Population Genetics of Western Bluebirds

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Western bluebirds (Sialia mexicana) are an obligate cavity-nesting bird species that experienced mid-20th century declines due to habitat loss and increased competition for available breeding cavities. Widespread nestbox placement has largely facilitated the recovery of this species, however eBird data suggests regional heterogeneity; some populations have increased in abundance, and some populations are decreasing. The Putah Creek Nestbox highway was constructed in the year 2000 by Dr. Melanie Truan (UC Davis Museum of Wildlife and Fish Biology) and coincided with major habitat restoration of the Putah Creek. Before the installation of these nestboxes, Western bluebirds were rare in this area, however there has been a significant increase in sightings and breeding success, with this species being amongst the top breeding species in the area. 

Population declines and expansions provide powerful natural experiments for testing fundamental principles of population genetics. Theory predicts that small or isolated populations experience reductions in genetic diversity due to genetic drift, elevated inbreeding, increased runs of homozygosity (ROH), and declines in effective population size (Ne). Conversely, rapid population expansion may either restore diversity through gene flow or amplify founder effects, depending on connectivity and demographic history. I will use whole-genome sequencing to (1) generate a high-quality reference genome for the species and (2) quantify genome-wide diversity, inbreeding, effective population size, and population structure across Western bluebird populations throughout their breeding range. Comparative analyses among populations exhibiting differing demographic trends will test whether genomic diversity and inbreeding track contemporary population decline or stability. Building upon this range-wide framework, I will then evaluate the Putah Creek Nestbox Highway population in finer detail to determine its geographic origin and assess whether it represents a founder-derived lineage resulting from recent expansion or a genetically connected part of a broader metapopulation.