The conversion of forests to cities has hurt the populations of many kinds of birds. There are, however, a few species that appear to thrive in urban areas but little study has been devoted to the factors that affect their populations.
Researchers from the Smithsonian Migratory Bird Center monitored the nests of 5 common backyard birds:
The study area included rural, residential, and urban areas in the Washington, D.C. region. The data was collected by citizen scientists as part of the Neighborhood Nestwatch program and by scientists.
Surprisingly, the nests fared better in urban areas, sites with fewer trees and more roads, buildings, and sidewalks. This was most true in fairly large areas, about 1000 meters around the nest.
So why would urban nests do better than nests in the country or the suburbs? It likely has to do with the predator community.
To examine the predator community, fake nests were put out and monitored. They each contained 2 quail eggs and a clay-like egg that would show tooth or beak marks, depending on what tried to eat it.
The marks on the eggs showed that in urban areas, the nest predators are mostly other birds, such as jays and crows. In more rural areas, additional predators included squirrels, chipmunks, and mice. The lack of mammalian predators in urban areas seems to make nests safer.
But just because city nests are safer does not mean that urban birds have it easy. In the related articles below you can find out about the reduced amount of food in urban areas and the increased amount of contaminants.
One additional point to acknowledge is the contribution of citizen scientists monitoring nests in their own yards. Their data was compared to that of the scientists and it was found to be just as valid.
This article summarizes the information in this publication:
Ryder, Thomas, Reitsma, Robert, Evans, Brian and Marra, Peter P. 2010. Quantifying avian nest survival along an urbanization gradient using citizen- and scientist-generated data. Ecological Applications, 20(2): 419-426.
Despite the increasing pace of urbanization little is known about the factors that limit bird populations (i.e., population-level processes) within the urban/suburban land-use matrix. Here, we report rates of nest survival within the matrix of an urban land-use gradient in the greater Washington, D.C., USA, area for five common songbirds using data collected by scientists and citizens as part of a project called Neighborhood Nestwatch. Using program MARK, we modeled the effects of species, urbanization at multiple spatial scales (canopy cover and impervious surface), and observer (citizen vs. scientist) on nest survival of four open-cup and one cavity-nesting species. In addition, artificial nests were used to determine the relative impacts of specific predators along the land-use gradient. Our results suggest that predation on nests within the land-use matrix declines with urbanization but that there are species-specific differences. Moreover, variation in nest survival among species was best explained by urbanization metrics measured at larger "neighborhood" spatial scales (e.g., 1000 m). Trends were supported by data from artificial nests and suggest that variable predator communities (avian vs. mammalian) are one possible mechanism to explain differential nest survival. In addition, we assessed the quality of citizen science data and show that citizens had no negative effect on nest survival and provided estimates of nest survival comparable to Smithsonian biologists. Although birds nesting within the urban matrix experienced higher nest survival, individuals also faced a multitude of other challenges such as contaminants and invasive species, all of which could reduce adult survival.
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