban sites, whereas no species occurred in all non-urban sites. Mean-variance scaling of relative abundance shows that species in urban sites maintained similar levels of community dominance across space compared to non-urban sites. The widespread presence of urban species is likely due to similarity in habitats among cities compared to nearby nonurban sites. The decreased variability in relative abundance of urban species is possibly due to urban resource subsidies (e.g., bird feeders, garbage, and irrigation) and shelter (e.g., landscaping, buildings, and microclimates). The increased occurrence of widespread species in cities and less variation in relative abundances across urban sites contribute to the homogenizing effect of cities on avian communities.

Original languageEnglish
Article numbere1216
Issue number1
StatePublished - Jan 1 2016

Bibliographical note

Funding Information:
We thank James H. Brown and Jeffrey C. Nekola for valuable feedback, as well as the UNM Biology Department, Undergraduate Opportunities (UnO) in the Museum of Southwestern Biology, the Audubon Society, an anonymous reviewer, and the thousands of volunteers who contribute to the Christmas Bird Count each year. This project was partially supported by the National Science Foundation Grant NSF-DEB 0731350, and by the Program in Interdisciplinary Biological and Biomedical Sciences (PIBBS) at the University of New Mexico (National Institute of Health Grant T32EB009414). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF or the NIH.

Publisher Copyright:
© 2016 Murthy et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


  • Alpha diversity
  • Beta diversity
  • Christmas Bird Count
  • Cities
  • Citizen science
  • Community similarity
  • Distance-decay
  • Macroecology
  • Species richness
  • Taylor's power law
  • Urban ecology

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology


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