As urban environments become increasingly common habitat for many animal populations, it is critical that we understand the effects of urbanization on the prevalence, transmission, and impacts of parasites and pathogens. Birds colonizing urban habitats could be faced with higher parasite pressure due to decreased avian diversity, increased population density, and loss of migration. Alternatively, urbanization may destroy vector habitat, reducing exposure to vector-borne disease. We tested these hypotheses by measuring parasitism of a native songbird, the dark-eyed junco (Junco hyemalis) at 11 sites in 3 habitat types in California: 5 urban coastal, 3 non-urban coastal, and 3 non-urban inland. We studied parasites that varied in transmission mechanism, and predicted that birds at urban sites would have higher prevalence of directly- and environmentally-transmitted parasites, and lower prevalence of vector-borne parasites. We tested effects of climate by comparing coastal and inland non-urban sites. Adult male birds (n=310) were captured during the breeding season. We detected haemosporidian parasites by nested PCR of DNA from venous blood; Trypanosoma and microfilaria by microscopy of fresh plasma; lice by dust-ruffling plumage with insecticide; ticks and feather mites by visual inspection of plumage; and coccidia oocysts by passive collection of fecal sample, flotation, and microscopy.
Results/Conclusions
Preliminary results show that probability of infection by most of the parasites measured is lower at urban sites, and may not depend on transmission mechanism. Probability of vector-borne haemosporidian infection was lower at urban sites, but did not differ among coastal vs inland non-urban sites. Haemosporidian lineage diversity data (including Haemoproteus, Plasmodium, and Leucocytozoon) are pending. The other vector-borne parasites measured did not show the same pattern: Trypanosoma infection was not predicted by habitat type, and microfilaria infection was more likely at inland sites, but did not depend on urbanization. Among directly- and environmentally-transmitted parasites, patterns were similarly diverse: likelihood of tick parasitism was higher at coastal, non-urban sites than urban or inland sites; lice parasitism was less likely at urban sites, but did differ among coastal and inland non-urban sites; feather mite parasitism was more likely at coastal sites, but did not depend on urbanization. Coccidia results are pending. We conclude that urban birds may experience different parasite pressures than non-urban conspecifics; for most parasites studied, probability of infection was lower at urban sites. These results inform our understanding of the ecology of urban birds as well as emerging challenges in both wildlife conservation and human and animal health.