Date of Award
Master of Science (MS)
Eric K. Bollinger
Black-capped (Poecile atricapillus) and Carolina Chickadees (P. carolinensis) have distributions that span the northern and eastern portions of the United States. The areas where these distributions meet are called contact zones and extend from Kansas to New Jersey. Contact zones often have a narrow range of hybridization and usually within these zones of hybridization we will see a mixture of genetic, morphological, and cultural traits. One focus of this project was to compare morphology and genetics of chickadees within and near the largest Illinois contact zone, which has not been done previously. This contact zone was delineated by Enstrom and Bollinger (2009) based only on song structure and not on genetics or morphology. I placed 150 nest boxes within and on the edges of this contact zone in central Illinois. To examine the extent of hybridization occurring in this area, nestlings and adults were weighed and measured. Blood and tissue samples were also taken for genetic analyses. Results showed that although clutch size was similar across all sites, the hatchability of eggs differed significantly. This would suggest a reproductive depression in areas of hybridization, which is to be expected. I also found that wing chord and tail measurements for most individuals were Carolina-like with only individuals from the northernmost site having black-capped-like morphology.
I also examined a chickadee vocalization known as the "gargle" call. This short and complex call is often used in agonistic situations and sometimes immediately preceding copulation. Gargles were recorded year-round from areas surrounding the nest boxes. Recordings were conducted in one minute intervals, for up to five minutes at a time. Across sites, I compared the core components of the gargle, such as the start frequency, maximum frequency, minimum frequency, and end frequency.
These results showed a high amount of variation within the call across all sites. Another component examined was the syllabic composition. Although there were three universal syllables found at all sites, there was considerable variability in the overall abundance and patterns of all other syllables. Overall, my results indicate that the individuals within the Illinois contact zone are genetically more similar to Carolina Chickadees than Black-capped Chickadees. More extensive genetic and behavioral studies are necessary in order to determine the extent of hybridization occurring throughout this area.
Regan, Shannon Marie, "Morphology and Variation in the Gargle Call in a Chickadee Hybrid Zone in Central Illinois" (2017). Masters Theses. 2861.
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