The First Highly Contiguous Genome Assembly for the Western bluebird (Sialia mexicana)

The western bluebird (Sialia mexicana) is a secondary cavity-nesting thrush that has experienced historical population declines, local extirpations, and more recent recoveries associated with nest box programs. Despite these regional successes, recent eBird estimates suggest continued range-wide declines and substantial geographic variation in population trajectories, making this species a useful system for future studies of demographic change, connectivity, and conservation genomics. However, genomic resources for western bluebirds remain limited, and no reference genome currently exists for any species in the genus Sialia. Here, we present the first high-quality de novo reference genome for S. mexicana. Using PacBio HiFi long-read sequencing from an adult female, we generated a highly contiguous, phased 1.3 Gb nuclear assembly with a contig N50 of 24.8 Mb and high BUSCO completeness of 98.3%. We annotated the nuclear genome using transcriptomic and protein evidence, identifying 16,656 protein-coding genes and 26,060 transcripts/protein isoforms. We also assembled a complete ∼16 kb mitochondrial genome from Illumina short-read data. This reference genome provides a foundational resource for future studies of population structure, genetic diversity, connectivity, demographic history, and adaptation in western bluebirds and related taxa.