Climate models predict that rising temperatures will shift disease vectors northward, potentially introducing novel pathogens like avian malaria to native species. Avian malaria's impact on birds during the breeding season is well studied, but little is known about its effects in overwintering habitats. The white-crowned sparrow (WCSP, Zonotrichia leucophrys), which winters in California's Central Valley, is vulnerable to avian malaria. Blood samples from WCSPs collected since 2021 revealed that ~40% were positive for malaria DNA, suggesting active or latent infections. To understand the relationship between malaria infectivity and host genetics, we focus on the major histocompatibility complex (MHC) class I gene, which plays a crucial role in immune responses. DNA from ~100 WCSP samples was extracted, and MHC class I exon 3, a region with high molecular variation, was amplified using PCR. The samples were sequenced on the Illumina MiSeq platform, and bioinformatic analyses will identify MHC alleles and their correlation with malaria prevalence. We will also analyze molecular evolution rates using the Datamonkey molecular evolution server and PAML (phylogenetic analysis by maximum likelihood). This study aims to reveal how MHC variation influences malaria infectivity and shapes evolutionary dynamics in songbirds during overwintering.