Abstracts from the symposium at the 117th Stated Meeting of the American Ornithologists' Union, Ithaca, NY, 14 August 1999:
Urbanization and birds: Impacts at multiple ecological scales.
Organizers: Reed Bowman and Kevin McGowan.
Introduction to urban bird studies: An historical perspective. REED BOWMAN*, Archbold Biol. Sta., Lake Placid, FL, JOHN M. MARZLUFF, Coll. For. Res., Univ. Washington, Seattle, WA, and KEVIN J. McGOWAN, Sec. Ecol. & Syst., Cornell Univ., NY.
Urbanization is a process in which natural landscapes are altered to landscapes of degraded habitats, dominated by human uses, that are impervious to natural ecological processes. Urban habitats are the human-dominated terminus of a gradient from wildlands, through rural, suburban, exurban habitats, to urban, metropolitan centers. A relatively long history of research examining the impact of urbanization on birds exists. Just in the last decade over 50 papers have been published on the impacts of urbanization on birds. However, urbanization has outpaced research and large gaps still exist in our understanding of the effects of urbanization on birds. Many of the avian community changes that accompany urbanization have been described, but higher-level community interactions and, especially, the effects that occur at the population level and even at the level of individuals that contribute to community-level changes are less well understood. Previously we convened a symposium at the 1999 Cooper Ornithological Society meeting that discussed the methodology of studying urbanization effects on birds and reviewed current empirical work. Here, we focus on current research that examines these effects on avian communities, populations, and individuals that integrate theoretical and applied perspectives. This integration may lead to new insights that help us mitigate the deleterious impacts of urbanization and understand how birds react to extreme ecological change associated with our urbanizing world.
Demographic and behavioral comparisons of urban and rural American Crows in New York. KEVIN J. McGOWAN, Sec. Ecol. & Syst., Cornell Univ., NY.
American Crows have been using urban environments for roosting and breeding in recent decades. I have studied crows in upstate New York since 1989, and compared reproductive success, survival, and social behavior of crows in urban and rural areas. Although both urban and rural crows maintained permanent territories, urban American Crows had smaller territories and nested at higher densities. Group size and the presence of helpers at crow nests did not differ. Birds raised in one habitat tended to breed in the same habitat. Nest success was equal between the areas, with similar success rates at each stage of the nest cycle. Survival of crows post fledging did not differ between the habitats. Rural nests produced 1 more young per successful nest and significantly larger young than urban crows, indicating that food resources were better in rural areas. Data from a drought year, a time of apparent food shortage, indicate that urban food resources also are less dependable than those in rural areas.
Causes and consequences of expanding American Crow populations in urban environments. JOHN M. MARZLUFF*, Coll. For. Res., Univ. Washington, Seattle, WA; RICHARD L. KNIGHT, Dept. Fishery & Wildlife, Col. State Univ, Ft. Collins, CO; KEVIN J. McGOWAN, Sect. Ecol. & Syst., Cornell Univ., Ithaca, NY; CAROLEE CAFFREY, Dept. Biol., Oklahoma State Univ., Stillwater, OK; and ROARKE E. DONNELLY, Coll. For. Res., Univ. Washington, Seattle, WA.
We pooled results from our studies of American Crows in a number of settings (Seattle, WA; Olympic Peninsula of Wa; Encino, CA; Ithaca, NY; Madison, WI; and Stillwater, OK) over a variable number of years from the mid 1980's to late 1990's (studies are ongoing and have ranged from 3 to 10 yr in duration) to: (1) quantify trends in crow population numbers, (2) quantify use of space, survivorship and productivity of crows in areas of varying urbanization, (3) speculate why crows appear to be so successful at colonizing urban areas, and (4) determine the effects of crows on other birds. Crows increase in abundance from wildland to urban core study areas in western Washington and are rarely found >5 km from human activity centers in wildlands. Our studies indicate that: (1) size of breeding range is usually <15 ha in urban areas, 30 - 40 ha in rural/urban interface areas, and 1000-3500 ha in wild settings; (2) reproductive success is not consistently related to degree of urbanization, but it is limited primarily by nest predation; (3) mortality of breeding crows is exceptionally low (<5% per year) across the urban gradient; (4) the abundance of crows in forested settings does not correlate with the rate of nest predation experienced by songbirds nesting there.
Synthesis, opportunities and future directions. KEVIN J. McGOWAN*, Sec. Ecol. Syst., Cornell Univ., Ithaca, NY, JOHN M. MARZLUFF, Coll. Forl Res., Univ. Washington, Seattle, WA, and REED BOWMAN, Archbold Biol. Sta., Lake Placid, FL.
We conclude the symposium on the impacts of urbanization on birds by synthesizing the main points made by today's speakers and suggesting that this field of research offers multiple opportunities for theoretical and applied research. Both approaches benefit from rigorous field studies that improve our understanding of the large and diverse effects of urbanization on birds. We identify three broad approaches that are necessary to improve this understanding: (1) long-term research that utilizes an experimental and observational approach, (2) research that explores urbanization among multiple spatial patterns, and (3) research that examines urbanization effects at multiple biological levels of organization across gradients of variable urbanization intensity. The urban gradient itself needs better quantification. Many effects of urbanization are obvious (loss and degradation of habitat, introduction of exotics, changes in predator communities). However, less obvious and often indirect effects of urbanization (climate change, human disturbance, ecosystem disruption, effects on physiological systems, food supplementation) exist that should be explored further. If one application of this research is to mitigate the deleterious impact of urbanization on birds, then it is important to consider cogent social and economic aspects in our research designs. Involvement of all relevant stakeholders and interdisciplinary approaches to the study of urbanization's effects can increase the chances that our science will be incorporated into effective policy.
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