American Goldfinch by Murray Head/Audubon Photography Awards
In Spring 2022, the Journal of Animal Ecology published an extensive study about avian nesting behavior and climate change conducted by a group of Chicago-based ornithologists. Researchers from University of Chicago, Lincoln Park Zoo, and the Field Museum utilized field observations and the museum’s historical records to track nesting dates for 72 species of birds spanning 143 years. This article not only serves as an interesting contribution to the scientific community, but also as a testament to the prominence of Chicago’s institutions and its urban ornithologists. In hopes of getting this information to as many birders as possible, past the inaccessibility of statistical jargon and academic pay-walls, we offer a short summary:
Climate change has implications on plant, animal and human communities all over the globe. Increasing temperatures in the Midwest would lead to shorter winters, drier summers, and more intense and unpredictable weather events. All of which would greatly impact bird populations if their nesting time and demand for food no longer line up with food availability. This research team focuses their attention on how increases in CO2 concentration (and thus temperature) over time may push birds to nest earlier.
Working with contemporary observational data and nest records from the Field Museum, they examine bird behavior and weather trends from 1872 to 2015. This 143 year period is nearly 50 years greater than any of the similar studies cited in the publication.
Some complexities of the study were somewhat lost on me, as I am not a statistician. While I wish I could speak on their specific equations and trend analyses, it may not be as fun for you to read. Overall, the study found that 24 of the 72 species (33.3%) advanced their initial nesting date, and only one species actually delayed its initial lay date. Interestingly, the only bird featured in this study that nested significantly later in the season was the American Robin. The authors speculate that American Robins may have certain traits that allow them to cope with changing climates or landscapes in the Midwest more effectively than their migrant counterparts.
As for the other species, they hypothesized that birds may shift to an earlier nesting date to maintain their thermal niche . Temperature is one of the main factors that determine where an organism can survive, so the term “thermal niche” describes the specific temperature range these birds require in order to thrive. Milder winters and hotter summer temperatures in Illinois may force those birds to nest earlier in the spring to get these ideal conditions. If temperatures dramatically increase before birds can adapt their nesting or migration behaviors, it would seriously impact their rate of survival.
Researchers assessed changes in initial nesting dates of 72 bird species broken into three categories: resident, short-distance migrant, and long-distance migrant:
RESIDENT SPECIES: 26 year-round resident species, 10 advanced their lay dates (mourning dove, American kestrel, killdeer, brown-headed cowbird, song sparrow, field sparrow, American goldfinch) and the American robin delayed its lay date.
SHORT DISTANCE MIGRANT: 14 short-distance migrant species, six species advanced their lay dates (Northern harrier, sedge wren, chipping sparrow, swamp sparrow, cedar waxwing)
LONG DISTANCE MIGRANT: 32 long-distance migrant species, eight advanced their lay dates (yellow-billed cuckoo, Cooper’s hawk, yellow-headed blackbird, yellow warbler, eastern wood-pewee)
This article proves how much there is to learn about climate change and its impact on specific animal relationships. Additionally, it is an example of how important museum archives can be for contemporary research. All of the new nesting data the team collected through this process could be archived alongside the museum’s existing database for later studies as well. Lastly, more as a personal note, it’s incredible to see such an in-depth study coming from urban ornithologists. It serves as a solid reminder for other readers that urban areas, especially the Chicago region, can be a hotspot for biodiversity, and deserve the same amount of attention for conservation efforts.
