Urban Birds

 

Consequences of Urban Landscapes on Wintering Bird Communities

Oscar Angell, Erik Hallberg, Solveig Olson

Grinnell College BIO 368

With rapidly increasing rates of urbanization happening worldwide, scientists have sought to understand how human environmental sprawl affects other organisms. There are many different species whose numbers have been negatively impacted as a result of increased signs of human presence such as habitat loss and litter we find in our oceans. However, there is not much information available on how overwintering bird populations are affected as a result of human presence as most studies have been carried out during the breeding season. There is knowledge of synanthropic bird species—such as pigeons, house sparrows, and crows—that benefit from human interaction. This apparent variation in birds’ responses to urbanization presents a certain nuance to the question: “How are overwintering bird populations affected by urban landscapes?”. An article published in 2016 set out to answer this question, considering how urban habitat structure, as well as human effects such as pollution, noise, and artificial light, impact overwintering bird communities in southern Poland.

As Ciach et al. point out, “urban areas account for almost 3% of the Earth’s land surface, and this proportion is continually rising” (547). The increasing expansion of human environments is one of the most harmful threats to non-human organisms, and vast species extinction on a global scale continues as a result of urban sprawl and its destruction of crucial natural areas. It is therefore necessary that the scientific community examines the effects of urbanization on biodiversity. One group of organisms that is largely present in urban areas is birds, and the specifics of their interactions and community assemblages within urban landscapes has yet to be studied in depth. Ciach et al. aimed to fill this gap in knowledge by looking at the ways in which bird communities wintering in urban areas are impacted by the habitat traits of an urban environment, including habitat structure, food availability, and light and noise pollution. To investigate this critical question, they used a line transect method to measure the composition, density, and interseasonal similarity of bird assemblage within 56 sample plots chosen at random in Kraków in 2014-15. Notably, Kraków has an urbanization gradient, making it an especially useful study site.

Ciach et al.’s main findings are that bird populations and species diversity are negatively impacted by noise pollution and building density, and are positively impacted by food availability, urban greenery, and in some cases, light pollution. They hypothesized that noise pollution decreases bird population and diversity by drowning out bird calls. These bird calls are required for many bird behaviors, such as group foraging, coordination, and flocking. With some species unable to complete these behaviors, the bird diversity and population decrease. High building density was also found to decrease bird diversity. The authors hypothesized that this was due to a lack of shelter limiting the bird species that can thrive in urban areas. Conversely, greenery coverage (farmland or urban greenery) was found to increase the diversity of bird types, as well as the overall number of birds. The hypothesis offered for greenery’s positive impact is that it increased the amount of shelter, allowing for more species to survive. Unsurprisingly, food availability also played a role in determining population density. In urban areas, populations of synanthropic bird species were significantly higher in areas with large amounts of human byproducts that the birds would eat. The final and most surprising finding was that light pollution may have a positive impact on bird populations. Ciach et al. observed that as a result of light pollution, birds would start foraging behaviors earlier in the mornings, and keep foraging later into the night although this was not true in all situations, and some species were negatively impacted by light pollution. However, the researchers found the overall population did better with light pollution.

Table 8. Environmental predictors of winter bird community traits

 As an extension of the work of Ciach et al., our group studied bird communities on a college campus in rural Iowa, a space of approximately 120 acres surrounded by the town of Grinnell and vast expanses of agricultural crop farming. Similar to the methods of Ciach et al.’s study, we used a walking line transect, relying on the Merlin ID app to record and identify the presence of bird species with call recognition. For three weeks in October, we collected data from three different sections of the college campus, each with different combinations of habitat structure and greenery. Consistent with the findings of Ciach et al., bird species richness—reflected by the number of species counted in each location—increased with a higher proportion of urban greenery and building cover. While our study is far more limited in its temporal and spatial span, its findings are relevant and complementary to those of Ciach et al. and expand on their work by examining a much smaller and less densely populated urban landscape: a college campus. Considering future implications of our work, we believe that Merlin ID is a helpful tool for examining the effects of urbanization on bird communities on other college campuses.

Sources Cited

Ciach, M., Fröhlich, A. (2017). Habitat type, food resources, noise and light pollution explain the species composition, abundance and stability of a winter bird assemblage in an urban environment. Urban Ecosystems 20, 547–559. https://doi.org/10.1007/s11252-016-0613-6

Hanski, I. (2011). Habitat Loss, the Dynamics of Biodiversity, and a Perspective on Conservation. AMBIO 40, 248–255. https://doi.org/10.1007/s13280-011-0147-3

Lincoln, S., Andrews, B., Birchenough, S., Chowdhury, P., Engelhard, G., Harrod, O., Pinnegar, J., & Townhill, B. (2022). Marine litter and climate change: Inextricably connected threats to the world's oceans. Science of The Total Environment, 837, 155709. https://doi.org/10.1016/j.scitotenv.2022.155709