Variation in plasma protein levels in House Finches (Haemorhous mexicanus): effects of season, disease state, and urbanization

Bioindicators of wildlife health are useful tools for studying the viability of various organisms and populations, and can include a range of phenotypic variables, such as behavior, body size, and physiological parameters, such as circulating hormones and nutrients. Few studies have investigated the utility of total plasma protein as a predictor of environmental or nutritional variation among birds, as well as variation across different habitats and life-history stages. Here, we examined relationships between plasma protein and season, urbanization, sex, body condition, molt status, and disease state in House Finches (Haemorhous mexicanus). We sampled blood from House Finches across three seasons (winter, summer, and fall 2021) and measured plasma protein levels using a Bradford assay. We also collected data including condition, sex, and poxvirus infection state at capture, as well as fecal samples to assess gut parasitism (coccidiosis). During the fall season, we also estimated molt status, as number of actively growing feathers. We found a significant relationship between circulating protein levels and capture site, as well as novel links to molt state and pox presence, with urban birds, those infected with pox, and those in more intense molt having higher protein levels. Our results support the hypotheses that plasma protein concentration can be indicative of a bird’s body molt and degree of habitat urbanization, although future work is needed to determine why protein levels were higher in virus-infected birds.