Modification of natural habitats used by native organisms is occurring more rapidly due to the increasing human population. American Robins (Turdus migratorius) are common in urban and non-urban areas and can serve as useful indicators of human activities' effects on wildlife. To create an urban environment, the removal of trees from non-urban habitats is necessary but causes radical alteration of the presence of native avifauna. This study, therefore, examined the influence of tree cover within urban and non-urban sites and how trees' characteristics affected the survival rate of American Robin chicks. Data collection occurred during the 2019 breeding season (May-August) at twelve nesting sites that were categorized urban or non-urban based on distance from the city center of Greeley, Colorado. Nest monitoring occurred from clutch initiation to fledging. A circular plot (0.2 ha), with the nest at the center, was surveyed for tree density, tree height, the diameter of trees, and cover provided by the trees. I found that a single principal component could explain >55% of the variability in plot characteristics surveyed, but this variable did not significantly predict nest survival (Linear Regression: p=0.2721). I found no difference in clutch survival between urban and non-urban sites (Wilcoxon 2-sample Z-test: p=0.7483). These results suggest that the American Robin, regardless of urban or non-urban habitat characteristics, are nesting in locations similar in number, diameter, and height of trees as well as in areas with the same amount of cover provided by trees. Bird populations in North America have declined by 2.9 billion individuals since 1970. Considering many of these populations have been classified as stable until this time, continued investigation of how vegetation characteristics contribute to clutch survival rate, and by extension, population levels is an essential step to avian conservation in urban landscapes of the world.
Lawson, B. (2020). The Birds and the Trees. Retrieved from https://digscholarship.unco.edu/mcnair/2