Meeting Abstract
Human-induced changes to climate and habitat (e.g., urbanization) can facilitate traditionally migratory animals becoming year-round residents. As migration can be energetically expensive, shifts to sedentary behavior may minimize energy demands from long-distance movements and their immunosuppressive effects. Residency in urban habitats could further minimize energetic demands owing to abundant food resources and allow sedentary animals to invest more in immunity. To examine how recent shifts to residency affects physiology in ways that may shape disease dynamics, we analyzed leukocyte profiles of two dark-eyed junco (Junco hyemalis) populations in southern California: the Laguna Mountain population, which breeds in high-elevation forests and migrates altitudinally, and the urban San Diego population, which was likely established by overwintering migrants in the 1980s and has become non-migratory. Over a two-year study of each population’s breeding season in 2006 and 2007, we found no difference in the ratios of heterophils to lymphocytes between populations, suggesting similar baseline glucocorticoid levels. However, urban residents had higher total leukocytes than migrants, together suggesting minimal differences in energetic demands between populations. However, urban residency may confer immunological benefits through abundant anthropogenic resources. To explore the epidemiological consequences of such benefits, we outline a susceptible–infected–latent–infected modeling framework that couples migrant–resident interactions and their respective annual cycles. By varying the strength by which urban habitats modify host resistance and competence of residents, alongside migration-induced relapse, we show how these individual-level changes can scale up to shape population-level infection dynamics.
