Master of Science
The potential of migratory animals to spread infectious diseases depends on how infection affects movement. If infection delays or slows the speed of travel, transmission to uninfected individuals may be reduced. Whether and how malaria (Plasmodium spp.) affects bird migration has received little experimental research. I captured 40 actively-migrating Yellow-rumped Warblers (Setophaga coronata) at a migration stopover site and held them in captivity. I inoculated 25 with P. cathemerium while 15 received sham inoculations. After 12 days the birds were released. Six P. cathemerium-inoculated birds (24%) developed P. cathemerium infections after inoculation. I radio-tagged all birds, and used radio signal strength variability as an index of activity before and after release. I radiotracked birds at the release site to measure stopover duration. Experimental groups (Infected, Exposed but uninfected, Sham) did not differ in activity levels before or after release, nor in stopover duration. This research suggests that birds do not alter the migratory stopover behavior in response to avian malaria.
Summary for Lay Audience
Migration is increasingly recognized as a potential factor that may influence the spread of infectious diseases. Most migratory birds do not migrate in one long flight, but instead take breaks of days to weeks to refuel at migratory stopovers, and diseases may be particularly likely to spread among individuals (or indirectly through insect vectors) at these stopover sites. If infected birds are delayed in their migration, e.g. taking longer to refuel at stopover, this may reduce their encounters with uninfected birds, thus limiting opportunities for disease to spread. Approximately two-thirds of bird species are affected by avian malaria, a common disease that causes symptoms such as reduced movement, reduced eating, and damage to blood cells. Little is known about how this disease affects bird migration, and experimental information is particularly lacking. I captured and kept captive 40 Yellow-rumped Warblers during fall migration, fitted them with radio-tags to track their movement and activity, and experimentally inoculated 25 of them with avian malaria. Six birds developed malaria (the Infected group) and 19 did not (the Exposed but uninfected group). The remaining fifteen birds were not inoculated with malaria (the Sham group). Twelve days after inoculation I released the birds and continued radio-tracking them until most individuals had left the release site. There was no difference in activity between groups either in captivity or after release, nor in duration of stay at the release site. This suggests that being exposed to and/or infected with avian malaria does not change how birds behave at a stopover. If so, infection-induced delays are not likely to restrict the spread of avian malaria, at least in this combination of bird and parasite species.
Howe, Rebecca J., "Effects of Experimental Malaria Infection On Migration of Yellow-rumped Warblers (Setophaga coronata)" (2022). Electronic Thesis and Dissertation Repository. 8374.