Many avian hosts employ defensive behaviors to repel or kill host-seeking mosquitoes. We can make two opposing predictions from this behavior: it has the potential to either decrease avian arbovirus transmission (by reducing the number of bites per bird) or increase transmission (by increasing the number of multiple blood meals from different hosts). The efficacy of anti-mosquito defensive behavior may also be impacted by host illness, where sick hosts may be less defensive than others, thereby increasing the basic reproductive rate of the pathogen by ensuring mosquito transmission. Both of these processes are important to the epidemiology of disease transmission, yet poorly understood. To assess the role of disease in anti-mosquito defensive behavior, we evaluated defensive behavior of infected and non-infected house finches (Carpodacus mexicanus Muller) against host-seeking Culex pipiens pipiens L. First, one bird from each pair was infected with Mycoplasma gallisepticum. M. gallisepticum is an emerging pathogen that causes illness in house finches. We then cleared the infections using antibiotics. These treatments were compared with defensive behavior and mosquito feeding success in controls (two uninfected birds). In all trials, we measured intensity of anti-mosquito behavioral response by counting individual behaviors. We also genotyped microsatellite DNA in each blood meal to directly identify from which individual bird(s) each mosquito fed. By comparing healthy and diseased birds in terms of impact of host illness on intensity of defensive behavior and mosquito feeding preference, we can shed light on the potential of overt avian infection to enhance WNV transmission by mosquitoes.