Urban effects on native avifauna: a review
Introduction
Urbanization can be defined as concentrated human presence in residential and industrial settings and their associated affects (Cringan and Horak, 1989, Marzluff, 1997), and for the purposes of ecological studies urban centers have been quantified as containing more than 2500 people (Dumouchel, 1975). The urban extent of most metropolitan areas is expanding into adjacent rural landscapes (Alig and Healy, 1987, World Resources Institute, 1994, UN, 1997). With the projected global increase of urbanization, land cover conversions for urban use will only increase altering ecosystem patterns and processes (Grimm et al., 2000).
The factors determining which species can coexist with human settlement include: (1) the presence and patch size of remnant (native) vegetation (Emlen, 1974, Gavareski, 1976, Rosenberg et al., 1987, Mills et al., 1989, Catterall et al., 1991); (2) competition with exotic species that have a longer history of human cohabitation (Major et al., 1996); (3) non-native predators (Churcher and Lawton, 1987, Paton, 1990); (4) the structure and floristic attributes of planted vegetation (Tweit and Tweit, 1986, Green et al., 1989); (5) supplementary feeding by humans (Recher, 1972, Brittingham, 1990, Major et al., 1996); and (6) residual pesticides (Major et al., 1996).
The number of studies that describe avian responses to urbanization is immense and growing (Marzluff et al., 2001a, Marzluff et al., 2001b). For the urban planner, we attempt to summarize into one paper the patterns of avian population and community response to the urban environment by major habitat types. Where possible we illustrate major points with specific species (scientific names in Appendix A) to assist the urban planner and others involved in the planning process to identify local species responses to landscape changes. Next, we review studies that have illuminated some of the major processes that have contributed to the observed patterns of population and community change with urbanization. Finally, we outline future avian research needs that will specifically aid urban planning decisions.
Section snippets
Patterns of urban impacts by matrix habitat type
Total breeding bird density is often higher in urban areas than in the surrounding native habitat (Walcott, 1974, Gavareski, 1976, Lancaster and Rees, 1979, Beissinger and Osborne, 1982). However, species richness is usually lower in urban areas, where the avian community is dominated by a few, often introduced, species (Gavareski, 1976, Lancaster and Rees, 1979, Beissinger and Osborne, 1982, Cam et al., 2000). Urbanization favors a few species but selects against most such that the avian
Urban impacts on raptors
Studies of passerine responses to urbanization are often devoid of important reproductive information that is more descriptive of habitat quality than measures of abundance (Van Horne, 1983). Studies of raptors can be illuminating in this regard, as demographic parameters have often been measured on urban nesting owls, hawks, falcons, and eagles. However, an important caveat is that unlike most passerines raptors may have home ranges that extend beyond the urban boundary and therefore do not
Vegetation changes
There is often a strong positive correlation between the volume and structure of native vegetation and native bird diversity and species richness (Emlen, 1974, Mills et al., 1989). Likewise, non-native species diversity is correlated with exotic vegetation (Mills et al., 1989). Emlen (1974) found that certain native desert birds responded positively to urbanization in Tucson, Arizona, a city that maintains a high proportion of native vegetation. In support of Emlen's assertion, Mills et al.
Conclusions
The effect of urbanization can be immense, yet our understanding is rudimentary. Taxonomically, bird communities in distinctly different habitats are most different in the least disturbed sites and the most similar in the most urbanized sites (Blair, 2001). Urbanization selects for omnivorous, granivorous, and cavity nesting species (Emlen, 1974, Lancaster and Rees, 1979, Beissinger and Osborne, 1982, Rosenberg et al., 1987, Mills et al., 1989, Allen and O’Conner, 2000, Kluza et al., 2000).
Acknowledgements
Carl Bock and Alex Cruz provided helpful comments on an earlier version of this manuscript.
Jameson F. Chace is an assistant professor of environmental studies in the Biology Department at Villanova University. Jim received his M.A. and Ph.D. from the University of Colorado-Boulder studying cowbird-host interactions in Colorado and Arizona at the urban/wildland interface.
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Cited by (0)
Jameson F. Chace is an assistant professor of environmental studies in the Biology Department at Villanova University. Jim received his M.A. and Ph.D. from the University of Colorado-Boulder studying cowbird-host interactions in Colorado and Arizona at the urban/wildland interface.
John J. Walsh is a visiting scientist at the Department of Physical Planning at Alterra, Wageningen, The Netherlands, while concurrently working on his Master's in Urban Planning in the Department of Urban Design and Planning at the University of Washington-Seattle. He received a M.A. in biology from the University of Colorado-Boulder.