Urban Birds


Summary of Geographic Patterns

Species Richness

The largest numbers of urban birds are generally found in the eastern half of North America, while the fewest occur in the western half.

Population Trends

Declining trends prevail in most of North America west of the Rocky Mountains, along the eastern edge of the Great Plains from Minnesota and Iowa south to Louisiana, and across eastern North America from the Ohio River south to the Gulf of Mexico. Regions with predominantly increasing trends are limited to the central Great Plains from Texas north into Canada, the central Rocky Mountains, and from the Great Lakes across New England.


Discussion

Urban birds comprise the smallest of the habitat-related bird groups, and are species that are most closely associated with urban and intensively-farmed habitats. Approximately 31% of the species exhibit positive trend estimates, the lowest percentage of any group except for grassland birds. Their generally declining populations may largely reflect changing land use practices on the continent's farmlands, especially "clean farming" practices that may have reduced the amounts of waste grains and other foods available to support these species.

It has been suggested by a reviewer that observer bias might influence our perception of population change in these species. Most of these species are not of particular interest to birders, and over time observers may record fewer individuals because they "tune them out" in favor of more interesting species. In any count-based survey, we must consider the possibility that changes in counts do not reflect changes in the actual populations. Unfortunately, this aspect of observer-associated bias cannot be easily evaluated from analysis of the data.