Print PageA body of evidence is accumulating that host migratory behavior has important consequences for infectious disease transmission. Specifically, it has been posited that migration itself may be a mechanism for reducing infection prevalence through hosts periodically vacating sites where transmission occurs ("migratory escape"), or energetic costs of migration resulting in a lower survival probability of infected individuals ("migratory culling"). While empirical evidence suggests that these mechanisms may be operating, to date no theoretical framework has been developed to determine the ecological and environmental conditions under which migratory escape and culling may occur. Here I develop a general model for a host species undergoing an annual, two-way migration, and its directly-transmitted pathogen. Transmission is assumed to occur primarily on the breeding grounds, and infection may result in a cost to host fecundity and/or survival at various points in the migratory cycle. For a given set of environmental conditions, I compare the equilibrium host population sizes in the presence and absence of disease, for a range of host migratory strategies characterized by the time spent at the breeding site and the distance migrated.
Results/Conclusions
I find that an emerging infectious disease with high virulence may drive a migratory host population to dangerously low densities. Hosts that spend relatively little time on the breeding grounds and undertake long-distance migrations may be able to avoid infections that would otherwise attain endemic equilibrium in resident host populations. If infected individuals experience a relatively high mortality cost during migration, the optimal migration strategy for diseased populations is to spend less time at the breeding site and to migrate further than disease-free populations, providing support for both the migratory culling and migratory escape hypotheses.
