Vertebrate anti-mosquito behavior may be an influential factor mitigating mosquito feeding success and, ultimately, the transmission of mosquito-borne pathogens such as West Nile virus (WNV). Anti-mosquito behavior may also influence the efficacy of bird-baited sentinel programs. The failure of sentinel chickens for WNV surveillance in New York state may be due to intense chicken anti-mosquito behavior against local mosquito vectors. We tested this hypothesis using two approaches. First, we examined the nocturnal anti-mosquito behavior of two avian species--the domestic chicken and the house sparrow--against varying densities of host-seeking females. Interspecific and intraspecific variation in frequency of anti-mosquito behavior among the avian hosts was compared. Mosquito blood-feeding success was also compared by host species, individual bird and mosquito density level and correlated with the degree of defensive behavior exhibited. The implications of these results to WNV surveillance using sentinel birds will be discussed.