Data from: Morphological measurements and mercury levels of Saltmarsh Sparrows sampled across their breeding range

Malaria parasites (genus Plasmodium) are important agents of infectious
disease in birds and multiple factors including warming temperatures and
environmental contamination may act to increase their geographic and host
ranges. Here, we examined the role of geographical variation and
environmental mercury exposure in malaria parasite infection dynamics in
an imperiled songbird species with high mercury exposition, the Saltmarsh
Sparrow (Ammospiza caudacutus). Using PCR methods, we screened 280
Saltmarsh Sparrows from across their breeding range for malaria parasite
infection. We detected malaria parasites in 17% of sampled birds and a
total of six Plasmodium lineages. Prevalence of infection and diversity of
parasite lineages varied across the breeding range of the Saltmarsh
Sparrow and increased at more northern latitudes. Although mercury is a
known immunosuppressant and has been documented to alter an individual’s
susceptibility to pathogens, we did not find a significant difference in
blood mercury levels between infected and not infected birds, perhaps due
to sampling methods and/or small sample sizes. As a specialist of coastal
wetlands, the Saltmarsh Sparrow is an excellent indicator species for
ecological health, and the patterns of malaria parasite infection with
host distribution and mercury suggest that birds at northern latitudes are
at greater risk of disease and should be priorities for conservation,
habitat, and pathogen monitoring.