Cardueline Finches Vary in Constitutive Innate Immunity Against a Harmful Strain of Avian <i>Salmonella</i>

Cardueline finches readily occupy bird feeders in high numbers, but they are at risk of being infected by pathogens, such as Salmonella spp. Historically, pine siskins (Spinus pinus) often develop salmonellosis and succumb to the pathogen in high numbers during outbreaks in comparison to other Cardueline finches. Even though Salmonella spp. outbreaks in pine siskins are well-documented, there are no studies explaining why they die of salmonellosis at a higher rate than other birds. We hypothesized that pine siskins have a decreased bactericidal ability when compared to other Cardueline finches. We tested this with a bacteria killing assay (BKA) against Salmonella Typhimurium cultured from a local pine siskin that succumbed to the pathogen. We compared their BKA results against S. Typhimurium to three other local finches: lesser goldfinches (Spinus psaltria), American goldfinches (Spinus tristis), and house finches (Haemorhous mexicanus). We found that the Spinus spp. cannot kill S. Typhimurium as effectively as house finches. There were no significant differences between the two goldfinches, but the BKA results for pine siskins were significantly higher than those of the goldfinches. House finches had killing activity nearly twice that of pine siskins and more than twice that of the goldfinches. Our results highlight that the constitutive innate immune response against Salmonella spp. in some finches may be best explained at the genus level. We speculate that pine siskins' poor constitutive innate immunity and their irruptive behavior may make them more susceptible to Salmonella spp. over their less irruptive congeners.